A CONCEPTUAL FRAMEWORK FOR CLASSIFICATION OF CONSTRUCTION
RECEIVED: November 1995
REVISED: February 1995
PUBLISHED: March 1996
Anders Ekholm, Dr
Div. of CAAD, School of Architecture, Lund University,
SUMMARY: Classification is a means to facilitate communication
among actors in a field of practice. In the construction sector
classification plays a major role in specifications, structuring
of documents, calculation of costs, etc. The need for general
classification systems grows with the increased internationalisation
of the construction market and the rapid development towards a
computer integrated construction process based on computer aided
product data modelling. These processes require standardised ways
of describing construction artefacts, and classification is a
means to achieve this. Classification within the construction
sector is based on pragmatic tradition and national needs, but
internationally applicable classification tables must be founded
on a neutral conceptual framework. The ISO Technical Report 14177
"Classification of information in the construction industry"
aims at providing such a framework. This study analyses some basic
concepts within the ISO Technical Report, among others facility,
space, element, and work section, and suggests further developments.
Fundamental semantic and ontological theories are applied to define
some basic concepts within classification and to build a conceptual
framework for construction works. A general conclusion of the
study is that the proposed framework is useful as a foundation
for identifying classes for construction works. Among the more
specific conclusions are that: 1) a separate classification of
socio-technical user systems may be a useful background for classifying
infrastructure units, construction works, and spaces according
to the activities they support; 2) a classification of construction
work parts as "shape objects" is needed in the earliest
stages of the computer-aided design process; and 3) a definition
of space that includes its boundaries is proposed.
construction, facility, element, work section, space, CAD.
1.1 Background and scope of the project
The objective of the study at hand is to contribute
to the development of classification in the construction industry.
Classification is a means to facilitate communication among actors
in a field of practice. In the construction sector classification
plays a major role for structuring information in specifications,
structuring of documents and calculation of costs, for example.
A multitude of national classification systems exist and the increasingly
international market for building services has enhanced the need
for neutral international standards. Computer technology and user-interface
have developed during the 80's and 90's in a way that initiates
new needs for classification. Of special interest in the next
few years, are the relations to the standards for building product
models currently under development (CIB 1995).
Within ISO/TC59/SC13, a working committee of the
International Standardisation Organisation, there is a project
with the objective to develop principles for the building sector's
classification system. Results of this work are presented in the
ISO Technical Report 14177 "Classification of information
in the construction industry" (ISO 1994 a). Based on this
report, work on an internationally co-ordinated element classification
table has started within ICIS, the International Construction
The objective of this study is to analyse the basic
principles for classification of construction works, and to suggest
changes in these which accounts for the new needs and possibilities
of IT today. This, and continued work on terminology and definitions
both in Sweden and internationally, shall lead to useful results
for the construction industry.
The study presents a framework for conceptual modelling
and discusses some general classification concepts. With this
background, concepts in building classification are analysed,
with emphasis on concepts representing physical parts of construction
works. The demands for classification in the early stages of the
design process and for product modelling are discussed, and conclusions
and areas for further research are presented.
The term 'construction works' is used here as a
synonym to facility, see the definition in section 4.1.1.
2 A FRAMEWORK FOR CONCEPTUAL MODELLING
2.1 Frameworks and aspect models
To bridge the gap between researchers in construction
classification and product modelling it is necessary to develop
a framework for construction information that can be used by both
groups. In the following, an attempt is made to fill in some of
the gaps, and make a contribution to the development of a unifying
conceptual framework for the construction industry.
A commonly-accepted conceptual representation must
have a sound theoretical foundation as well as be relevant to
the practical needs for different applications. Depending on the
degree of specificity, conceptual representations have different
scope and complexity. Bunge (1974 a) identifies four different
kinds of conceptual representations, three of these are of increasing
complexity concerning objects of a specific species, and the fourth
concerns a larger collection of objects belonging to the same
genus. The examples for the construction context are provided
in parentheses by the author:
- Schema or model object, is a list of outstanding properties
of an object of a given species (e.g. construction product information).
- Sketch or diagram, is a graph of the components of an object
of a given species and their functions and relationships (e.g.
construction drawings, process flow charts).
- Theoretical model or specific theory, is a hypothetico-deductive
system of statements representing some of the salient features
of a thing of a given species (e.g. u-value theory and
theory of moment of force in beams).
- Framework or generic theory, is a theory representing the
features common to all things of a given genus (e.g. basic definitions
and generic structures of construction works information).
Bunge reminds the reader that conceptual representations
of real things have shortcomings; they are incomplete, and at
best "fairly faithful". To overcome these problems it
is necessary on the one hand to make several different representations
of the same thing, where each representation focuses on different
aspects; and, on the other hand, to improve the existing representations
by recurring research efforts.
Examples of theories of different complexity and
scope can be seen in the rapidly-developing product modelling
research today. Björk discusses five "layers" of
representations in product data modelling (Björk 1995):
- information modelling language,
- generic product description model,
- building kernel model,
- aspect model, and
- application model.
The first three of Björk's layers are generic
theories or frameworks, and may have different scope ranging from
generic objects, through products in general, to buildings. The
fourth layer deals with specific theories for buildings of specific
kinds while the fifth layer contains specific applications of
Proposals for frameworks belonging to the second
layer, generic product description model, concerning products
of different kinds have been developed in connection with STEP,
the Standard for Exchange of Product Model Data (ISO 1995 a).
The General AEC Systems Model, GARM (Gielingh 1988) is an example
of this. The IRMA, Information Reference Model for AEC, (Luiten
et al 1993) is another example of a generic product description
Frameworks belonging to the third layer, building
kernel model, have been developed by a number of researchers (Björk
1989 and 1992, Froese 1992, Luiten 1994, and Turner 1990). The
current work on the Building Construction Core Model is another
example (Tolman and Wix 1995).
The emphasis in product data model research in the
construction industry has shifted from providing global theoretical
models to describing aspect models covering the data needs of
very particular domains. The COMBINE project (Augenbroe 1994)
and CIMSTEEL project (Watson 1995) are examples of such models
belonging to the forth layer, aspect models, in the schema. Eastman,
in his review of the evolution of building modelling, regards
the dynamic application of different aspect models in a design
situation as the only viable approach to provide the building
product model needed (Eastman 1992).
The ontological framework presented in this study
belongs to the second layer in Björk's schema, the generic
product description model. This ontological framework has relevance
for the efforts in STEP to develop a generic theory or a "core
model" that is common to the entire industry. In its turn
it is based on a philosophical synthesis of a set of extremely
generic concepts like "object" and "relation".
If "language" is interpreted as such a set of concepts
it may be regarded as belonging to the first layer of the schema
called "the information modelling language".
The proposal for a conceptual framework for construction
works developed in this study belongs to the third layer in Björk's
schema. It has relevance for the efforts to develop a core model
within STEP for the building industry, the Building Construction
Core Model (Tolman and Wix 1995). The conceptual framework for
construction works can be used to identify classification classes,
for example classes relevant for product modelling in the early
2.2 Semantics of science: Terms and concepts
In everyday thinking, as well as in science, properties
of things in the real world are represented by concepts. In languages
and in formal descriptions these concepts can be designated by
symbols. In order to avoid confusion in communication, the relations
between symbols, concepts and the real world must be clarified.
Some of the misunderstandings between representatives from the
construction classification and the product modelling worlds can
be traced back both to the use of language and to the different
meanings of concepts. An example is the term 'element', which
in construction classification is considered to stand for one
characteristic function of a physical part of a building (ISO
1994), while the term in product modelling stands for a combination
of properties (ISO 1995 b).
In order to be able to discuss relations between
terms, concepts and facts, and more specifically to discuss differences
in reference and representation of concepts, some useful definitions
are necessary. Traditionally the relations between symbol (term),
concept and reality are presented with the so called Ogden's triangle,
but this schema does not distinguish between reference and representation
(Ogden and Richards 1994 ). Instead the definitions presented
here are based on Bunge's contemporary semantics of science (Bunge 1974
a, Bunge 1974 b).
The terms used in a language are symbols and designate
concepts, e.g. the term 'house' is a symbol that designates the
concept "house". The designation relation is conventional,
that is it is based on rules. The reference of the concept "house"
is the class of all things with house-like properties. A concept
therefore represents certain properties of an object, for example
the concept "house" represents certain spatial, functional
and experiential properties of things belonging to the class of
houses. The sense of the concept "house" is given by
a context of related concepts emanating from personal associations,
cultural tradition or scientific theories.
There is also a direct relation called denotation
between a symbol and the reference class of the corresponding
concept. For example the term 'house' denotes the reference class
of the concept "house". Similarly there is a direct
relation called connotation between the symbol and the sense of
the designated concept. An example of the connotation of the term
'house' are concepts related to "house" in personal
associations, cultural traditions or scientific theories. Finally
there is a relation of proxy between a symbol and the property
represented by the corresponding concept. A sign with the term
'house' may proxy, or stand for, house properties. These relationships
are shown in Fig. 1.
FIG. 1: Basic semantic concepts
2.3 An ontological framework for conceptual modelling
In the construction design process the designers
develop conceptual models of factually possible things, for example
construction works. In order to achieve clarity in communication,
research and technical development it is necessary to have a common
conceptual framework where basic terms and concepts such as property,
thing, system, and level are defined and related. Such a framework
is of an ontological nature and represents the basic structure
of reality, the concrete world of things (Bunge 1977, Bunge 1979).
Below, the ontological framework applied in this investigation
is presented. The objective of the investigation is to define
the basic concepts used in classification of construction works.
2.3.1 Property and thing
To describe an object is to account for its properties.
In order to distinguish different kinds of properties a comprehensive
theory of properties is necessary. In a general philosophical
sense objects are either abstract or concrete entities toward
which thought, feeling or action is directed. Concrete objects
are things with substantial or real properties,
while abstract objects are mental constructs with formal
properties (Bunge 1977). Substantial properties can be divided
into factual and phenomenal, see Fig. 2. Factual properties
exist independently of an interpreting mind, while phenomenal
properties depend on an interpretation of a sentient organism.
The phenomenal properties can be more or less objective
and subjective, that is they can be more respectively less
in accordance with the factual properties Examples of phenomenal
properties are percieved properties like colour and taste.
FIG. 2: Kinds of properties
Factual properties are either intrinsic or mutual. Mutual
properties are relational, they depend on relations to other things
like the environment or a reference frame. The relations between
a thing and its environment are bonding. Things with bonding
relations affect each other's state, for example integrating and
repelling relations are bonding. The relations between a thing
and a reference frame are non-bonding. Non-bonding relations
do not effect the states of the related things, examples of non-bonding
relations are spatial relations like position or shape. Phenomenal
properties are mutual non-bonding relations between a thing and
an interpreting mind.
Generally the distinction between intrinsic and
mutual properties depends on the demarcation of the system. A
mutual property may be construed as an intrinsic property of a
larger system. Man-made things, artefacts, are designed with a
purpose to have certain functions. A function is a mutual
property of a thing and its environment, for example of an artefact
and its users. A function is a bonding relation. Performance
may be defined as a measure of relative quality. In that sense
it is a mutual property based on a non-bonding relation to some
A simple or atomic thing has no parts. An aggregate
is a collection of things with only non-bonding relations. A complex
thing with bonding relations among its parts is a system.
A comprehensive description of a system's properties includes
its composition, environment, structure, laws and history. The
composition is the set of the parts of the system, the
environment is the set of things that interact with the
system and the structure is the set of internal and external
relations as shown in Fig. 3. A system's laws are relations
among its properties, and its history is comprised of the
former states of the system (Bunge 1979).
FIG. 3: Basic properties of a system (arrows
indicate one-way or two-way interaction)
The properties of a system are resultant and emergent.
A resultant property already exists among the system's
parts, such as weight, while an emergent property, such
as the stability of a structure, is new, and characterises the
system as a whole.
A compositional part of a system and the system
as a whole have a part-whole relation. Basic to the part-whole
relation is that the existence of a part precedes the existence
of the whole. The relation is defined for things only (Bunge 1977).
If the parts of a system are systems themselves they are called
subsystems. And if the total environment of a system is
a system it is called a supersystem.
A level is a set of things where things in
lower levels are parts of wholes in higher levels. The levels
subsystem, system, and supersystem together make up a level order.
A level order is a set of levels, where lower levels precede
higher levels. Seen from the direction bottom-up, when a system
is assembled, parts in lower levels are aggregated into wholes
in higher levels. In each new level properties emerge so that
the whole in some fundamental way differs from its parts.
2.3.3 Artefacts and socio-technical systems
Artefacts are man-made
or man-controlled systems; they are tools that make certain activities
possible. When man uses an artefact to perform an activity, a
new kind of system emerges, a socio-technical system (Emery
and Trist 1960). The activity is a property of the complex
socio-technical system of man and artefact, e.g. construction
works enable activities like driving a car smoothly at high speed
on a road, or farming in arid areas using the distribution of
water in pipes.
In a socio-technical system the purposeful relations
are functions. The intrinsic functions are tool-relations and
the individuals roles (Ekholm 1987). Tool-relations exist
between a person and the things a person uses as tools during
an activity. A role is a human activity and a subset of
an individual's behaviour performed for the system's purpose.
Among the extrinsic functions are the extrinsic roles and transformation
relations to the environment, see Fig. 8.
2.3.4 Functional and compositional views on
To adopt a view on a system is to observe a specific
set of properties. A functional view on a system focuses on some
of its bonding relations to the environment while a compositional
view on a system is directed towards its composition and internal
relations. In both cases spatial relations may be included, but
they may also be regarded as a separate view on the system. The
complete description of a concrete thing, e.g. a building, must
among others include both the functional and the compositional
aspects, see Fig. 4.
A "black box" model of a system with input
and output defined is an example of a functional view. A closer
study may reveal that certain functions are related to specific
areas of the system, the functions of these areas contribute to
the global functions of the system. The study of the human brain
is an example of this kind of functional analysis. Similarly a
study of a building will reveal that certain areas are loadbearing
and others are climate protecting. However the functional view
gives no clear indication what are the composition parts of the
system, since the same product can have many different properties
and can be part of many different functional systems. The functional
approach to identifying parts has been used in the GARM (Gieling
1988) and is also frequently used in everyday analysis.
The other approach is a compositional "bottom
up" view of the system, which identifies the composition
units of the system and studies how their properties contribute
to the functions of the system as a whole. According to the definition
of the part-whole relation the composition units are compositional
parts of the system, they are things that precede the whole, that
is they exist before the whole (Bunge 1979).
To conclude, a functional view does not reveal the
compositional units of the system; this is only achieved through
a compositional view. On the other hand, the naming of things
often uses a functional characteristic as basis, so compositional
units can also have functional names.
FIG. 4: Functional and compositional views on
3.1 Classification and knowledge
In order to classify a collection of objects it
is at first necessary to define the purpose of the classification.
Then the properties of interest to the classification may be distinguished,
and finally the objects can be sorted into classes with
regard to the chosen properties. This requires both factual knowledge
of the objects of interest and that the purpose of the classification
is carefully considered. In classification it is also necessary
to make methodological abstractions; that is, disregard properties
that are not of interest (Bunge 1983).
The distinction between classes can be based on
Boolean or Cartesian partitions. The former is qualitative, of
the form "A" and "not-A", while the latter
is quantitative of the form "more A" and "less
A". Only the former distinguishes definite classes. A detailed
description of the application of Boolean principles is given
in Bindslev's presentation of the CBC-system (Co-ordinated Building
Classification) (Bindslev 1969).
To classify is not to build a theory, "classifications
summarize and order available knowledge" (Bunge 1983). Bunge
draws attention to the fact that classifications come in several
depths and that "we should prefer the deepest of all for
being the more realistic. If we want deep classifications we need
theories, the deeper the better: for example, biological systematics
(based on the theory of evolution), the periodic table of the
elements (based on the atomic theory), the classification of hadrons
based on the quark model, and the classifications of materials
based on their constitutive relations or specific laws" (ibid).
3.2 Classification rules
A classification may be scientifically founded but
it is a conceptual operation to create order in a set of objects.
To a certain extent it must disregard the fact that things do
not have sharp boundaries; properties come in degrees, not in
distinct packages. A classification based on the factual intrinsic
properties of a thing is called a natural classification
while a classification based on factual mutual properties or phenomenal
properties like appearance is called an artificial classification.
A natural classification can be based on properties like heat
conductivity or constituent material. A classification based on
use is artificial, although use, as a mutual property of a thing
and the user, is based on intrinsic properties. Artificial classifications
can be based on external appearance like beauty or meaning, expressed
e.g. in the (questionable) proposition "only beautiful buildings
have architectural qualities".
FIG. 5: Classification concepts
In a classification a collection of objects are
sorted into different classes where each class is a set composed
by its members, and determined by properties relevant to the classification.
Properties that determine the classes in a collection can be ordered
by increasing fineness from general to specific. Properties of
a higher rank are general and properties of lower ranks are specific
to the members in the collection. See Fig. 5.
The purpose of a classification is to distinguish
between the objects in a collection. In order for the classification
to be exhaustive, every object in the collection must be assigned
to a class, and in order to be definite each object may only belong
to one class. Without these criteria there are unclassified objects,
and objects that belong to more than one class of the same rank.
In both cases the classes are not properly defined.
In a classification some important rules must be
followed (Bunge 1983). The classification must be:
1) exhaustive, the union of all classes in the first
grouping must equal the original collection, see Fig. 5, and
2) definite, there must be no borderline cases.
All the classes of the same rank must be pairwise disjoint. Two
classes are either disjoint, or one of them is included in the
other. An object may not belong to more than one class of the
same rank, see Fig. 6.
FIG. 6: Relations among classes in a classification
3.3 Direct and combinatory grouping
An attribute is a conceptual representation of a
property of a concrete or abstract object. The attributes in a
classification table represent characteristic properties relevant
to the objectives of the classification.
The members of a class have characteristic properties
in common. There are two different principles of grouping objects
1) direct grouping and 2) combinatory grouping (Wåhlin 1976).
In a direct grouping the classes are identified through a combination
of properties that serves the purpose of the classification, the
object's use can be among these. A direct grouping of the parts
of a building is wall, floor, foundation, roof, window, etc. In
a combinatory grouping one or more sets of attributes can be freely
combined. The latter classification structure is termed "faceted"
(ISO 1994, Wåhlin 1978).
A facet is an exhaustive set of properties of similar
kind e.g. functions that makes it possible to categorise all members
in a collection. A study of building classification systems shows
that principally three main facets are used namely "function",
"construction activity" and "material". An
example of a facet is the "main function" used in the
Swedish BSAB system, with the attributes "loadbearing",
"enclosure" and "servicing" that in an exhaustive
way can be used to classify parts of a building (Häggström
A faceted classification makes it possible to freely
combine a set of properties that characterise an object and is
capable of accepting new objects to be classified. "A faceted
classification has a distinct advantage over an enumerative one
in the kinds of search strategies it empowers as well as in expert
system applications making use of the synthesis and decomposition
of class numbers" (Svenonius 1992).
If a thing has more than one of the properties of
the facet it is necessary either to make a decision which property
should be used as primary for the classification, or to specify
the facet further. In BSAB 96 "loadbearing" is primary
to "enclosure" and other properties since there is a
user need to be able to separate all loadbearing components for
example for tendering purposes.
The same collection of objects can be classified
in different classification systems, for different purposes. A
pre-fabricated wall may be classified as a construction product
e.g. B211 Non-structural wall (EPIC 1993) and as an element e.g.
43.CB Internal wall (Häggström 1994). The same physical
part in this example belongs to different classes, but in different
classifications. However each of the classifications follow the
basic principles of being exhaustive and definite.
4 CLASSIFICATION OF CONSTRUCTION WORKS
4.1 Basic concepts
The basic concepts in construction works classification
represent properties that are of interest in the design, construction
and management processes. The fundamental units of interest are
construction works, users and producers. In this section some
classification concepts are defined in relation to the earlier
presented systems model. The concepts discussed here and in the
ISO Technical Report (ISO 1994 a) are: facility, space, element,
designed element, work section, production activity, construction
product, construction aid and attribute. In the new Swedish BSAB
96 system the related concepts infrastructure unit and construction
type are of interest and also discussed here.
4.1.1 Facility or construction works
According to the ISO Technical Report a facility
is: "A physical structure or installation, including related
site works, serving one or more main purpose". A building
is defined as: "a type of facility comprising partially or
totally enclosed spaces and providing shelter" (ISO 1994
a). The sentence "including related site works" is excluded
in BSAB 96, where "site works" are regarded as
a separate kind of facility.
An analysis of the examples of classifications of
facilities in the ISO Technical Report show that they are based
on four different kinds of properties. The first three are functional,
a) function with users, b) function with an installation, and
c) function with an environmental agent, and the fourth, d), is
based on intrinsic properties. Intrinsic properties of the last
category are loadbearing, enclosing, servicing, and spatial properties
of the facility. These properties are used to support different
kinds of functions. Examples of classes based on these different
aspects are shown in Table 1.
TABLE 1: Examples of properties used
for classification of facilities
|Properties for classification
||Examples of classes|
|Function with users||Museum, Pedestrian tunnel
|Function with an installation||Railroad, Boilerhouse
|Function with an environmental agent||Seawall, Rainshed
|Intrinsic properties||Building, Bridge, Mast, Tunnel, Dam
Since functions are based on the intrinsic properties of the facility,
for example a school building has a spatial structure suitable
for class-rooms and an auditorium, it is of interest to classify
facilities according to how they are used or their intended use.
But a classification based on use is artificial since it only
indirectly concerns the buildings intrinsic properties. The ISO
Technical Report does not discuss this problem but recommends
that facilities are classified according to user activities.
In the work of ICIS, the International Construction Information
Society, WG 3, there is an agreement that a classification of
facilities based on intrinsic properties is also feasible and
useful. For this purpose a suggestion has been made to introduce
a new concept, the "construction type". A construction
type is defined as: "an independent physical structure with
common object functions and basic geometry which therefore have
a common set of elements" (ICIS 1994)
The term facility used in the ISO Technical Report has the disadvantage
of being somewhat vague. The term "construction work"
has been used by Giertz to denote the class of "buildings,
roads, bridges, silos, off shore rigs etc." (Giertz 1982
a), the term is also used in civil engineering (ISO 1994 a). "Construction
works" designates the same concept as "construction
type" and has advantages over the latter since "type"
denotes membership of a certain subclass of constructions. Construction
work reminds of the Germanic words "bauwerk" and "byggnadsverk"
where "verk" is used with the same meaning as "work".
The conclusion is that if another term than facility should be
suggested, then "construction work" should be considered.
A construction work is an artificial system, built for
a purpose, it has a static ground construction, and relations
to the environment like the surrounding nature and users, see
Fig. 7 (Ekholm 1987).
FIG. 7: A system model of a construction work with function,
composition and internal structure
A construction work, as a whole, is a system of interacting parts
which may be divided into three main functional groups, loadbearing,
enclosure (against for example climate and intruders), and servicing.
Construction work parts interact and constitute systems of different
kinds with new functions. There are construction work parts of
varying complexities. Atomic parts like "wood frame"
and "gypsum sheath" make up a simple system with the
property "internal wall". Examples of simple systems
are wall, floor structure, roof, washbasin, bathtub, socket and
water tap. A wall is a system of interacting parts with the composite
function "wall". More complex functions are often properties
of systems in higher levels where many parts interact like loadbearing
structure or climate system.
Construction works are parts of socio-technical systems; they
are used as tools that make different activities possible. The
properties of the construction work are basic to many of the activities
performed by the users. It should be noted that there is no one-to-one
relation between a user organisation and a construction work,
which may accommodate several different organisations. Vice versa,
the same organisation may occupy several different construction
works. Therefore, it is not the use that delimits its extension,
but a combination of intrinsic properties like loadbearing, enclosure
and servicing that separate the construction work from its environment.
4.1.2 Infrastructure unit
Although it is not included in the ISO Technical Report, the concept
"infrastructure unit" is used in BSAB 96 which
makes it relevant to mention here. An infrastructure unit is not
a large construction work, it can be defined as an aggregation
of construction works that is used by a social organisation for
a purpose. An infrastructure unit is not a system since the definition
of a system includes bonding relations among its parts, see section
2.3.2. It is an aggregate with spatial relations that are necessary
for the functional properties in use. The infrastructure unit
and the social organisation together make up a socio-technical
system with activities as its main properties, see Fig. 8.
Just as facilities in the ISO Technical Report are classified
according to user activities, infrastructure units in the proposal
for BSAB 96 are classified according to the activities of the
socio-technical system, for example university, hospital, airport.
FIG. 8: An infrastructure unit can be seen as part of a socio-technical
In the ISO Technical Report spaces are defined as: "Three
dimensional spaces within and around buildings and other facilities,
bounded actually or theoretically" (ISO 1994 a). This is
not a proper definition since it presupposes the concept to be
The attributes in classification tables for spaces, just as in
classification of infrastructure units and facilities represent
functions in relation either to the users e.g. "lavatory"
and "dining-room", or a kind of installation e.g. "boiler-room",
or an external agent acting on the facility e.g. "rain"-shed.
This indicates that a space is a thing with certain geometrical
enclosing properties and that it can have a function.
A spatial relation is a non-bonding separation relation
among things, and space is a set of spatially related things
(Bunge 1977). The concept "space" refers to a set of
things and represents their spatial relations,
FIG. 9: Reference and representation of the concept "space"
see Fig. 9. The things need not constitute a system but form
an aggregate. A consequence of these definitions is that the only
way to describe and classify space is as things with spatial relations.
Spaces in a building are made up of building parts. These parts
have material properties and spatial relations that constitute
a suitable environment for user activities and things. Characteristic
for spaces in buildings are their enclosing properties. Although
non-exhaustive, a definition of "space" that could be
used as a basis for classification in the construction context
is: "A space in the construction context is an aggregate
of construction works, their parts or other things with materially
or experientially enclosing properties". An example of such
a space is a room in a building see Fig. 10. Outdoors, e.g.
a street-space may consist of a street, pavements and the surrounding
buildings. From the definition follows that a part of the building
may be a space, for example a pre-fabricated volume element, that
a building as a whole may be a space, and that a group of buildings
and other construction works may be a space.
Classification of spaces in the construction context is based
on their functions in use in a socio-technical system. Construction
works and spaces within and around these may also be classified
according to their geometrical properties, basically their shape.
One example of such a classification is the distinction between
houses based on their overall shape for example rectangular, L-formed,
U-formed or courtyard shape with their variants.
FIG. 10: Space as an aggregate of things with spatial relations
According to the ISO Technical Report an element is: "A physical
part or system of a facility with a characteristic function (e.g.
enclosing, furnishing or servicing building spaces), defined without
regard to the type of technical solution or the method or form
of construction" (ISO 1994 a).
The elements of a system are identified through a "top-down",
functional, view. Three major kinds of elements are distinguished
in the appendix B2 of the ISO Technical Report:
TABLE 2: Categories of use for an element classification according
- structure/enclosure elements;
- services engineering elements; and
- fixtures/equipment elements.
|Clients brief||Construction product data filing
|Written descriptions of design proposals
||General inform. on design requirements
||Project data filing
|Bills of quantities
|Historical data on designs
|Historical data on costs
||Life cycle costing
DecommissioningLars Magnus Giertz, developer of
the original SfB system, distinguishes three different actors
with separate interests, partly coinciding and partly conflicting,
relevant for identifying elements:
- the owner, with concerns for enclosure of space, and maintenance
- the architect: with concerns for elements grouped into functional
- the constructor: with concerns for elements grouped into sub-contracts
and sequence of building operations (Giertz 1982 b).
In the ISO Technical Report is listed a wide range
of uses of an element classification. The list of uses has been
structured and supplemented by ICIS WG 3 as shown in Table 2 (ICIS
The original SfB system was developed to facilitate
communication between the design and construction phases of the
building process. The table for elements was partly set up to
be used for identifying different kinds of drawings, the term
used was 'byggnadsdelar' which translated directly from Swedish
is 'parts of the building' (Bygg AMA 1950). The original table
for elements in SfB is shown in Table 3. This English version
is taken from Giertz (Giertz 1982 b).
TABLE 3: Building Elements in SfB 1950
|(0)||Accessories generally (compare (50) and (60)
||(45)||plints, mouldings, fillets, window sills, etc.
|(1)||Ground and foundation
||(48)||completions (sheet metal, etc.) to roof coverings |
|(12)||ditches, ducts, drains
||(5)||Services (mainly piped ducted)
|(13)||retaining walls, soil supports
|(14)||roads, paths, hard surfaces
|(15)||soft surfaces, lawns, planted areas
||(52)||services - drainage
|(16)||substructures generally, other than (17) and (18)
||(53)||services - water
||(54)||services - gas, compressed air
|(18)||pad foundations, footings, foundation beams |
|(55)||services - space cooling
||(57)||services - space heating
|(2)||Building elements (primary)
||(58)||services - ventilation|
|(21)||walls, external walls
|(22)||partitions, partition screens
||(6)||Services (mainly electrical)
||(63)||services - power, lighting
||(64)||services - telecommunication
|(26)||flat roofs, terraces, balconies
||(66)||services - lifts, escalators
||(68)||services - lightning conductors|
||(28)||building elements above roof|
|(3)||Building elements (secondary)
||(7)||Fixed furniture (commonly used)
||(71)||furnishing of entrances, etc.: racks, etc.
|(33)||additions to floors, floating floors, etc.
||(75)||furnishing of laundries and related rooms
|(34)||handrails and balustrades for stairs
||(72)||furnishing of rooms generally
|(35)||gates, barred openings, etc.
||(73)||furnishing of kitchens and related rooms
|(36)||terrace lights, balcony balustrades, parapets, etc.
||(74)||furnishing of toilets, baths, dressing rooms
|(37)||roof lights, roof trap doorways, etc.
||(76)||furnishing of rooms for cleaning and storing
|(38)||eaves, gutters, downpipes, roof walkways, etc.|
|(77)||furnishing of secondary spaces|
|(4)||Building elements (finishes)
||(8)||Fixed furniture (special for schools, hospitals, etc. (to be used as needed)
|(41)||wall finishes externally
|(42)||wall and ceiling finishes internally
||(9)||Site elements and site finishes other than those mentioned in group (1) (to be used as needed)
The original SfB system was organised so that the
physical parts of the building could be described from three separate
tables each representing a specific view. There were tables for
"elements", "production activities" and "materials".
The table for elements is an example of a direct grouping of the
parts based on a mixture of properties to identify an element.
In later applications "elements" have been seen as a
facet describing functional properties of the buildings parts.
The original idea was not purely functional but to make a combination
of different properties so as to be able to identify the parts
of the building uniquely without specifying their material contents.
One of the starting points for the development of the CI/SfB Construction
Indexing Manual was a criticism of the element concept for not
being a "pure" facet but a mixture of properties like
position, material, function, shape and uses (Giertz 1982 b).
Traditionally building classification only accounts
for so called characteristic functions, e.g. loadbearing, enclosure
and servicing. To be classified as an element, a part of the construction
must have at least one characteristic function, see Fig. 11. A
part without a characteristic function is not an element but may
be part of an element. Examples of such parts are "wood frame"
and "gypsum sheath". They are results of separate construction
activities but does not by themselves have a characteristic function,
see Fig. 14.
If a part has two or more characteristic functions
a main function must be distinguished in order that a part may
only be assigned to one class of the same rank. The primary property
is called the main characteristic function. In BSAB 96
there is a rule that if a part is both loadbearing and enclosure,
the order is that loadbearing is primary and enclosure is secondary.
The ranking is conventional and based on the Swedish contractors
requirements on the tables. However the generality of this order
may be questioned since from the user's point of view, enclosure
may be considered more basic than loadbearing.
FIG. 11: Construction work part as "composite
element", "element" and "designed element"
Just as with the concept "space", there
is a similar ambiguity with the meaning of the concept "element".
The term 'element' designates several different concepts, all
with reference to physical parts, compositional units, of construction
works. One concept represents a complex of properties of the part,
as in classifications using direct groupings e.g. the original
SfB system. This view is typical of ordinary language and is the
most common among construction classification professionals as
well as practitioners in the construction industry. Another concept
represents the characteristic function of a physical part, and
is used within the combinatory approach in faceted classification,
for example in the development of the new BSAB 96 system,
see Fig. 12.
The difference in meaning of "element"
reflects the two main approaches, direct and combinatory, in classification
and must be observed in communication between actors in the field.
The definition in the ISO Technical Report can be interpreted
in both ways and thus be accepted for both applications, however
the different interpretations may lead to completely different
conclusions. In both cases "element" refers to physical
parts of construction works, the difference lies in the scope
of the concepts. The concept used for direct grouping gives both
a more generic and complete representation of a part, while the
concept used to represent only one characteristic function gives
a more specific and limited description. In the very beginning
of the design process the combinatory concept of "element"
cannot be used since the functions of the parts are not determined
far enough at this stage.
FIG. 12: Reference and representation of different
A somewhat different idea of the element concept
is presented by Bindslev in his CBC system. Elements according
to Bindslev are general location properties (Bindslev 1969, Bindslev
1992). Giertz has explained Bindslev's concept of elements as
"dimensionally and functionally defined space" (Giertz 1982 a).
The CBC system describes the building or building
project using a "general code". The code consists of
a classification part and an identification part. The former is
a combination of codes from the three SfB classification tables
that enables a complete description of a certain class of physical
parts of the building, and the latter is an identification of
a particular member of the class. This is exemplified with the
code (22)Fg2.1234 that denotes a clay brick construction "located
in the building element 'partitions'" (Bindslev 1969). This
analogy implies that an element is a space that can be filled
with constructions. It reveals a conception of space as a separately
existing void entity. This contradicts both physical science and
common sense where an element is regarded as a physical thing.
Another interpretation is that Bindslev's element concept represents
spatial properties of physical parts so that Bindslev's elements
are spatially defined parts of the building, see Fig. 12.
To organise a table for elements raises also other
questions that cannot be subject for this investigation, e.g.:
How fine-grained should an element classification be? The use
of the tables is a determining factor for their structure. An
element table is to be used in the context of specification and
the degree of detail must allow different technical solutions.
How should the tables be structured? The order of the attributes
in the BSAB 96 element table is based on the sequence of the construction
activity, and an order of complexity of work (Häggström
1994). A third question is whether to integrate tables for different
kinds of construction works or settle with a common conceptual
basis but with different applications. In the BSAB 96 system roads,
railways etc. use the same tables as buildings, see Table 4.
4.1.5 Composite element
In the BSAB 96 system there is a strict order in
the classification which rules that if a physical part is both
loadbearing and enclosure it must belong to the class of loadbearing
parts. The reason for this is determined by the users of the tables,
for example contractors find it relevant. If the main characteristic
function is not determined or unknown, the part is classified
as a composite element (Häggström 1994). The
composite element is intended to be used in the early stages of
the design process when the main function has not yet been determined,
see Fig. 11.
In the the ISO Technical Report, appendix B 2: ELEMENTS,
is suggested that the primary element is a useful attribute in
classification for the early stages of the design process. The
ISO Technical Report distinguishes between primary elements and
functional parts or systems. Examples of primary elements are
"foundations", "lowest floor", "internal
walls" etc. Examples of functional parts are "main fabric",
"false ceilings" "floor finishes" etc. The
functional parts represent a further specification of the properties
of the primary elements. The question of classes for the earliest
stages in the design process is discussed further in section 5.
TABLE 4: BSAB 96 draft version 1994-04-14, table for elements
NOTATION / HEADING
|0||COMPOSITE ELEMENTS INCL. SERVICES ENGINEERING ELEMENTS
|01 Composite elements
|02 Composite services engineering elements
|03 Composite elements incl. services engineering elements - other
|1||SUPPORTING SOIL, SUBGRADE, PROTECTING LAYER IN GROUND; FOUNDATION AND RETAINING STRUCTURES
|10 Composite supporting soil, subgrade, protecting layer in ground; foundation and retaining structures
|11 Supporting soil (natural, excavated, reinforced)
|13 Layer in ground for protection of construction works
|14 Layer in ground for protection of nature
|15 Foundation structures
|16 Retaining structures
|2||LOAD CARRYING STRUCTURE
|20 Composite load-carrying structure
|21 Load-carrying structure in bridge, jetty, quay/embankment, and such like
|22 Load-carrying structure in tunnel, rock-chamber, and such like
|23 Load-carrying structure in mast, tower, lighthouse, and such like
|27 Load-carrying structure in building
|29 Other load-carrying structure
|3||PAVEMENTS AND CIVIL ENGINEERING WORKS COMPLETIONS
|30 Composite pavements and civil engineering works completions
|32 Civil engineering works completions
|4||SPACE-ENCLOSING ELEMENTS; BUILDING COMPLETIONS; SURFACE FINISHES, AND ROOM FITTINGS & FIXTURES
|40 Composite space-enclosing elements; building completions; surface finishes, and room fittings & fixtures
|41 Roofs (not carcass); climate separating parts and completions
|42 External walls (not carcass); climate separating parts and completions
|43 Interior space-enclosing elements
|44 Interior surface finishes
|45 Building completions
|46 Room fittings & fixtures
|49 Other space-enclosing elements; building completions; surface finishes, and room fittings & fixtures
|5||PIPE AND DUCTWORK SYSTEMS, DISTRIBUTION NETWORKS
|51 Water conduit -, sewage -, gas -, and district heating networks, etc.
|52 Water and gas systems, etc.
|53 Waste management systems
|55 Cooling and heat pump systems
|56 Heating systems
|57 Air treatment systems
|58 Fire protection systems
|6||ELECTRICAL AND TELECOMMUNICATIONS SYSTEMS
|60 Composite electrical and telecommunications systems
|61 Electrical and telecommunications ductwork systems
|62 Electricity production system
|63 Electricity power system
|64 Telecommunications system
|66 Systems for voltage regulation and electrical separation
|67 Systems for electrochemical protection of installations, etc.
|7||TRANSPORT SYSTEMS ETC.
|70 Composite transport systems
|71 Lift systems
|73 Escalator and moving pavement systems
|75 Service systems for material and item transport
|76 Control and drive systems for machine driven gates, doors, etc.
|8||CONTROL AND MONITORING SYSTEMS
|80 Composite control and monitoring systems
|81 Control and monitoring systems for property management
|82 Control and monitoring systems for process installation
|83 Control and monitoring systems for transport installation
|84 Control and monitoring systems for treatment and transport of waste
|85 Control and monitoring systems for energy provision systems
|86 Control and monitoring systems for electricity provision systems
|9||OTHER ELEMENTS INCL. OTHER SERVICES ENGINEERING ELEMENTS
|91 Reserved. Recommended place for "Common work and occasional manufacture" in connection with building production
4.1.6 Designed element
According to the ISO Technical Report a designed
element is an element for which the "technical solution
and form of construction" have been determined (ISO 1994
a). For example, an "enclosure" element may be designed
as a construction of gypsum board and studs, then it is defined
as a designed element. In the ISO Technical Report there is no
explicit definition of the concepts "technical solution"
and "form of construction", but from their use it may
be reasonable to assume that the concepts together have a meaning
which includes composition, internal structure, and aspects of
the production activity. To see a part as a "designed element"
is to recognise both the part's characteristic function and its
compositional properties, see Fig. 11 and Fig. 14.
The ISO Technical Report states that the concept
of designed element is of importance for cost information and
product modelling since it includes both functional and material
properties. The concept of designed element represents a combination
of functional and compositional properties of a part. The same
concept should be possible to apply both in standardisation of
technical solutions for specific functions and for classification
of construction products.
4.1.7 Work section
According to the ISO Technical Report a work section
is: "One or several physical parts of a facility, viewed
as the result of particular skills and techniques applied to particular
construction products and/or designed elements during the production
phase" (ISO 1994 a). According to the definition, the concept
work section has reference to the construction work part and its
Wåhlin has shown how the reference of the
concept of work has shifted in the Swedish AMA's back and forth
between work activity, used resources and result (Wåhlin
1986). Although the term 'work section' has connotations to both
activities and results, it mainly denotes the result of the activity,
see Fig. 13. The reason for this is stated in the ISO Technical
Report: "The most useful approach to the classification of
activities is from the point of view of their result, i.e. physical
parts of the facility being constructed". Production activities
and production resources depend on the production methods used,
since the methods are often subject to changes, they might not
be suited for standardisation. It is for many reasons more convenient
to set requirements on the finished result. This may also be a
reason for the shift in meaning of the concept of work section
from activity to result.
FIG. 13: Reference and representation of different
"work section" concepts
A work section is not defined by its function in
a specific facility, it is a construction result characterised
by the used construction products, and their material substance,
and the production activity. Seen as a result, a work section
is a "bottom-up" or compositional view of a physical
part of a construction work. As a result, a single work section
has a function but may not have the characteristic function required
of an element. Combinations of work sections may result in things
with required element properties, see Fig. 14. Work sections of
the same kind may in principle have different element properties,
e.g. out of two concrete walls with the same composition, only
one may be load bearing.
FIG. 14: A work section is the result of production
activities on construction products
The produced result is a construction work part
with certain properties. In BSAB 96 there are other kinds of work
sections as well, e.g. "scaffolding" and "snow-clearance".
These are not physical parts of construction works, but still
necessary for the production process.
4.1.8 Production activity
A production activity uses resources and produces
results. The resources are construction products, construction
aids and human effort (labour and thought), the results are both
physical parts of construction works and other things or processes
necessary during production (ISO 1994 a).
A producer might be viewed as a system that acts
with production activities on the construction products to produce
construction work parts. Production activities are particular
skills and methods in work which transforms and assembles particular
construction products into so called "work sections",
results, e.g. "work of clay brick in building", and
"window". The aim of the production activity is to achieve
work sections with "element"-properties, see Fig. 14.
4.1.9 Construction product
Construction products are defined as: "Products,
components and 'kits of parts' incorporated or intended for incorporation
into facilities, including furniture and equipment" (ISO
1994 a). Construction products are things with the purpose to
be used as, or transformed into, parts in construction works,
e.g. in situ-concrete. Construction work parts and construction
products may have the same composition and internal structure,
the main difference is that the former is produced on site while
the latter is produced "off site" with the intention
to be assembled on the site.
A classification of construction products has been
done by a working group organised by EPIC, the European Product
Information Co-operation (EPIC 1993). Construction products are
grouped according to main function, shape and constituent material
or products, see Fig. 15.
FIG. 15: Construction product as a system
4.1.10 Construction aids
Construction aids are defined as: "Scaffolding,
formwork, machines and tools (including required energy), consumable
stores, construction products used for temporary structures and
facilities, and other objects needed for the purposes of the construction
process which are not incorporated into and do not furnish or
equip the facility", (ISO 1994 a). Construction aids are
parts of the production system, see Fig. 14.
A specific table for attributes can be of use for
"internal arrangement of technical documents, structuring
of product data bases, structuring of other classification tables
according to primary attributes, and definition of requirements
for projects and resources generally" (ISO 1994 a). The CIB
Master List is a list of attributes used for the arrangement and
presentation of information in technical documents for design
and construction (CIB 1983).
In Fig. 16, the attributes are related to the property
model presented in section 2.3.1. The attributes represent factual
or phenomenal and intrinsic or mutual properties that the construction
work has either by itself or in relation to some other thing,
for example a user or a reference frame. The types of attributes
that are of interest to the construction industry are: performance,
function, shape, location, material, price, and production time
(ISO 1994 a).
FIG. 16: Attributes related to the property model
Shape attributes and material attributes are compositional,
that is they are factual, intrinsic properties. The performance
attributes that are mentioned in the ISO Technical Report are
functional, that is factual, mutual properties that emerge in
bonding relations to the environment. The concept "performance
property" in the ISO Technical Report is used with the same
meaning as the concept "function property" in this paper.
In other contexts performance is a measure of relative
quality, it relates a thing's properties to some standardised
reference frame. Performance used with this meaning is a comparison
relation and thus non-bonding. The function attributes in the
ISO Technical Report are in fact not intrinsic properties of construction
works, but properties of the composite system of construction
works and users. Terms like transport, industry and commerce stand
for activities of these socio-technical systems.
The location and production time attributes are
factual mutual properties in non-bonding relations to environmental
reference frames for space, time and computation. Price attributes
and other often needed "administrative" attributes like
name or id are phenomenal properties in relation to information
handling social or socio-technical systems.
5 CLASSIFICATION FOR PRODUCT MODELLING
5.1 Design object
Representations of factually possible construction
works are created in the design process. During design, properties
are determined incrementally, the designer works on a "design
object" that is increasingly more specified. If the design
object models a building part, it may initially represent something
space-dividing which is later decided to be a wall. Then properties
are determined for proportions between wall and window, wall material,
wall thickness, sound insulation, surface material etc., see Fig.
The functional demands on the physical parts of
the construction work most often require technical solutions where
several smaller parts interact in systems of varying complexity.
Complex properties may not be held by one single part, but several
parts must interact to achieve the wanted function, e.g. the wall
function or the floor structure function. The parts that make
up a system like a wall, may have different spatial extension,
e.g. the floor carpet may be extended up on the wall to make a
skirting and the vapour barrier may be continued inside the ceiling,
on the outside the brick work may extend as one work section all
over the facade. The impression is a collage of overlapping units.
This is especially significant to on site construction while prefabricated
units must have a more unified extension.
The design object must be able to accommodate the
growing complexity without ad hoc solutions, the basic structure
of the object must allow successive composition of new parts as
well as decomposition into separate units (Eastman 1994). It is
also an advantage if the same object structure can be used throughout
the whole design process from inception and brief to production
planning and real estate management.
If a design object has the properties sketched above
it is not critical what level of composition the initial design
object represents, it is possible to start the design process
with a very simple object representing only a spatial extension
of some object e.g. some enclosure. In the early stages of the
design process where the emphasis is on the use and experience
of the facility, design objects may represent spatial properties
of physical parts like wall, floor, roof, window, door, etc. Different
design objects may be distinguished in order to be able to represent
physical parts with different function and production requirements.
A design object may represent other things than
constructions. There are at least three major kinds of things
that are of interest to represent in the early stages of the construction
design process: organisations, construction works and site (Ekholm
and Fridqvist 1995).
FIG. 17: A construction design object must accommodate
to growing complexity
5.2 Classification and design objects
The need for classification during the design process
is different from that in traditional classification. Other classes
are of interest than those needed for tendering and calculation,
for example. The objects in the beginning of a design process
must be able to have varying functional and compositional properties.
In the earliest stages of the design process it
may be most important to identify classes of parts according to
shape, e.g. horizontal or vertical plate, circular or rectangular
beam or column etc. (Tarandi 1994). The location in the construction
and other properties can be assigned in the sequence the designer
finds relevant. This implies that a classification of parts in
the earliest stages of the design process could be done by a shape-facet.
In the design proposal stage it is possible to classify
the design objects as elements according to their characteristic
function and finally in the construction drawings stage, the design
objects may be classified as designed elements composed of separate
work sections seen as construction results, see Fig. 18.
FIG. 18: Example of tables for classification
of parts during different stages in the design process
It seems reasonable that the collection of parts
in a building project can be classified according to a series
of different classifications. Objects with a certain property
may be retrieved separately from the database in a computer-aided
design process. In this way traditional building classes as well
as other relevant classes like fire resistance, sound insulation
etc. can be organised. The only requirement is that these new
properties can be classified in a standardised way, and added
to the design object during the process.
6 CONCEPTUAL SCHEMA OF CONSTRUCTION WORKS
6.1 Framework for building information in the ISO Technical
The different concepts discussed in previous sections
belong to a framework for construction works information. A schema
is presented in the ISO Technical Report that relates basic concepts
for describing construction works, see Fig. 19. The schema shows
a level order with buildings in the highest level followed by
the levels of elements, work sections and construction products
in successively lower levels. These are all seen as produced physical
objects with examples of different attributes listed. The schema
is developed according to the NIAM information modelling technique
(Nijssen G.M. and Halpin T.A 1989).
FIG. 19: Schema in the ISO Technical Report relating
basic construction information concepts
The ontological starting points in this paper lead
to a somewhat different schema than ISO's. In this study an element
is identified through a "top-down" functional view on
the part, and a work section is identified through a "bottom-up"
compositional view on the same part. A complete description of
a part includes both its element and work section properties.
The definitions of element and work section in the ISO Technical
Report are in accordance with the ontological starting points
of this study. However the schema in Fig. 19 shows a different
conception where a work section is a part of an element and a
construction product is part of a work section.
6.2 Framework for construction works information
This section presents a conceptual schema for construction
works that relates some of the basic concepts discussed here,
see Fig. 20. This schema is presented in EXPRESS-G, a graphical
notation technique of the EXPRESS information modelling language.
EXPRESS is the official information modelling language within
STEP, and an international standard (ISO 1994 b), also described
in (Schenck and Wilson 1994).
The concrete functionally distinguishable things
that are produced in the construction process, namely the construction
artefacts, are infrastructure units, construction works, construction
work elements, element parts, and spaces. These construction artefacts
have properties of specific interest to the construction process
like production time, price, function, etc. The functions of a
thing are the relations to its environment, for example the site
and the users.
FIG. 20: Level order and main properties of construction
Infrastructure units are aggregates of construction
works used by a social organisation for a specific purpose, for
example the construction works of a university campus or an airport.
An infrastructure unit is characterised by its spatial pattern.
Construction works are concrete systems composed of construction
work parts of different complexity, from simple to complex units.
Spaces are aggregates of construction works, their parts and other
things with certain spatial and functional properties.
Infrastructure units, construction works and their
parts make up a composition level order of increasing complexity
with the levels:
- infrastructure unit (town, village, university campus etc.)
- construction works (streets, houses, canals, bridges etc.),
- construction work elements (column, wall, duct etc.)
- element parts (wooden studs, gypsum sheets, etc.).
In this level ordering, the element parts constitute
the lowest level. Each physical thing that is assembled in its
place in the construction is by definition a part, it has properties
that contribute to the properties of the construction work as
a whole. However, to build a more complex part that has the characteristic
function of an element it may be necessary to combine one or many
atomic parts, for example the wooden studs and gypsum sheets that
together make up the element wall. This is recognised in the Nick
information model (Löwnertz and Tarandi 1994, Tarandi et
The question of levels within the collection of
construction work parts is not elaborated further in this paper
since the subject deserves a separate study. An interesting question
is whether the most complex systems of parts belong to the level
of construction works or constitute a separate level of parts.
It can be argued that the loadbearing, enclosure and servicing
properties characterise the construction work as a whole. A theoretical
study of the level structure of construction works is presented
by Ekholm (Ekholm 1987 and 1994). In building product modelling,
the RATAS Model, (Björk 1989), and the AEC Building Systems
Model, (Turner 1990), are examples where a level order is presented.
Construction work parts are assembled and transformed
construction products. The construction process uses the resources
construction products, construction aids, and human effort (i.e.
worker's labour and thought) and produces results that are both
parts of construction works and other things and processes necessary
for the production process. To analyse a part as work sections
is a compositional view of the part. It includes aspects of the
production activities and used resources including construction
products and their constituent material.
7 Conclusions of the study
This study has applied basic concepts in semantics
and ontology to build a framework for construction works classification.
The conclusions of the study are partly of a general character,
and partly concern the continued work with the ISO Technical Report.
The study has aimed at relating traditional and
pragmatically-developed concepts in construction classification
to an ontological theory of properties. This theory has been used
as a tool to analyse the traditional classification concepts and
to give them and their relationships a precise meaning. The work
has both confirmed and questioned the meaning of traditional concepts.
The introduction of the idea of "views" on the physical
parts has been valuable to explain both the element and work section
concepts as functional respectively compositional views. Finally
the traditional classification concepts are related in a generic
conceptual schema of construction works.
Other researchers for example Vanier (Vanier 1994)
have recognised the need for a conceptual framework as a background
for building a classification system. He has found that in conceptual
modelling, as a means to represent real world objects and their
relationships, the favoured method by many researchers is an object-oriented
approach. However object-oriented modelling does not claim to
rest on a general property theory, see for example (Rumbaugh et
al 1991). A hypotheses worth testing is that Bunge's ontological
theory (Bunge 1977) could enrich and contribute to a further development
of object-oriented modelling.
Among the more specific conclusions are those that
relate directly to the ongoing work within ISO TC59/SC13 with
the classification framework presented in the ISO Technical Report:
- The conceptual framework for construction works presented
in the ISO Technical Report must be further developed and clarified
to support the international work on development of classification
tables in ICIS and STEP.
- A separate classification of socio-technical user systems
may be a useful background for classifying infrastructure units,
construction works and spaces according to the activities they
- The classifications of infrastructure units, facilities and
spaces in the ISO Technical Report are based on functions in use.
A classification based on intrinsic properties is also feasible
and should be considered.
- A new definition of "space" that recognises its
material boundaries is required.
- The difference between element concepts based on direct and
combinatory grouping needs to be recognised in the ISO construction
- Classification of parts for the early stages of the design
process has a different purpose than traditional classification,
which is aimed for the later stages of the process. A classification
table for "shape objects" is needed for CAD in the early
stages of the design process.
I am grateful to the following persons who in different
ways have contributed to the project: Professor Bo Christer
Björk at the Royal Institute of Technology, KTH in Stockholm
initiated this project and contributed with valuable advise. Henry
Karlsson, Technical Manager at the Swedish Building Centre, made
it possible for me to participate at the meetings of ICIS WG3
and ISO TC59/SC13/WG2. Lars Häggström, project leader
for the BSAB 96 system at the Swedish Building Centre, has
been an invaluable source of information and comments during the
whole project. I am also grateful to Professor Lars-Magnus Giertz,
originator of the Swedish SfB system for his advise, and to Sverker
Fridqvist LTH, Kjell Svensson KTH, Väino Tarandi KTH, and
Dana Vanier NRC for comments on the manuscript. However I am solely
responsible for the final result. The project was financed by
BFR, the Swedish National Council for Building Research and NUTEK,
the National Board for Technology Development.
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Available electronically at http://itcon.fagg.uni-lj.si/~itcon/