It has long been recognized that property sets may be defined either generically to form part of the published IFC release or specifically to meet regional, local or even project based requirements. Regardless of how they are published, consistency in the naming and usage of properties is important. By applying the principle of a dictionary, it should be possible to ensure that properties are defined consistently, a particular named property always being used in the same way within the same context through its semantic definition and having consistently defined units.

There was a significant workload in the development of IFC 2x simply in sorting out and coordinating all the properties within property sets so that they were coordinated and consistent. This workload (some months) was with a fairly limited number of property sets/properties. If left uncontrolled, this task will grow in future releases and could place a huge load on the model integration process.

ISO TC59/SC13/WG6 has been working for some time on the development of a standard that can offer significant assistance in resolving the issue. There has been IAI input in the development of the conceptual model on which the standard is based, the conceptual model making use of a number of the constructs within the IFC 2x model. Version 1 of ISO PAS 12006 part 3 was published in 2000. Implementation trials have led to further development of this standard and a revised version has been agreed (meeting in Singapore in March 2002). This standard is entitled ?Framework for Object Oriented Information Exchange? and has as its objective the specification of a framework within which extensible taxonomy definitions can be developed. Put simply, an ?extensible taxonomy definition? allows the meaning of a uniquely identified concept to be added to a dictionary, the concept then being able to be described in multiple languages against a primary reference in English. The benefit is that a populated implementation of the standard provides a multi-language dictionary that accounts for the usage of terms in different places (e.g. the term ?door? in Norway means something slightly different to the usage of the term in the UK; specification of fire resistance in the Netherlands is by a code such as B30 whereas in the UK it is a time duration such as 30 minutes).

IFC model developers and users could draw on an implementation of the standard so that the properties they define in property sets (or even class and attribute names in the explicit model) are defined consistently. It is possible that an implementation might even provide a ?drag and drop? interface for the generation of property sets that would make a developers life even easier. It would certainly make model integration much simpler if the source of property terminology was known and trusted.

This project seeks to harmonize the standard with the IFC model so that it is practically and directly usable in IFC development. In so doing, it has the potential to make developments easier, quicker and of higher quality. The inverse is that the IFC model provides an immediate population to standards compliant dictionaries and that IFC model development offers a rapid resource to their further development and completeness. Harmonization in this case does not imply any change to existing conceptual models. It is intended to find a best way of making the ISO PAS work with IFC and vice versa. This will probably make extensive use of mapping/transformation technology such as EXPRESS-X and/or XSLT.

The importance of this project and the benefits that are perceived from its establishment can be seen from the resolutions made by ISO requesting harmonization and the support to the project from members of the International Classification Information Society (ICIS).

The objective of the project is to have the harmonization fully defined and useful within 12 months so that it is available with IFC 2x Edition 2.

• Define the approach and method by which the IFC model can be harmonized with dictionaries structured according to the ISO PAS 12006 part 3 framework so that IFC model development and use can draw on such dictionaries as a resource.
• Define an approach that enables OIFC model development and use to contribute towards the extension of dictionaries.
• Provide an outline specification for an interface that enables property sets to be developed using populated dictionaries.
• Develop a version of the ISO PAS 12006 part 3 standard as an XML schema definition using the ifcXML language binding.
• Formulate requirements for output of property sets resulting from use of dictionaries according to the IFC property set markup language subset of ifcXML.

• Extensions to the IFC conceptual model.
• Extensions to the ISO PAS 12006 part 3 conceptual model.