BIM is a business process that promotes collaboration between disciplines and this collaboration is ensured by using a common language. The common standard developed by the buildingSMART is the Industry Foundation Class (IFC). It defines an exchange format for information related to a building and its surroundings. The overall mission of the IFC is defined to be “ the specification for sharing data throughout the project life-cycle, globally , across disciplines and across technical applications in the construction and facilities management industries” (www.ifcwiki.org)
Interoperability issues in the AEC industry cannot be easily resolved without a set of rules and principles for classification of information requirements into data exchange specifications. The issues are being deepened by the complexity of the building information models, wide range of specializations and vocabularies in the AEC industry, the increasing amount of computer software applications, and the management practices employed. This paper looks at the IFC, challenges with data exchange rules and formats, while also looking at the future of IFC based interoperability.
The IFC development is faced with two challenges:
1. Provide a data structure that is able to fulfill the information requirements of involved disciplines.
2. Supporting the implementation of a data structure that exceeds the scope of typical domain specific design applications.
IFC is an international standard and has to deal with different cultural backgrounds and languages.
Overview of the IFC development Process
In general, in order to share information, the following three specifications should be in place.
1. An exchange format, defining HOW to share the information. The IFC is such a specification.
2. A Reference Library, to define WHAT information we are sharing. The International Framework of Dictionaries (IFD) serves such a purpose.
3. Information Requirements, defining WHICH Information to share WHEN. The Information Delivery Model (IDM)/Model View Definitions (MVD) approach forms that specification.
The specifications supporting the IFC development have to be defined according to the needs of the involved users. The development of the IFC address four main areas;
1. Business requirement specification
2. IFC extension modeling
3. Use case implementation
4. End user guidance
The IFC development process, in the above order , starts with the requirements and ends with users guidelines.
The need for additional standards
The IFC data model is comprehensive , supporting a wide range of data to be transferred. The IFC allows for various data to be exchanged in various ways, without losing any information. But downstream users usually require specific information that is usually a subset of the Information stored in the IFC. These users would prefer to receive the data they need, rather then the entire data model. The IFC, however, does not capture the methods in which data is created and shared by users. The lack of specific data exchange requirements for different users, also makes it difficult to implement solutions to this problem.
The Information Delivery Manual (IDM)
An Information Delivery Manual (IDM) responds to these problems by proposing a methodology that captures business processes in projects, and developing specifications of detailed user information exchange requirements. The IDM defines, in the language and perspective of the professional participant, what information must be contained in the contracted exchange. The Process maps generated as a result of identifying the IDM, defines selected activities throughout the project delivery process and the information exchanged between them. The IDM is usually developed by domain experts, independent of the data exchange standard. The IDM consists of three parts
1. The Process Maps. – The Process map describes the flow of activities for a particular business process. It enables understanding of the configuration of activities that are required, the users involved , the information required, consumed and produced.
2. The Exchange Requirements – All details of the requirements are described according to business concepts that have to be mapped to IFC or other data structures. This information structures requirements, defining further details about the concepts, highlighting the difference between required ,mandatory and optional information requirements
3. Functional parts and Business Rules. – The functional part is a unit of information used by the solution providers to support an exchange requirement. It is usually a schema in its own right, but also a subset of the full standard on which it is based.
The IDM development process targets both BIM users and solution providers. For users, the IDM define the requirements for the information to be provided and is simple to understand, usually describing the building construction processes. For BIM solution providers, IDMs identify and describe in detail, the functional breakdown of the process and the requirements of the IFC with respect to this process.
The Model View Definition (MVD)
A Model View Definition (MVD) maps the exchange requirements defined above to the IFC , to understand how the exchange of the required data and related constraints can be accomplished using the IFC. MVD tells the software implementer which IFC elements to use, as well as how the implementation should function and what results are expected. MVDs define a logical and coherent subset of the IFC fulfilling a specific use or application type.
The aim of the supporting IDM and MVD processes are to specify exactly which information is to exchanged in each exchange scenario and how to relate it to the IFC model. For Example, an architect designing a building needs to be sure that they receive information from the structural engineer about which walls are load bearing and which are not. At the same time, the structural engineer needs to know the function of each space to calculate the right design loads.
International Framework for Dictionaries (IFD)
Professionals need to work interoperably with each other, while they design and construct buildings. How can a designer be sure that the engineers understand the attributes attached to his design? How can design standards from overseas be incorporated? The IFD creates a catalogue or dictionary of objects and brings together the data into a common view, associating the correct information from a product manufacturer, requirements etc, while also coping with different languages. Put simply, it’s a standard for terminology libraries. The IFD also opens up opportunities for advanced analysis very early in the design. It also allows to create an IFC-BIM for operational and maintenance purposed, while linking existing knowledge systems , product specific data and the IFC – BIM.
How the Standards work together.
Before the users begin to perform data exchanges, the vendors of their favourite software have to implement IFC interoperability ie. The vendors have to enable their software to read and write the IFC format. For repeatability and reliability, this interoperability should support “ contracted exchanges” ie information exchanges that serve a particular transfer. IDM defines the user’s contracted exchanges and the MVD defines the implementations in software.
Once implemented in software, any software should be fully capable of exchanging the required information for the specific process to process scenario. The certification ( by buildingSMART) of the software ensures that the software meets the requirements as specified in the MVD. The software is then tested by users to ensure that the user’s business requirements are fully met by the implemented software capability.