An initial answer to these problems was the attemp to create interfaces between data processing applications. Substantial progress has been made in the communication with internet protocols and browser interfaces. In other areas, such as building technical services, several new standards have been introduced and this has prevented the conclusion of these developments. Data interchange formats for geometric and graphical information (example drawing interchange format, dxf) are not comprehensive or reliable enough, which has always limited their use in the design process. There has been a need for universal interfaces for 20 years, which was reasonably well satisfied with introduction of STEP (Standard Exchange Procedures). In contrast to industrial products, which consist of a number of relatively independent individual components, buildings are more complex, as they have to satisfy many, often conflicting, requirements, have a long service life and a large number of stakeholders are involved in the planning and design process. The complexity of this process is made even more so by many feedback loops and incomplete or imprecise information.
As geometric aspects dominate in the building industry, it has so far not been possible to develop a general drawing-oriented data structure.
Researchers have certainly continued to develop proposals for this, such as transferring the ideas of product modeling into the building industry, but their implementation in practice and the development of suitable software have not been successful. In principle there are several possibilities for solving the problem of inadequate interoperability of the tools, including:
– A universal interface that links all programs with one another.
– A central inferface in the form of an abstract model to which all applications can refer and through which they can communicate with one another.
One such central interface is the building information model (BIM), which is also called the building product model. This model consists of a semantic computer-readable description of a building.
A building is divides into objects that are assigned attributes (properties) and relationships with other objects. All such objects, which are designated as classes, form the Industry Foundation Classes (IFC) and are the current international standard of the large CAD software publishers who are members of the international Alliance for Interoperability.
In this product model an entity “window” (ifcWindow) contains all the information about a window necessary to describe it, in theory over the complete life cycle. The attributes of the entity “window” (type, dimensions, components, U-value, cost…) are unambiguously described in a forma manner and are used for interchanging information between different applications.
For each phase (example preliminary design) and specialist discipline (architect…) there is a separate view on the object window. An application program for calculating the heat requirement of a building obtains the initial values for its calculation through the central document management systems (DMS) from the building information model and exports the results again through the DMS to a graphical interface, which displays the performance of the building at a specific point in time. All the important properties of a building are stored in the building’s document management system (DMS) and can be archived or displayed in any number of ways. The central file storage facility always displays the latest version. Earlier versions are also stored there.
The important advantages and possibilities are:
– complete separation of content and form of information.
– Contradiction-free, complete, up-to-date, continuously secure data.
– Ability to check the consistency of the project using the model (example check of standards).
– Ability to query the model.
– Immediate determination of the effects of a change in one element/property on other elements/properties.
– Ability to display the same basic data in any number of different ways.
– Ability to develop a number of fairly sophisticated tools in a very short time and make them available to a large circle of users. The tools only have to be compatible with a comprehensive interface (IFC) and are no longer dependent on having particular versions of particular programs.