||"Some progress has been made in the establishment of agreed product models as the basis of a more open information centric approach to engineering, both in the construction sector and beyond. Specific building related initiatives, such as the CIS and the IFC, have been implemented in software and are now beginning to impact on industry. In common with sectors, these standards have drawn heavily on the work of ISO 10303 (STEP), particularly the EXPRESS data definition language and Part 21 file format.Today, although they may differ widely in many respects, the majority of product model based information standards share a common STEP based technology. It is also true that most are currently aimed at providing file based data exchange between existing engineering applications software, even if many have more revolutionary ambitions. It is already apparent that the longer-term realisation of the more interesting possibilities implicitly requires that future applications software is built round the product model, rather than using translators to create a degree of retrospective compatibility. At the same time current software engineering trends are towards smaller modular component software. It is postulated that a future architecture for engineering applications might accommodate both these ideas by constructing engineering software on a product model based repository that offers the developer a more appropriate window onto the underlying information.The focus of this paper is not on the product model, or on the base functionality that any repository should provide, it is on the nature of the interface that might be provided to the application developer. This also has significant implications for the very nature of contemporary applications software, but this is not addressed in this paper. The main subject of the paper is a description of a proposed architecture that employs a hierarchy of “windows” to present an application with an appropriate view of information objects held in a product model repository. The paper also provides a description of an initial prototype that shows how some of the identified design goals have been realised.The proposed architecture essentially provides a semantic and a syntactical bridge between an object server (or repository) and client applications. It enables a structure of different windows to be defined, each window comprising a population of virtual objects whose definition cascades down to the level below – until the real objects are encountered in the underlying repository. A formal EXPRESS schema is used to specify the semantics of each window, and the services provided by each widow include:·Filtering to exclude specified virtual objects·Mapping to create the virtual objects·Validation to check compliance of virtual objects at each window level·Added value engineering functionality. The paper concludes with some speculative preliminary conclusions on the practical implications of such an architecture being adopted by the construction sector."