The curriculum of the Faculty has been radically revised over the last two years and is now based on the concept of "Problem-Based Learning". The subject matter taught is divided thematically into specific issues that are taught in six week blocks. The vehicles for these blocks are specially selected and adapted case studies prepared by teams of staff members. These provide a focus for integrating specialist subjects around a studio based design theme. In the case of second year this studio is largely computer-based: many drawings are produced by computer and several specially written computer applications are used in association with the specialist inputs.

This paper describes the "block structure" used in second year, giving examples of the special computer programs used, but also raises a number of broader educational issues. Introduction of the block system arose as a method of curriculum integration in response to difficulties emerging from the independent functioning of strong discipline areas in the traditional work groups. The need for a greater level of selfdirected learning was recognised as opposed to the "passive information model" of student learning in which the students are seen as empty vessels to be filled with knowledge - which they are then usually unable to apply in design related contexts in the studio. Furthermore, the value of electives had been questioned: whilst enabling some diversity of choice, they may also be seen as diverting attention and resources from the real problems of teaching architecture.

When trying to understand how designers work, it is tempting to examine design products in order to come up with the principles or norms behind them. The problem with such an approach is that it may lead to a purely syntactical analysis of design artifacts, failing to capture the knowledge of the designer in an explicit way, and ignoring the interaction between the designer and the evolving design. We will present a theory about design activity based on the observation that knowledge is brought into play during a design task by a process of interpretation of the design document. By treating an evolving design in terms of the meanings and rules proper to a given way of seeing, a designer can reduce the complexity of a task by focusing on certain of its aspects, and can manipulate abstract elements in a meaningful way.

Assuming the availability of a more general building data model, one must define life and fire safety features of a building before any automatic checking can be performed. Object oriented data structures are beginning to be applied to design objects, since they allow the type versatility demanded by design applications. As one generates a functional view of the main data model, the software user must provide domain specific information. A functional view is defined as the process of generating domain specific data structures from a more general purpose data model, such as defining egress routes from wall or room object data structure. Typically in the early design phase of a project, these are related to the emergency egress design features of a building. Certain decisions such as where to provide sprinkler protection or the location of protected egress ways must be made early in the process.

One cannot conduct such studies on real cities except, perhaps, as a point of departure at some specific point in time to provide an initial layout for a city knowing that future forms derived by the studies will diverge from that recorded in history. An entirely imaginary city is therefore chosen. Although the components of this city at the level of individual buildings are taken from known cities in history, this choice does not preclude alternative forms of the city. To some degree, building types are invariants and, as argued in the Appendix, so are the urban typologies into which they may be grouped. In this imaginary city students of urban history play the role of citizens or groups of citizens. As they defend their interests and make concessions, while interacting with each other in their respective roles, they determine the nature of the city as it evolves through the major periods of Western urban history in the form of threedimensional computer models.

My colleague R.J. van Pelt and I presented this approach to the study of urban history previously at ACADIA (Seebohm and van Pelt 1990). Yet we did not pay sufficient attention to the manner in which such urban models should be structured and how the efforts of the participants should be coordinated. In the following sections I therefore review what the requirements are for three-dimensional modeling to support studies in urban history as outlined both from the viewpoint of file structure of the models and other viewpoints which have bearing on this structure. Three alternative software schemes of progressively increasing complexity are then discussed with regard to their ability to satisfy these requirements. This comparative study of software alternatives and their corresponding file structures justifies the present choice of structure in relation to the simpler and better known generic alternatives which do not have the necessary flexibility for structuring the urban model. Such flexibility means, of course, that in the first instance the modeling software is more timeconsuming to learn than a simple point and click package in accord with the now established axiom that ease of learning software tools is inversely related to the functional power of the tools. (Smith 1987).