Project duration: January 1999 through September 2004 (Post-doc project)

Collaborative Modeling Systems are distributed, multiple-user systems that provide a team of geographically dispersed designers with the appropriate modeling tools for working together, concurrently and synchronously, on the design of a product. Such tools are especially helpful in current multi-disciplinary design teams, where different members have dissimilar views of the product according to their life-cycle activity (e.g., design, manufacturing planning, assembly planning, inspection planning). Effectively improving the collaboration within such teams can significantly reduce product cost and time to market. We believe that a multiple-view feature modeling system is the ideal basis for a collaborative modeling system.

Our research in collaborative feature modeling is currently focused, among other things, on the following crucial issues:

• concurrency, which deals with the problems of simultaneous access and manipulation of model data by different users;
• synchronization, which deals with the propagation of evolving data among system users, in order to keep their model data consistent;
• interactivity, which deals with visualization and user interaction facilities, aimed at guaranteeing an effective collaboration among system users.

Techniques being investigated within this project are implemented and tested in the collaborative feature modeling prototype system webSPIFF. This system presents a web-based client-server approach, where the server coordinates the collaborative session, maintains the shared model, and provides all functionality that cannot, or should not, be implemented on the client. The clients perform operations locally as much as possible, and only high-level semantic messages, as well as a limited amount of information necessary for updating the client data, will be sent over the network.

Results of this research project are described in a number of publications.

Project duration: January 1995 through December 1998 (PhD project)

Current feature-based modelling systems are still too tied to methods and techniques of conventional geometric modellers. They strongly rely on a history-based approach of the modelling process, with the consequent drawbacks in raising the level of assistance expected from feature technology. Among other pitfalls, the specification and maintenance of feature semantics is not well covered by such systems, and the semantics of modelling operations not well defined.

A complete solution to these problems poses a number of requirements at various levels of a feature modeller. Among them, the following goals are covered within the scope of this research work.

Feature libraries should include declarative specifications of feature classes, each of which contains a full description of the specific semantics desired for its feature instances. The feature model should be fully specified as a set of feature and constraint instances, related by their mutual attach and positioning constraints.

The semantics of all modelling operations should be clear and unambiguous, through the consistent use of references to model features and their elements, instead of to geometric model topologic entities.

Each modelling operation should be monitored, in order to assess the conformity of each feature in the model with its validity criteria. In particular feature interactions, caused by intersections of two or more features in a way that affects their functional or technological semantics, should be handled. Additionally, every validity violation should not only be detected but also be documented, reported to the user, possibly with context-sensitive system hints, and corrected.

As a consequence of the former, the structure of the model, as well as the interpretation of its evaluated geometry, should be completely and unambiguously determined without invoking any model history considerations. Additionally, the re-evaluation of the geometric model after each successful modelling operation should be limited in scope, in order to keep its complexity independent of the number of features present in the model.

Results of this research project are described in the PhD thesis "Validity Maintenance in Semantic Feature Modeling", and in a number of publications. This research has been developed and validated within the SPIFF system, a multiple-view, feature modelling prototype system developed at Delf University of Technology.