Constraint meta-object: a new object model for distributed collaborative designing

Object databases have been recognized as providing rich data modeling capabilities for the next-generation applications, especially CAD/CAM, software engineering, and multimedia. The core object model consisting of objects, messages and inheritance, however, is not adequate to tackle all the requirements of these applications. Since collaborative activity is one of the key features of next-generation applications, it is essential that the basic object model be extended to support collaborative activity. We propose an object model for collaborative designing based on objects and constraint meta-objects. Each design object has an associated constraint space consisting of one or more constraint meta-objects. The object/constraint meta-object separation achieves a clear distinction between design object and its associated design environment and provides a framework for supporting collaboration among members of a design team. Collaboration is modeled as dependencies among multiple constraint spaces on different nodes, and collaborative activity as design transactions satisfying local constraints and propagating constraints among interrelated constraint spaces. We propose language extensions to C++ for capturing the object/constraint meta-object paradigm. The extensions are implemented using filters, a special mechanism for capturing messages sent to an object. Our model has been applied to the case of a mechanical CAD problem