KBDS is a prototype design support system for process engineering. It was created as an experimental vehicle to test and develop ideas about the representation of the design process, and to demonstrate how such a representation can be used to support the design activity. Our starting point is a representation of the design process consisting of three space : one for design alternatives, another for design objectives, and a their structure, behaviour, and alternatives. These have been implemented in a prototype system, and their structure, behaviour, and interaction are described. The implementation is based on two powerful techniques : object-oriented programming, and assumption-based truth maintenance systems (ATMS). The functionally of KBDS is shown through a demonstration based on the sequential development of a separation system and the hierarchical conceptual design of the HDA process. This demonstration shows that the current capabilities of KBDS satisfy many of the requirements of a design support system, and provide a basis for future expansion to satify the others.