The Designers' Workbench is a system, developed by the Advanced Knowledge Technologies (AKT) consortium to support designers in large organizations, such as Rolls- Royce, by making sure that a design is consistent with the specification for the particular design as well as with the company’s design rule book(s). Currently, to capture the constraint information, a domain expert (design engineer) has to work with a knowledge engineer to identify the constraints, and it is then the task of the knowledge engineer to encode these into the Workbench's knowledge base (KB). This is an error prone and time consuming task. It is highly desirable to relieve the knowledge engineer of this task, and so we have developed a tool, ConEditor, that enables domain experts themselves to capture and maintain these constraints. The tool allows the user to combine selected entities from the domain ontology with keywords and operators of a constraint language to form a constraint expression. We hypothesize that to apply constraints appropriately, it is necessary to understand the context in which each constraint is applicable. We refer to this as "application conditions". We plan to make these application conditions machine interpretable and investigate how they, together with a domain ontology, can be used to support the verification and maintenance of constraints.