An event/trigger mechanism to enforce complex consistency constraints in design databases

Data objects in engineering applications, especially computer aided design, show highly complex structures and a lot of intricate dependencies. Hence a large amount of variably composed consistency constraints have to be dealt with. Furthermore, long transactions which are typical for CAD result in the need to tolerate inconsistencies over unpredictably long periods of time. The demands on mechanisms to enforce consistency in design database systems thus differ from those in business and administrative applications. Comprehensive consistency of the design data can only be attained by degrees. The time and extent of checking have to be determined dynamically and under control by the user. In the case of consistency violations, flexible kinds of reaction are necessary. In this paper we propose an event/trigger mechanism to enforce consistency in design databases that complements the transaction-oriented mechanisms suitable for traditional applications. The underlying ideas are derived from exception handling in programming languages. We present in detail the requirements to meet and how our concept copes with them. We also present an implementation that provides reasonable performance.