Abstract
Practical workflow systems need to be able to tolerate deviations from the initial process model because of un-anticipated situations. They should also be able to accommodate deviations in the format of the forms and data being manipulated. We offer a framework for treating both kinds of deviations uniformly, by applying ideas from programming languages (with workflow agents as potential on-line exception handlers) to workflows that have been reified as objects in classes with special attributes. As a result, only a small number of new constructs, which can be applied orthogonally, need to be introduced. Special run-time checks are used to deal with the consequences of permitting deviations from the norm to persist as violations of constraints.