MASTER/DOCTORATE IN COMPUTING : Exception handling for information and software systems

Exception modelling is often neglected or left to the rela application. Languages such as ADA have had already an explicit exception modelling and handling concept. Languages such as Java or modellling languages such as BPMN leave to exception handling to a global exception handler. Instead the programmer should model and program the exception handling in an explicit form as an orthogonal component. We claim that exception modelling and handling can be based on experience the database community has gained over twenty years with handling of data integrity. In databases exception handling is handled by models, by control facilities, by interaction of exception handlers with schedulers, and by specific supporting programs.

The concept of exception has been defined in diverse ways.  We relate exceptions to computational transactions and to control constructs.  Our view of a transaction is very broad, and we consider transactional exceptions to be instances of undefined function values.  By giving different interpretations to ``undefined'' we arrive at a classification of transactional exceptions.  Our primary interest is in information systems, i.e., in database transactions, and in processes that consist of such transactions.

In the database context we show that liberal treatment of exceptions is simpler than total quality management for consistency based on a set of constraints.We refer to control operations that link transactions into processes as actions.  Actions tend to be time-related, and time Petri nets provide actions with semantics.  The time Petri net representation indicates where exceptions can arise. We also consider high-level monitors for the detection of exceptions.  Although our emphasis is on detection of exceptions, their handling is also discussed.