Exceptions in Information Systems
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.