Current trends in exception handling

Abstract

1 THE ARTICLES THE second part of this special issue on Current Trends in Exception Handling includes four papers which primarily deal with exception handling in human-centered systems such as workflow, requirements specification, and new interactive programming models such as spreadsheets. These research contributions demonstrate that exceptions are not restricted to programming languages, but occur in many, if not most, real-world situations. These papers also reflect that exceptions can be deviations from normal conditions and may not necessarily imply errors. This is similar to Goodenough's observations in his classic paper in the 1970s [1]. These papers lead us to observe that anything that has an algorithmic flow, whether it be workflow or a design process or a program, has a pervasive exception handling need. Programming may be the ultimate in an algorithm, so many of the problems encountered there have analogies in other areas. Moreover, the computation model presented by programming languages tends to be relatively more simple in regard to handling of exceptions in contrast to dealing with such problems in large-scale systems such as enterprise-wide workflow. In those environments, it is not simply exception handling language constructs that are needed, but a methodology on how to use exception handling. The programming model of spreadsheet systems raises many unique issues related to exception handling. This is a widely used model of programming by end users through the use of many commercial products. In the paper aException Handling in the Spreadsheet Paradigm,o Margaret Burnett, Anurag Agrawal, and Pieter van Zee discuss these issues and present an approach for handling exceptions in this programming paradigm. Many spreadsheet programs can be quite large and complex and, therefore, both reliability as well maintainability of such programs becomes an issue when exception handling is introduced. The authors present their experience with and analysis of the error value models for spreadsheet programs. Achieving a high level of fault tolerance is one of the main concerns in developing modern workflow systems due to many factors: Distributed environment, long duration of activities, and complexity of the software involved are among them. The paper aException Handling in Workflow Management Systemso by Clause Hagen and Gustavo Alonso describes an advanced fault tolerance mechanism for incorporating both transactions and exception handling into such systems. The approach is unique for workflow systems as it treats workflow support as a programming environment and relies on general research on developing fault-tolerant software. The authors use fundamental research on linguistic issues of exception handling and propose simple ways of applying these concepts to transactional workflow management. The modeling language incorporates special features for error detection and handling which are conceptually similar to exception handling features found in programming languages. Another important way in which this approach is new is how it combines transaction atomicity and exception handling. A validation technique is developed to make it possible to assess the correctness of workflow specification in situations when exceptions are raised and handled. In the paper aHandling of Irregularities in Human Centered Systems: A Unified Framework for Data Processes,o Takahiro Murata and Alex Borgida address exception handling problems in human-centered systems. In such systems, exception handling is required for dealing with errors, as well as deviations, in data as well as processes, from their normal constraints. The paper focuses on exception handling in enterprise workflow systems. Generally, in enterprise systems, process models are used for describing the dynamic nature of activities of humans and semi-automated system entities. Most often, such models do not capture many unanticipated deviations. Sometimes such deviations have to be corrected and other times they are to be tolerated. This paper presents a unified model for handling errors and deviations, which are treated as exception conditions resulting from violations of some specified constraints. When permitting deviations to persist, it relies on runtime checks for assessing their consequences. Axel van Lamsweerde and Emmanuel Letier address the issues of aHandling Obstacles in Goal-Oriented Requirements Engineering.o The requirements elicitation process often results in goals, requirements, and assumptions about the desired system that are too idealized and that do not take into account the various kinds of problems that can occur. Not anticipating exceptional behaviors results in unrealistic, unachievable, or incomplete requirements specifications. This, in turn, leads to systems that are not robust enough and which may fail at critical times, perhaps with critical consequences. The authors present formal techniques for IEEE TRANSACTIONS ON SOFTWARE ENGINEERING, VOL. 26, NO. 10, OCTOBER 2000 921