Workflow management systems (WFMSs) coordinate the execution of applications distributed over networks. In WFMSs, data inconsistencies can arise due to: the interaction between steps of concurrent threads within a workflow (intra-workflow coordination); the interaction between steps of concurrent workflows (inter-workflow coordination); and the presence of failures. Since these problems have not received adequate attention, this paper focuses on developing the necessary concepts and infrastructure to handle them. First, to deal with inter- and intra-workflow coordination requirements we have identified a set of high level building blocks. Secondly, to handle failures we propose a novel and pragmatic approach called opportunistic compensation and re-execution that allows a workflow designer to customize workflow recovery from correctness as well as performance perspectives. Thirdly based on these concepts we have designed a workflow specification language that expresses new requirements for workflow executions and implemented a run-time system for managing workflow executions while satisfying the new requirements. These ideas are geared towards improving the modeling and correctness properties offered by WFMSs and making them more robust and flexible.

In recent years, numerous transaction models have been proposed to address the problems posed by advanced database applications, but only a few of these models are being used in commercial products. In this paper, we make the case that such models may be too centered around databases to be useful in real environments. Advanced applications raise a variety of issues that are not addressed at all by transaction models. These same issues, however, are the basis for existing workflow systems, which are having considerable success as commercial products in spite of not having a solid theoretical foundation. We explore some of these issues and show that, in many aspects, workflow models are a superset of transaction models and have the added advantage of incorporating a variety of ideas that have so far remained outside the scope of traditional transaction processing.

To properly handle concurrent accesses to documents by updates and queries in information retrieval (IR) systems, efforts are on to integrate IR features with database management system (DBMS) features. However, initial research has revealed that DBMS features optimized for traditional databases, display degraded performance while handling text databases. Since efficiency is critical in IR systems, infrastructural extensions are necessary for several DBMS features, transaction support being one of them. This paper focuses on developing efficient transaction support for IR systems where updates and queries arrive dynamically, by exploiting the data characteristics of the indexes as well as of the queries and updates that access the indexes. Results of performance tests on a prototype system demonstrate the superior performance of our algorithms. Keywords: Concurrency Control, Recovery, Transaction Management, Index Management, Information Retrieval, Optimization, Performance, Digital L...

The notion of hierarchical inconsistency bounds that allows inconsistency to be specified at different granularities-with transactions being at the top of the hierarchy, objects at the bottom, and groups in between-is introduced. The mechanisms needed to control the inconsistency so that it lies within the specified bounds are described. The performance improvement due to epsilon serializability (ESR) is evaluated. Two important observations are made. First, the thrashing point shifts to a higher multiprogramming level when transaction inconsistency bounds are increased. Second, for a particular multiprogramming level and a particular transaction inconsistency bound, the throughput does not increase with increasing object inconsistency bounds but peaks at some intermediate value.>