InConcert is an object-oriented client-server workflow management system. An overview is provided of the functionality of InConcert and how it is implemented on an underlying relational database management system. Data management issues in supporting distributed workflow are briefly reviewed.

Workflow management is a technology that is considered strategically important by many businesses, and its market growth shows no signs of abating. It is, however, often viewed with skepticism by the research community, conjuring up visions of oppressed workers performing rigidly-defined tasks on an assembly line. Although the potential for abuse no doubt exists, workflow management can instead be used to help individuals manage their work and to provide a clear context for performing that work. A key challenge in the realization of this ideal is the reconciliation of workflow process models and software with the rich variety of activities and behaviors that comprise “real” work. Our experiences with the InConcert workflow management system are used as a basis for outlining several issues that will need to be addressed in meeting this challenge. This is intended as an invitation to CSCW researchers to influence this important technology in a constructive manner by drawing on research and experience.

A replicated directory management algorithm is presented that supports full location-transparency by allowing migration and reconfiguration at the granularity of individual names. Initially, all names in a directory (including names not yet in use) are controlled by the same set of sites, but control over any individual name (or range of names) can be migrated, e.g. to the set of sites that control the data object associated with the name. The method is based on a directory replication algorithm of J.J. Bloch et al. (1987), incorporating two extensions: (1) allowing control over individual names in a directory to migrate independently; and (2) allowing the definition of relationships among names, such that if control over a given name migrates, then those names that depend on it are automatically migrated as well. Finally, it is stated that the major cost of the algorithm, compared to simpler approaches that do not provide the same degree of location transparency, is the additional complexity and difficulty of obtaining a consistent view of the entire directory.>

Data sharing is fundamental to computer-supported cooperative work: People share information through explicit communication channels and through their coordinated use of shared databases. This paper examines the data management requirements of group work applications on the basis of experience with three prototype systems and on observations from the literature. Database and object management technologies that support these requirements are briefly surveyed, and unresolved issues in the particular areas of access control and concurrency control are identified for future research.

A replicated database architecture is described in which updates processed at a site must be saved to allow reconcilliation of newly arriving updates in a way that preserves mutual consistency. The storage space occupied by the saved updates increases indefinitely, and periodic discarding of old updates is needed to avoid running out of storage. A protocol is described which allows sites in the system to agree that updates older than a given timestamp are no longer needed and can be discarded. This protocol uses a "distributed snapshot" algorithm of Chandy and Lamport and represents a practical application of that algorithm. A protocol for permanent removal of sites is also described, which will allow the discarding of updates to continue when one or more sites crash and are expected not to recover.

Data sharing is fundamental to computer-supported cooperative work: 'people share information through explicit communication channels and through their coordinated use of shared databases. Database support tools are therefore critical to the effective implementation of software for group work. This paper surveys data sharing requirements for group work, highlighting new database technologies that are especially likely to affect our ability to build computer systems supporting group work.

An overview is presented of an approach to distributed database design which emphasizes high availability in the face of network partitions and other communication failures. This approach is appropriate for applications which require continued operation and can tolerate some loss of integrity of the data. Each site presents its users and application programs with the best possible view of the data which it can, based on those updates which it has received so far. Mutual consistency of replicated copies of data is ensured by using time stamps to establish a known total ordering on all updates issued, and by a mechanism which ensures the same final result regardless of the order in which a site actually receives these updates. A mechanism is proposed, based on alerters and triggers, by which applications can deal with exception conditions which may arise as a consequence of the high-availability architecture. A prototype system which demonstrates this approach is near completion.

A principal impediment to the use of declarative assertions for monitoring the state of a dynamic database is the high cost of conventional implementation techniques for such a facility. This paper presents a means of efficiently detecting violations of assertions caused by updates to a database. Our technique is based on the premise that the structure of updates to a database can generally be anticipated, and that an analysis of the potential effect that an update may have on an assertion can enable the assertion to be efficiently tested when the update is performed.This analysis is performed by a compile-time assertion processor; for each type of update operation defined on the database, the assertion processor synthesizes a procedure that will be used to evaluate a set of given assertions whenever an operation of the given type is performed on the database. For each assertion and operation, the assertion processor performs a detailed logical analysis, called perturbation analysis, of the effect that the operation may have on the assertion. Perturbation analysis identifies conditions that can be efficiently tested at run-time (when an operation of the given type is performed) and that minimize the extent to which the assertion must be fully reevaluated; the identified conditions also enable the assertion to be tested before the update is actually performed, thereby avoiding the need for expensive back-out procedures in the case that the assertion is found to be violated. Based on this analysis, the assertion processor generates a set of alternative efficient means of determining whether or not execution of the operation causes the assertion to be violated. A database transaction processor, which estimates the performance cost of each of the alternatives in the context of the physical representation and access methods of the database, can then be used to identify the least expensive means of testing the assertion.This work has been done in the particular context of semantic integrity assertions, but it readily extends to related problems of database monitoring. The efficiency of testing that can be achieved through the use of our assertion processing technique in comparable with that attainable through the use of hand-coded procedures. The technique therefore supports all the advantages of the declarative approach to database assertion-monitoring, while retaining the level of efficiency that is usually associated with procedural methods.