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Dagstuhl Seminar 9305

Versioning in Database Management Systems

( Feb 01 – Feb 05, 1993 )

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Please use the following short url to reference this page: https://www.dagstuhl.de/9305

Organizers
  • G. Vossen
  • K. Vidyasankar
  • W.S. Cellary



Motivation

Versioning of data refers to the ability of a database management system to create, organize, manage and maintain distinct versions of individual data items or objects over certain periods of time. In traditional database systems, versioning can be employed to improve the efficiency of transaction synchronization through the provision of multi-version concurrency control algorithms. While traditional systems emphasize the view of keeping versioning transparent from a user's point of view, i.e., having a user ignore that data objects may exist in multiple versions in the database, more recent applications of database systems have among their requirements that the versioning mechanism of the system has to be apparent to users. For example, temporal databases, which organize data across time, need to keep track of how data objects change over time (e.g., a person's employment history) and to answer historical queries (e.g., "what was a person's position ten years ago"). Moreover, in design environments as given in a computer-aided design (CAD) or software engineering (CASE) context, users need to experiment or simply work with different versions of the same object, in order to explore distinct evolution paths of the object under design, or to accommodate multiple composition requirements. Here, the situation is further complicated by the fact that design objects are typically of complex structure, with references to many subobjects each of which can itself be multi-versioned. In addition, these versions typically even represent objects which are not yet completed, and which are used by a group of cooperating designers. To support such a cooperation, versioning must be complemented by mechanisms to create configurations of potential final design objects.

Since especially in non-traditional applications of databases a versioning facility has been recognized as important and must be provided at the user's level of abstraction, a number of different aspects of versioning has been investigated over the past ten years. In particular, the questions that have been addressed include

  1. version models which provide data structuring concepts for organizing versions into derivation histories, for composing complex objects from versions of their component objects (i.e., for forming configurations), and for tracking equivalent versions across multiple representations of the underlying object,
  2. operational issues including inheritance and derivation, i.e., mechanisms through which new versions can be obtained from existing ones, change notification and propagation describing how complex interconnected design structures respond to changes, and workspace models, i.e., mechanisms through which new versions become visible to and sharable by a designer community,
  3. organizational frameworks for group cooperation, which add an appropriate layer of abstraction to a versioned database,
  4. language concepts through which users can conveniently and adequately employ an apparent versioning mechanism,
  5. implementation aspects including storage structures for versions and their histories, transaction processing in the presence of versions and/or workspaces (and distributed system architectures), consistency preservation for configurations and multiple representations.

The work that has been done on versioning in databases in recent years shows that a number of issues is still not well-understood, although commercial products supporting versioning are already available in the marketplace. For example, the perception that a versioning facility should be orthogonal to both object composition and concurrency control has only recently been advocated. By the same token, a unification or even standardization of approaches is rarely in sight. Finally, the proper meaning, implications of and requirements to versioning in distinct application domains (including, CAD, CASE, office information systems, or multimedia systems) are neither fully understood nor exhaustively explored.

Given this situation, it was the goal of this workshop to bring together, to the organizers' knowledge for the first time separate from a major database conference or workshop, people from the international research community who have made important contributions to versioning and/ or are still actively working on this subject. Furthermore, it was our intention to identify commonalities among the variety of proposals that have been made in the past, and to isolate demanding open problems in this field.

The meeting brought together 28 scientists from the eight countries of Brazil, Canada, Croatia, France, Germany, Italy, Poland, and USA (see last section). During the week, 20 presentations spanning a wide range of issues were given in a dynamically composed program, with plenty of discussion time after each; in addition, an open discussion was held on Thursday afternoon and evening.

We felt that all participants enjoyed the workshop, and we wish to thank the Dagstuhl staff for ensuring that everything ran so smoothly. The Dagstuhl office in particular provided financial support for the participants from the Central European countries, thereby enabling them to travel to the castle and to attend the workshop, which is gratefully acknowledged. Special thanks go to the kitchen staff for keeping us stuffed with good food all the time, and to Melanie Spang for her patience in handling everything that came up during the week.

Copyright

Participants
  • G. Vossen
  • K. Vidyasankar
  • W.S. Cellary