Temporal FDs on complex objects

  • Authors:
  • Jef Wijsen

  • Affiliations:
  • University of Antwerp, Department of Mathematics and Computer Science, Universiteitsplein 1, Wilryk, B-2610, Belgium

  • Venue:
  • ACM Transactions on Database Systems (TODS)
  • Year:
  • 1999

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Abstract

Temporal functional dependencies (TFD) are defined for temporal databases that include object identity. It is argued that object identity can overcome certain semantic diffuculties with existing temporal relational data models. Practical applications of TFDs in object bases are discussed. Reasoning about TFDs is at the center of this paper. It turns out that the distinction between acyclic and cyclic schemas is significant. For acyclic schemas, a complete axiomatization for finite implication is given and an algorithm for deciding finite implication provided. The same axiomatization is proven complete for unrestricted implication in unrestricted schemas, which can be cyclic. An interesting result is that there are cyclic schemas for which unrestricted and finite implication do not coincide. TFDs relate and extend some earlier work on dependency theory in temporal databases. Throughout this paper, the construct of TFD is compared with the notion of temporal FD introduced by Wang et al. (1997). A comparison with other related work is provided at the end of the article.