Reasoning about participation constraints and Chen's constraints

  • Authors:

  • Sven Hartmann

  • Affiliations:

  • Information Science Research Centre, Massey University, Palmerston North, New Zealand

  • Venue:
  • ADC '03 Proceedings of the 14th Australasian database conference - Volume 17
  • Year:
  • 2003

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Abstract

Cardinality constraints are often considered as one of the basic constituents of the entity-relationship approach to database design. In his original proposal of this model, Chen [6] defined cardinality constraints as look-across constraints. Alternatively, however, cardinality constraints may also be defined on the basis of the participation or look-here interpretation.While both definitions correspond to each other for binary relationships, they differ for n-ary relationships (with n ≥ 3). Participation constraints restrict the number of relationships a fixed object may participate in. Chen-style constraints limit the number of objects that co-occur with a given tuple comprising instances of the remaining n - 1 components of the relationship type under discussion.In our paper we present a sound and complete system of inference rules for a class of generalized cardinality constraints containing both, participation constraints and Chen-style constraints. It turns out that both constraint classes are almost independent, which justifies their juxtaposition in conceptual database design. Similar results will be presented in the presence of additional functional dependencies. The paper concludes with an axiomatization for the joint class of generalized cardinality constraints and functional dependencies.