A model-based approach to updating databases with incomplete information

  • Authors:

  • Marianne Winslett

  • Affiliations:

  • Univ. of Illinois, Urbana

  • Venue:
  • ACM Transactions on Database Systems (TODS)
  • Year:
  • 1988

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Abstract

Suppose one wishes to construct, use, and maintain a database of facts about the real world, even though the state of that world is only partially known. In the artificial intelligence domain, this problem arises when an agent has a base set of beliefs that reflect partial knowledge about the world, and then tries to incorporate new, possibly contradictory knowledge into this set of beliefs. In the database domain, one facet of this situation is the well-known null values problem. We choose to represent such a database as a logical theory, and view the models of the theory as representing possible states of the world that are consistent with all known information.How can new information be incorporated into the database? For example, given the new information that “b or c is true,” how can one get rid of all outdated information about b and c, add the new information, and yet in the process not disturb any other information in the database? In current-day database management systems, the difficult and tedious burden of determining exactly what to add and remove from the database is placed on the user. The goal of our research was to relieve users of that burden, by equipping the database management system with update algorithms that can automatically determine what to add and remove from the database.Under our approach, new information about the state of the world is input to the database management system as a well-formed formula that the state of the world is now known to satisfy. We have constructed database update algorithms to interpret this update formula and incorporate the new information represented by the formula into the database without further assistance from the user. In this paper we show how to embed the incomplete database and the incoming information in the language of mathematical logic, explain the semantics of our update operators, and discuss the algorithms that implement these operators.