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    Observational Distinguishability of Databases with Object Identity

    Database Programming Languages

    Italy. 6th - 8th September 1995


    A.S. Kosky


    We will examine the problem of distinguishing between database instances and values in models which incorporate object-identities and recursive data-structures.

    We will show that the notion of observational distinguishability is intricately linked to the languages available for querying a database.

    In particular we will show that, given a simple query language incorporating a test for equality of object-identities, database instances are indistinguishable if they are isomorphic, and that, in a language without any operators on object-identities, database instances are indistinguishable if a bisimilarity relation holds between them.

    Further, such a bisimulation relation may be computed on values, but doing so requires the ability to recurse over all the object-identities in an instance.

    We will then show that systems of keys give rise to observational distinguishability relations which lie between these two extremes.

    We show that a system of keys satisfying certain restrictions provides us with an efficient means of comparing values, while avoiding the need to compare object identities directly.


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