Can One Escape Red Chains? Regular Path Queries Determinacy is Undecidable
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For a given set of queries (which are expressions in some query language) Q={Q_1, Q_2, ... Q_k} and for another query Q_0 we say that Q determines Q_0 if -- informally speaking -- for every database D, the information contained in the views Q( D) is sufficient to compute Q_0( D). Query Determinacy Problem is the problem of deciding, for given Q and Q_0, whether Q determines Q_0. Many versions of this problem, for different query languages, were studied in database theory. In this paper we solve a problem stated in [CGLV02] and show that Query Determinacy Problem is undecidable for the Regular Path Queries -- the paradigmatic query language of graph databases.
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