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Data Exchange and Schema Mappings in Open and Closed Worlds

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Le mardi 01 avril 2008 à 11:00
Salle de Conférence (Pavillon des Jardins)
Cristina Sirangelo (University of Edinburgh)

Data exchange is the problem of translating a source database structured according to a source schema into a new database structured according to a given target schema, known the relationship between the source and the target (schema mapping). Two semantics of data exchange and schema mappings have been proposed in the literature:

  • an open-world (OWA) semantics , which allows target instances to contain arbitrary extensions of the data translated from the source,
  • a closed-world (CWA) semantics, which only allows to exchange "as much data as needed" to satisfy the constraints of the schema mapping.
This work proposes a new mixed OWA/CWA semantics that generalizes and unifies the previous ones: it allows different target attributes to import data according to different semantics (either open-world or closed-world). This approach allows more flexibility in the specification of schema mappings and collapses in the known OWA and CWA approaches when target attributes are either all open or all closed. Under such mixed semantics, we address two of the main issues in data exchange and schema management: query answering and composition of schema mappings. In particular we study how their complexities depend on the number of open attributes and we identify new conditions under which schema mappings compose.

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