Schema mappings declaratively specify the relationships between database schemas. They are widely used in systems and applications that require interactions of heterogeneous data, such as data exchange and data integration. In this dissertation, we investigate two problems of schema mappings, namely managing priorities of relationships between schemas in schema mappings, and deciding and describing the ability of mapping source instances to target instances for schema mappings.
S-t relationships (relationships between source schemas and target schemas) may have different priorities for user tasks: different parts of source data can be related by different s-t relationships to target data, and some s-t relationships are better than others. We would like to find a best way to relate source data to target data. The classical schema mappings, however, lack adequate concepts and semantics to capture such priorities. In the first part of this dissertation, we study managing priorities of s-t relationships in the context of schema mappings. We first introduce a language for modeling s-t relationships with priorities based on the language of classical schema mappings. The language enables capturing two aspects of the semantics of s-t relationships, namely which data must be included in the target instance and which data must be excluded from the target instance given a source instance. We then devise a framework of schema mappings with priorities, which aims at finding a best way to relate source data to target data based on priorities of s-t relationships. We also present algorithms for computational problems in query answering of schema mappings with priorities. To name some example areas of application, schema mappings with priorities enable accommodating exceptions to s-t relationships, provide a formal way to model user preferences and comparative values between s-t relationships, and enable detecting target data that are no longer "favored" in the light of new source data.
In the second part of this dissertation, we study schema mapping coverage. Given a schema mapping in the presence of both source dependencies and target dependencies, the schema mapping coverage problem is to decide and describe which source instances have solutions under the mapping. Our main motivation is to describe limitations of schema mappings and hence to effectively determine if they can fulfill user expectations for the given tasks. We first propose using database dependencies to model user expectations of schema mappings. Then we formally define the notion of schema mapping coverage and propose a characterization of coverage. To compute schema mapping coverage, we look into how target dependencies indirectly enforce dependencies via mapping specifications on source instances and thus determine which source instances have solutions. We present algorithms for computing coverage for schema mappings in which both the source dependencies and the target dependencies consist of functional dependencies and acyclic inclusion dependencies. Schema mapping coverage is especially useful for schema mapping design and evolution as it describes limitations of mappings and enables comparing different mappings.
|Commitee:||Jayaraman, Bharat, Kennedy, Oliver|
|School:||State University of New York at Buffalo|
|Department:||Computer Science and Engineering|
|School Location:||United States -- New York|
|Source:||DAI-B 81/8(E), Dissertation Abstracts International|
|Keywords:||Databases, Priorities, Schema mappings|
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