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A query language for semi-structured data allows a user to extract items from a semi-structured data instance, or to transform it into another semi-structured data instance. The first type of expressions are called queries, the latter kind of expressions are interchangeably called queries or transformations. Query languages can be classified along several dimensions:
- 1.
Expressive power. What kind of queries or transformations can they express?
- 2.
Querying vs. restructuring. Some query languages allow only the extraction of items from the data, others allow the data to be transformed.
- 3.
Compositionality.Can the output of a query be used as input in another query expressed in the language, and is the composed transformation still expressible in the same language? Query languages that are restricted to extraction only are not compositional, because the type of their outputs are not semi-structured data instances. Transformation...
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Recommended Reading
Abiteboul S, Quass D, McHugh J, Widom J, Wiener J. The Lorel query language for semistructured data. 1996. http://www-db.stanford.edu/lore/.
Buneman P, Davidson S, Suciu D. Programming constructs for unstructured data. In: Proceedings of the workshop on database programming languages. 1995.
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Papakonstantinou Y, Abiteboul S, Garcia-Molina H. Object fusion in mediator systems. In: Proceedings of the 22th international conference on very large data bases. 1996. p. 413–24.
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Suciu, D. (2016). Semi-Structured Query Languages. In: Liu, L., Özsu, M. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4899-7993-3_339-2
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DOI: https://doi.org/10.1007/978-1-4899-7993-3_339-2
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