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One of the reasons we needed to learn SQL is because information that is stored in a database has a complex structure. SQL provides a language that allows us to extract information from complex structures in a logical and predictable way. The other main reason was that databases tend to be large and we often only need to extract a subset of the data.
Data sets that are stored as XML also tend to be large and can have a complex structure, so there is a need for a language to express subsets of XML documents. That language is XQuery.
A full discussion of XQuery is beyond the scope of this book, plus it is harder to find software that implements the language (compared to SQL).
Paul Murrell
This document is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.