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Views for XML
A mechanism for defining and querying views on native XML data.
Date Posted: March 18, 2004
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What is Views for XML?
Views for XML is a mechanism for defining and querying views on native XML data. It is designed for XML users and JavaTM developers working with applications that deal with data stored in XML format. It provides mechanisms for defining views relevant to the application. The application developer can then have the view itself as a data abstraction and not be bothered about the remaining data in the repository (which is irrelevant to the application being developed). Thus it simplifies application development.
This facility could also be used to provide security, since a user of a view can be denied access to other parts of the data repository. Views for XML provides facilities for defining fully-composable views (that is, views can be defined on views), and also provides mechanisms for mapping user queries against the view to the actual physical XML files in the data repository.
How does it work? The users are first allowed to define views on native XML repositories using XQuery. Any XQuery expression written for the XML repository can be considered as a view definition query. The tool analyzes the definition query and computes the XML schema for the view with the information available (this entails static type analysis). This view schema is presented to the user.
The user then writes XQuery expressions against the view schema, and the tool automatically maps the user query against the view into a query against the actual physical schema. This query can then be executed by the user to get the information requested in the query. Note that the views are not just portions of data, but are composed using the full power of XQuery, and hence can consist of any information generated by the XQuery expression.
The system works by maintaining information about the view query in suitable data structures. When the user query arrives, efficient query rewriting is done to map the query to the actual schema. This functionality is provided to the users in the form of a Java API that can be used in their applications. Also shipped with the package is a sample user interface that can be used to define and test views directly in XQuery (without Java).
Further information is available in this white paper.
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| | About the technology author(s):
This technology has been developed by Deepak Srinivasa and Rajeshwari Rajendra.
Deepak M. Srinivasa is a staff software engineer at the Technology Incubation Center, IBM Software Labs, India. His interests include XML and Computational Biology. He is also the inventor for about eight patent applications that IBM has filed. Mr. Srinivasa can be reached here.
Rajeshwari Rajendra is a software engineer at the Technology Incubation Center, IBM Software Labs, India. Her interests include XML and compiler techniques. She can be reached here.
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