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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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There are many reasons for needing Views for XML. First, a number of applications have already been developed and are being developed using XML format as a data storage format. With the rapid growth of XML, one would quickly see the need for providing database-like facilities for XML, one of which is a view mechanism. The concept of views itself comes with a number of benefits:
- Views simplify application development by allowing application developers to define relevant portions of the database and to provide a level of abstraction.
- They are useful for simplifying frequently-used query types.
- They can help maintain confidentiality by restricting user access to selected parts of the database.
Views for XML can be used to realize some or all of the above benefits.
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This distribution of Views for XML comes with the following:
- Java class API -- the class library (viewsForXml.jar) by which a programmer makes use of Views for XML
- GUI Application -- an easy-to-use GUI (GUI.bat) for quickly seeing the application of the tool's API
- API documentation in the API directory
- Samples of XML Schema, input, and output in the Examples directory
- A Readme.txt file for installation and usage directions.
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An instance of the ViewDefinition class represents a Virtual View on the native XML data repository. It holds information about the view, such as the name, creator, date and time of creation, the XQuery query expression defining the view, and the XML Schema definition of the view structure. Read the API documentation for more information.
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ViewsManager is a singleton class used to manage the views on the XML data repository. It provides an API for creating, deleting, and getting information about a view in the system. It also maps user query-referring views to a query on base XML data files by the method of composition. Read the API documentation for more information.
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Yes! You can go ahead by using the sample GUI application provided with this distribution of Views for XML package. Running the GUI is as simple as executing the GUI.bat file in the root directory.
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This version of Views for XML does not support a mechanism for specifying access rights for users on defined views. It is a planned feature for a future release.
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To facilitate the view mechanism, the XQuery grammar has been extended with a built-in function called view (). This function takes in a constant string parameter that specifies the view name. It is similar in function to the document () function defined by W3C XQuery group, except for the fact that it provides access to virtual XML documents -- that is, the views. For help in using this function, please refer to the example XQuery expressions provided in the examples folder.
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Views for XML provides only a mapped query for a given user query and does not execute the same. Application developers are requested to use any of the available XQuery engines to execute the mapped query.
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One can easily learn to use the API by going through the included API documentation. The two important classes required for using the API are ViewsManager.class and ViewDefinition.class. Please see the questions above to learn more about these classes.
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The GUI helps you quickly see Views for XML at work. You can run the GUI application by simply executing the GUI.bat file. Alternatively, you can execute the com.ibm.tic.xml.xview.console.ViewsManagerConsole Java class by including the XML4J parser API (xercesImpl.jar and xmlparserapis.jar) along with Views4XML.jar in the class path. The GUI is intuitive and easy to use.
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Any queries or feedback can be directed to the following email addresses:
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