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Java Cookbook
book

Java Cookbook

by Ian F. Darwin
June 2001
Intermediate to advanced content levelIntermediate to advanced
888 pages
21h 1m
English
O'Reilly Media, Inc.
Content preview from Java Cookbook

Verifying Structure with a DTD

Problem

Up to now, I have simply provided XML and asserted that it is valid. Now you want to verify the structure using a Document Type Definition (DTD).

Solution

Write the DTD and refer to it in one or more XML documents.

Discussion

This is not the place for a full dissertation on creating a Document Type Definition. Briefly, a DTD consists of a header and a list of the elements and any attributes. The DTD is written in a special language that allows you to specify the elements and attributes. Example 21-7 is people.dtd , a DTD for the people.xml file used earlier in this chapter.

Example 21-7. people.dtd

<!ELEMENT people (person)*>
<!ELEMENT person (name, email, country)>

<!ELEMENT name (#PCDATA)>
<!ATTLIST email type CDATA #IMPLIED>
<!ELEMENT email (#PCDATA)>
<!ELEMENT country (#PCDATA)>

To verify that a file conforms to a DTD, you do two things:

  1. Refer to the DTD from within the XML file, as is sometimes seen in HTML documents. The <!DOCTYPE> line should follow the <?xml> line but precede any actual data.

    <?xml version="1.0"?>
    <!DOCTYPE people SYSTEM "people.dtd">
    
    <people>
    <person>
    <name>Ian Darwin</name>
    <email>ian@darwinsys.com</email>
    <country>Canada</country>
    </person>
  2. Pass true as a second argument to the createXMLDocument( ) method; true means “enforce document validity.”

    XmlDocument doc = XmlDocument.createXmlDocument(uri);

Now any elements found in the document that are not valid according to the DTD will result in an exception being thrown.

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Publisher Resources

ISBN: 0596001703Supplemental ContentCatalog PageErrata