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Persistence descriptor 10 The persistence descriptor is used at enhancement time to identify classes to be made persistence-capable. Some of the information it contains may additionally be used by the implementation at runtime particularly vendor-specific enhancements such as data store mapping information. The persistence descriptor is an XML document. A brief overview follows for readers not yet familiar with XML. 10.1 XML overview Markup languages, which allow text data to be structured using a set of prescribed tags, have been in use for many years. XML is a particularly simple markup language. It defines neither the tags nor the grammar according to which the tags can be combined. Tag names for XML documents are defined by the document author in accordance with the information being marked up. This affords great flexibility. In a JDO persistence descriptor, the tags include ,
, and . Tags are not case sensitive. All XML documents must be well formed, in that each opening tag must be matched by a corresponding closing tag. Closing tags carry a preceding forward slash character, as in , , and . The sequence in which tags are closed must match the sequence in which they were opened. Pairs of opening and closing tags may have content between them. Often this content will include other tags as appropriate to the data being marked up. Additionally, tags may contain attributes. These are name value pairs occurring within the opening tag. An example is the name attribute of the tag: class tag content goes here A tag that is opened and then closed with no intervening content may be written as a single empty tag for convenience. Empty tags may still contain attributes and are notated with a trailing forward slash character, as in . Thus is equivalent to

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