Rational Developer for System z

XML wire format

The XML wire format is the physical representation of a message that can be parsed as XML.

Recall that a physical representation is just a set of assertions about how particular types of data in a message are represented when the data is stored in memory or on a hard disk. For example: which CCSID (character encoding) is used; whether the byte order is big endian or little endian; what format is used for floating point; what values are used for Boolean true and false; which day is the first day of the week; and so on).

The XML wire format is an instance of -- a real-life example of -- a physical representation, in which certain choices have been made as to the particular CCSID, the endian order, the floating point format, the boolean representation, and so on.

The term wire format is just a general term meaning a format for representing data in memory or on a hard disk. The word wire actually refers to the fact that this stored data is eventually sent out on a communications line ("sent out over the wire").

An XML wire format describes the physical representation of a message that is written according to the standards given in the W3C specification. The wire format defines information that is used to parse or write XML messages in a runtime environment.

You can add more than one XML physical format to a message set, but within that message set, each physical format must have a unique name. The default name for an XML wire format is XML1. Typically, you might do this if a single logical message can be represented with its components rendered in different ways, for example as the value of an element in one case but as the value of an attribute in another. The physical format name identifies the definitions that are to be used at run time.

After adding an XML physical format, all XML properties for all existing objects in the message set will be set to default values. Thus, immediately after adding the format and deploying the message set to a runtime environment, it is possible to process XML messages using MRM features.

You can configure XML properties for the message set, and for objects within the message set. Objects that can have XML properties are messages, elements, and attributes. For example, a message object can be customized to define a specific DTD declaration on output; an element can have a tag name assigned to it which is different from its MRM element name.

Adding an XML wire format to a message set allows you to both process input messages, and to construct output messages in this format. You can also transform messages between XML and either CWF or TDS.

XML messages are, by their nature, self-describing: each piece of data is prefixed by a tag name or an attribute name. Therefore, it is possible for an XML message instance to contain elements which are not in the MRM definition for that message.
  • If such an element exists in the message set, the MRM objects for that element are used in parsing or writing the message.
  • If the element does not exist in the message set, it is treated as a self-defining element and its data type is set to string.

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