Messages 

The Exchange Infrastructure message format is based on XML.Therefore, this documentation will refer to XML messages or simply messages.

Characteristics of XMeL

XML (eXtensible Markup Language) enables you to describe data in a highly intelligible form. An XML Schema Definition specifies which elements can be used, which attributes these elements have, and how they are structured. More than one Instance (a document that matches a XML schema definition) can exist for each schema. The following example of an instance illustrates that the elements in a schema are ordered hierarchically:

<PurchaseOrder no="1811">
  <ShipToParty>
    <Name>Rodney Washington</Name>
    <Address>200 S Wacker Drive Chicago IL 60606</Address>
  </ShipToParty>
  <Item> Bass Guitar No.14 </Item>
  <Status>Confirmed</Status>
</PurchaseOrder>

These elements (for example, <Item>) are also known as Tags in HTML.

You can describe the structure of a schema using an XML Schema. As well as the description of how the structure of an XML document looks (elements, attributes, hierarchy), this language allows you to define simple and complex data types. The following difference is important:

·        XML Schema Language provides a series of language constructs that you can use to describe an XML schema.

·        XML Schema Definition describes exactly one XML schema and is described using the XML Schema language.

·        More than one schema instance can exist for an XML schema. A schema instance is an XML document; its structure and values are defined using a corresponding XML schema definition. The process whereby the system checks whether an XML document matches a schema definition is called Validation.

You often also refer to an XML instance or schema instance instead of an XML document. The term XML document is normally used to refer to a document on a file system while the storage medium in the other two terms is less prominent.

There is a W3C recommendation dated May 2, 2001 for an XML schema that comprises three parts: XML Schema Part 0: Primer, XML Schema Part 1: Structures and XML Schema Part 2: Data Types.

Message Structure

A message in the Exchange Infrastructure is structured as follows:

The properties of the current message are contained in the message header (for example, the sender that will be used later to determine the receiver); the actual business data is transferred in the Payload (similar to <PurchaseOrder> used in the example above). You can also append an unlimited number of attachments to the message before it is sent. Attachments typically comprise non-XML data, for example, pictures, text documents and binary data.

Exchange Infrastructure messages are based on the W3C note SOAP Messages with Attachments (http://www.w3.org/TR/SOAP-attachments). Technically speaking, the message is sent as a MIME multipart document.

Using an XML schema you can describe any number of XML schema definitions for the payload of a message. The instance of a schema that is described using an XML schema definition is sent using the Exchange Infrastructure at runtime. The name of XML schema definition used is contained in the message header.