Composite Materials

The Role of Metadata in JBI

Metadata plays an important role in JBI. Metadata has two major uses:

• Service description. A service describes itself, using WSDL 2.0.
• Message description. Extra information about a normalized message.

Services are described using WSDL. The description includes the basic stuff of how the service is invoked (message exchanges), but can also include more esoteric data. JBI's so-called normalized message includes a message context that is a container for more (you guessed it) metadata. This includes simple things (like the address of the requester), and more interesting things, like security information and even transaction identifiers.

Both types of metadata are extensible, meaning that the JBI spec doesn't have to spell out every detail for every possible use case. Plug-in components are free to extend the basic metadata in ways that may not be understood by all other components, but which provides for extended interoperability between those components.

For example, an ebXML binding component and an ebXML BPSS service engine may use extensions to the normalized message context data to communicate ebXML-specific information, such as Service/Action names and CPA identifiers. If you don't grok ebXML, the basic point is: there are technologies needed in the integration world (and the SOA universe in general) that must share specialized, technology-specific metadata in JBI's message-passing model. JBI cannot specify all the technologies that possibly can be used in an integration solution based on JBI, and thus must allow for the unknown. Extensible metadata is the ticket to controllable, flexible extensions to the messages (and services) in JBI.

Posted at 06:56PM Jun 15, 2004 by rtenhove in Java Business Integration  |