MessageBrokerService

A MessageBrokerService is a service distributing messages to other services and pooling their responses. It has a single AccessPoint. A MessageBroker will be used for portals but can also be used in a cascading way to create local networks, e. g. for special interest groups. In this way it serves as a gateway to a complete network of distributed services with (potentially) its own registry of services.

Making the protocol compliant with MessageBrokers would not be a trivial task, and probably other more generic protocols would better support query distribution. Such protocols could already exist, but we have not investigated with more details.

Therefore we do not specify a complete protocol for brokers now, but we think they are the generalized form of a ProviderService for which a protocol is being specified.

Suggestions for a Broker Service Protocol

Based on the ProviderService protocol there are some additional complications:

• Brokers can be cascading, therefore ...
• how to adress destinations in the header? Do we need to be able to pass on a message to only a subset of other services somewhere down the line/tree of services?
• how to avoid vicious circles MessageBrokerService loops in the forwarding of messages?

Current Protocols

Although the DiGIR? protocol has some elements especifically related to that service (e.g. "responseWrapper" element and multiple destinations), it is not validating all messages exchanged between clients and the "portal" engine, and it seems the protocol is not officialy supposed to cover these types of messages. BioCASE? on its turn uses a java API for that purpose.