BPMN21 — Rethink implementation attribute in Send/Receive/Service Tasks

Currently, send/receive/service/user/business rule tasks have an "implementation" attribute. Based on the information in the spec and from the process orchestration subgroup call, this attribute shall identify the technology to be used for interaction. This can be Web Service, WS-HT or any other protocol/coordination protocol.

While this makes sense for human tasks and business rule tasks, there are a couple of inconsistencies with Send/Receive/Service tasks. Here is why:

• Receive Task has an implementation attribute, a message event has not.
• A Receive Task and a subsequent Send Task that deal with messages defined within the same operation may have different values for the implementation attribute. This is however probably not intended.

My proposed resolution is to remove the implementation attributes for send/receive/service tasks. We should discuss whether this information is really needed or whether it could be inferred by the implementationRef of the interface/operation tuple. The information might be needed to determine in which technology an interface/operation is implemented. See also http://www.osoa.org/jira/browse/BPMNFTF-519#action_15739

As an alternative, MessageEventDefinition would need such an attribute as well.