Message Exchange Patterns (MEPs)
<operation>specifies logical message exchange- MEP defines a pattern of interaction between agents
- sequence
- cardinality
- direction
- Base set of MEPs:
- In-Out, In-Only, Out-In, Out-Only
- Robust-In-Only, Robust-Out-Only (permit optional fault)
- Out-Optional-In, In-Optional-Out (reply is optional)
- Extensible: other MEPs can also be used (identified by URI)