There can be distinguished two families of Petals components.

*Binding components (BC)* are links between the services in the bus and external applications.
The natural way to provide these bounds is the usage of communications protocols. This is why binding components are generally associated with communication protocols, like SOAP, RMI, JMS...

*Service engines (SE)* are pieces of application logics fully integrated in the bus.
They are exposed directly as services into the bus. It can be executing code (POJO), performing transformations (XSLT), scheduling (Quartz) and so on...