UCM11 — Improve component port declaration

Component ports in UCM are specified by 3 parameters:

• a name
• a définition
• bindings to actual types if need be

UCM defines a set of nested classes in the meta-model, which makes the XML syntax verbose. See for example:

<compType name="Compare">
  <port name="in1">
    <typeSpec type="::core::messages::msg_rcvr_pt">
      <binding abstract="::core::messages::api::message_type_t" actual="::complex_types::image_t"/>
    </typeSpec>
  </port>
  <port name="in2">
    <typeSpec type="::core::messages::msg_rcvr_pt">
      <binding abstract="::core::messages::api::message_type_t" actual="::complex_types::image_t"/>
    </typeSpec>
  </port>
</compType>

Three nested XML tags are necessary: port, typeSpec and binding.

The specification of data binding is nested in the port declaration. Although it is a clean way to specify bindings, it brings two issues:

• users have to write the binding specification for each port; a binding cannot be written once and used for several ports, which would be simpler
• it is difficult to implement efficient code generators: a naive generator will generate specific code for each port instead of for each unique binding; this leads to redundant code.

It would be better to write something like this:

<bindingSet name="binding1">
  <binding abstract="::core::messages::api::message_type_t" actual="::complex_types::image_t"/>
</bindingSet>

<compType name="Compare">
  <port name="in1" def="::core::messages::msg_rcvr_pt" binding="binding1"/>
  <port name="in2" def="::core::messages::msg_rcvr_pt" binding="binding1"/></compType>

Also, when refining a component type, ports can be refined. By “refined”, one must understand “redefined”: UCM actually allows a complete port redefinition; no shared data or semantics is required between the original port and its refinement.

Improve component port declaration

introduce the notion of PortRole to restrict component port refinement: a component port can only be refined by a component port the port type of which references the same port role. For example, a message emitter port can refine a data producer port, but not a service client port.
Also remove the notion of IPortSpec, PortTypeSpec and PortRoleSpec, and instead have a reference to the port type and binding in the port declaration.