Ports and Terminals

This model shows ports and terminals in more detail. This model in particular clarifies the role of "multi-ports." I have used the composite attribute to flag a multi-port, as I didn't think there was sufficient difference to warrant making atomic and multi-ports into sibling classes.

Notes on the model:

• A MetaIcon has a set of TermStyles qualified by name; each contains a set of MetaTerms also qualified by name. The idea here is to allow the icon designer to choose and limit the ways in which ports can be displayed for an icon. (I wondered whether terminal style should be specified by the star rather than the icon, but decided that the icon designer gets to choose (and limit) the terminal styles of each icon.)

• In addition, a MetaIcon can also contain a set of terminals. This is mainly for convenience -- it is not compulsory to create a separate termstyle of none exists -- and gives the set of terminals that will be used if none is specified when the icon is created.

• MetaStar contains a set of MetaPorts, qualified by name. Each MetaPort has the datatype it carries, a flag indicating whether it is a composite port, and a flag indicating whether those ports are ordered. All of these are reflected in the Port instances.

• MetaPort and MetaTerm, and Port and Terminal, have one of two possible associations. Either
  1. The objects at either end of the association are both composite or both atomic. In this case, one port maps to exactly one terminal.
  2. The port end of the association is composite and the terminal end is atomic. In that case, each port maps to multiple terminals, qualified by the instance number. This reflects the situation where connections are made to individual ports within a multiport.

• There is a (necessary) difference between terminal name and port name. The terminal name will likely be formed by concatenating the port name and the instance number.

• Each Edge connects to up to two Ports. The connects association is qualified by the end (for want of a better name) at which it is connected. end can be either "source" or "target". The multiplicity at the Port end of the association is zero or one -- that is, the Edge may not be connected to a Port at all. This is used to support support editing of partially constructed graphs. Each connection between a Port and an Edge has an optional instance attribute -- this is present if the Port is composite.

• A Net graphically represents an Edge. Net's are connected to up to two terminals, one at each end.

JohnR, 14 Oct 97, updated 11/07/97