These diagrams show the physical structure of some or all of a system at a particular level. The PAD shows the physical flows between the system components at the level of interest.
Every symbol in the diagram represents something physical, including paths through which data passes. Therefore, a data link on a PAD corresponds to a physical interface connection, i.e., cable, bus, and so on.
It will be common to have both an AID and a collection of PADs in an architecture model. The AID will show the physical components and the logical connections between them. There will be one or more associated PADs, each showing the same physical components, but showing alternative physical connections (such as a bus or point-to-point links) by which these components are interconnected in that specific topology). PADs are hierarchical. Their connectivity is:
PADs can only appear in models in the Implementation Domain.
An equipment can have any number of ports.
Within PADs there are two ports:
Each port is identified by a name that must be unique for an equipment.
Public ports are the externally-visible side of an interface and must be embedded within the equipment to which they refer, e.g.:
The above example shows that:
Internal ports are the internally-visible side of an interface and cannot be embedded in an equipment. They (one or more of them) are the external links from the top-level PAD inside an equipment:
The link between the public port symbol and the internal port symbol(s) is made solely by the port name.
The example above shows that equipment Equip A:
Repeating the idea in Equip B, an example could be:
The example above shows that:
Sends data xx and yy to port MainReceives aa and bb from port Main
Sends data uu, vv and ww to port AuxReceives mm, nn and oo from port Aux
The input to the Main port of Equip A, that is: aa and bbThe output from the Aux port of Equip B, that is: uu, vv and ww
The output from the Main port of Equip A, that is: xx and yyThe input to the Aux port of Equip B, that is: mm, nn and oo
This shows that ports:
With its source interfaceWith its destination interface
Ports are important for consistency checking. Public ports (on a higher level diagram) match internal ports (on a lower level diagram) provided that they have the same name. For a pair of such matching ports, the Consistency Checker will apply full flow balancing between the I/Os to such ports. Each such balancing applies individually and separately between each pair of matching ports. All such port-related balancing is separate from, and in addition to, the normal inter-diagram I/O balancing checks.
The numbering system for PADs is alphanumeric dot-decimal.
The start of each architecture is a top-level PAD that is typically given a number to represent that architecture. The hierarchy of diagrams and specifications created below it will follow this number with a dot-decimal suffix.
An example PAD is:
The symbols available in PADs are: