4.2.11 Connections

Before connections can be established, servers that passively wait for incoming connection requests must be located. The name patterns or types of those servers are specified under the COMPONENT descriptor. Like the PORT descriptor, each COMPONENT descriptor is followed by the properties of a component or a group of components that matches a certain criteria:

• The id property defines a GUID for the component (or group of component). Each group of components that matches a name pattern must be assigned a unique GUID.

• The name property, unlike the name of a port, specifies a name pattern for the group of components. The format of the name pattern follows the conventions of UNIX regular expressions. All the components with a name matching that pattern are selected as members of the group. Hence, a message sending to a group of components will be broadcast to all its members.

  For example, names ``model1'', ``model'' and `` model123'' match name pattern ``model[0-9]*''.

• The type property specifies the type of a group of components. It is a string that lists the in-ports, out-ports and inout-ports. An in-port is listed as in; an out-port is listed as out; and an inout-port is listed as inout. Multiple ports are separated by one or more spaces. An integer number can be added before a type to specify multiple ports of the same type. For example, ``type = in in out inout inout'' matches components with 2 in-ports, 1 out-port, and 2 inout-ports. ``type = 2 in out 1 inout 1 inout'' has exactly the same effect.

The name property or the type property or both must be specified for each group.

Connections are established between ports and the ports of the servers under the CONNECTIONS descriptor. One or more links can be defined. The left-hand side of a link is connected with the right-hand side with double hyphens (``--''). Suppose the ID of a component group is C and the model wants to connect to port p of the group with its port q, the link should be written as either ``q -- C.p'' or ``C.p -- q''.

Table 4.12: An example of the textual representation of connections

As an example, suppose a server is given ID ``Server0'' and it has inout-port p, in-port q and out-port r, the model in Figure 4.14 is written as Table 4.12.