While the Diagram Editor does not provide as extensive editing options for ports as it provides for most other metatypes, ports still remain an important diagram element type. The strength of ports is their ability to characterize how the roles are connected with objects in bindings, making them a prominent concept during the relationships and role creation when present.

Static ports are – as their name implies – defined as constant static parts in object symbols, so all instances of a given type have the same ports. For example, in Figure 4–16 below, both A and B have explicit rectangular areas that stand for the IN and OUT ports:

During relationship or role creation the ports are offered as connectable areas when the cursor is over them, as shown in Figure 4–17:

The connection is validated when the binding is completed. Ports, if present in the metamodel, add more precision to the binding semantics, enabling us to define such advanced binding rules like ‘connections from the OUT port must connect to the IN port at the other end’, as in our example above. The static ports also have properties that can be used to form even more precise rules. For example, if our OUT and IN ports have a property Voltage, we could say that the connection between them is possible only when the value for the Voltage property is the same for both ports (i.e. only 5V IN can be connected with 5V OUT). These rules are defined by the metamodeler, and the port property values are not directly visible to the modeler: the rule will be explained when the modeler tries to break it.

The main difference between static and dynamic ports is that while the former are always defined as constant part of the object’s symbol and refer to an existing Port instance, the latter are dynamically created references to other Objects in the model. Dynamic ports are fetched at runtime and they can come from various sources: they can be in the host object’s properties or objects from its subgraph, or they can be collected with a generator. Once fetched, the dynamic ports are shown as part of the object’s symbol, as in Figure 4–18.

Dynamic ports are revealed as connectables during relationship or role creation, in a similar way to static ports, and they provide similar ways to extend the binding semantics. There is, however, one difference between static and dynamic ports when they are connected: while static ports are always fixed to the location defined by the symbol, dynamic ports can be moved if the metamodel allows it. To move a dynamic port, select the role attached to it and drag the handle at the port end of the role.