We start our introduction to Ports with an Internal Block Diagram (IBD) with a single Port symbol on the boundary of the diagram frame, which frame represents the boundary of a Block between itself and its environment:

SysML-1.6: 'Ports are notated by rectangles overlapping the boundary of their owning blocks or properties (parts or ports) typed by the owning block.'

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At this stage, we are only looking at types of connections made directly to from a boundary Port to part properties of the owning Block (we'll see later that owned properties of a Block may also have Ports if they are typed by a Block that has Ports).

A Connector from a boundary Port to an inner Property - such as from p:DelegatingPort to b1:InnerBlock1 - is of kind delegation,

From the software-centric UML world:

UML-2.5.1: 'A delegation Connector is a Connector that links a Port to a role within the owning EncapsulatedClassifier. It represents the forwarding of requests (Operation invocations and Signals). A request that arrives at a Port that has a delegation Connector to one or more Properties or Ports on Properties will be passed on to those targets for handling.'

In SysML, the sense of delegation is far broader, and can involve data, information, material, energy (or anything else that can flow) or anything that can be provided or required.

A Connector from an inner Property to another inner Property - such as from b1:InnerBlock1 to b2:InnerBlock2 - is of kind assembly.

One of the nicest extensions of SysML over UML is the ability to connect across boundaries to inner Properties of Properties, such as from b1:InnerBlock1 to nb:NestedBlock across the boundary of b3:InnerBlock3:

SysML-1.6: 'Connectors may be drawn that cross the boundaries of nested properties to connect to properties within them. The connector is owned by the most immediate block that owns both ends of the connector.'

SysML has special a requirement for being allowed to connect across the boundary of a Property typed by a Block, the Block must not have 'isEncapsulated' true:

SysML-1.6: 'Block::isEncapsulated : Boolean [0..1] If true, then the block is treated as a black box; a part typed by this black box can only be connected via its ports or directly to its outer boundary.'

SysML-1.6: 'Block::isEncapsulated : Boolean [0..1] ... If false, or if a value is not present, then connections can be established to elements of its internal structure via deep-nested connector ends.'

Finally, note that the boundary Port has isBehavior false, which just means it does not delegate to the owning block itself:

UML-2.5.1: 'A Port has the ability, by setting the property isBehavior to true, to specify that any requests arriving at this Port are handled by the Behavior of the instance of the owning EncapsulatedClassifier, rather than being forwarded to any contained instances'

SysML has an additional special kind of connector called the BindingConnector we'll see later

Up next

NestedConnectorEnd: Connecting across the boundary of a part property

Notes

[GOTCHA, TIP]{INFORMATIVE} SysMLv1: A 'part property' in SysMLv1 does not formally include 'port' (which is considered a special kind of property), even though the Port metaclass in UML2 extends Property and a 'port' may have 'composite' aggregation and be typed by a Block.

Snippets (quotes/extracts)

[SysML-1.7] Connectors may be drawn that cross the boundaries of nested properties to connect to properties within them. The connector is owned by the most immediate block that owns both ends of the connector.

[SysML-1.6] Ports are notated by rectangles overlapping the boundary of their owning blocks or properties (parts or ports) typed by the owning block.