Ports & interfaces

Structure isn’t only about what the parts are — it’s about how they connect. Ports, connectors, and interfaces describe the connections between parts, which is the heart of an internal block diagram.

Ports

A port is a defined connection point on a block — the place through which it interacts with the outside. SysML distinguishes a few kinds:

• Proxy port — exposes features of the block (or its internals) without adding behavior of its own
• Full port — a part of the block in its own right, with its own behavior and properties
• Flow port — focused on what flows in or out, such as a signal, energy, or material

Defining ports makes a block’s boundary explicit, so connections are deliberate rather than incidental.

Connectors

A connector joins two ports (or parts), expressing that they’re linked. On an internal block diagram, connectors are how you wire a block’s parts together to show how it works internally. Because connectors are model relationships, they stay consistent wherever the connected elements appear.

Item flows

An item flow records what travels across a connection — the data, signal, energy, or material that moves from one part to another. Item flows turn a bare connection into a meaningful statement about how the system operates, which matters when you reason about behavior, safety, or failure.

Interfaces

An interface defines the contract at a connection — what one side provides and what the other requires. Modeling interfaces explicitly lets you check that connected parts are compatible and gives you a clear specification of the boundaries between subsystems, which is exactly what integration and supplier hand-offs depend on.