What is Block Definition Diagram?

The description of building blocks of a system

The block definition diagram – sometimes referred to simply as the block diagram – is a graphical representation of a system that describes functions and connections between individual components. Block definition diagrams take their name from the rectangularly drawn diagram elements used to describe hardware or software systems, processes, and procedures. The block definition diagram is considered one of the most important diagrams in the Systems Modeling Language (SysML), which originates in the Unified Modeling Language (UML). During the development of SysML, the class diagram of UML became the block definition diagram of SysML.

Elements in the Block Definition Diagram or Block Diagram

The following elements are used in block diagrams or block definition diagrams:

• Block: A system module for describing the logical and physical system components.
• Part: All parts connected to the block by composition.
• Reference: All parts modeled by association, aggregation or generalisation.
• Standard-Port: An interaction point of a system module with its environment.
• Flow-Port: An interaction point through which objects can flow into or out of the system module.

Relationships in the Block Definition Diagram aka Block Diagram

In a block definition diagram, there can be following relationships between different blocks against each other:

• association
• aggregation
• composition
• generalisation (where a block implicitly has all the characteristics of a general block)

Block diagrams are a widespread form of block definition diagrams. They are used in electronics to represent systems and circuits. Another SysML diagram can be used to display the internal structure of a single block: the internal block diagram.

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