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Block Definition Diagram

The Block Definition diagram is the most widely-used of the SysML diagrams; it is used to model Blocks, their relationships to other elements (including other Blocks) and their features in the form of Properties, Operations and Receptions. Blocks are modular units of system description and provide a way of modeling systems as a graph or tree of modular units. Other elements, such as ConstraintBlocks and Properties, can also appear on the diagram and help describe the system being modeled. For more information see the Block Definition Diagram Help topic.


The main elements that can appear in Block Definition diagrams are provided by the Diagram Toolbox for this diagram type:

The main connectors that can appear in Block Definition diagrams are as shown:


A variety of tools can be used with structural modeling and Block Definition diagrams, including:

  • Diagram Filters - which allows a user to filter elements out of the diagram to achieve a more specific focus,
  • Pan and Zoom - which allows a modeler or viewer to easily move around large diagrams,
  • Spreadsheet (CSV) Import and Export - which allows content in spreadsheets to be imported or exported from the model,
  • Documentation - which allows formal or informal documentation to be generated from the model in a variety of formats,
  • Traceability - which provides a hierarchical view of an element's relationships to other model elements,
  • Responsibilities Window - which provides a composite view of the important responsibilities of an element, including Constraints, Requirements and Scenarios
  • Relationship Matrix - which allows the connections between Blocks (or other elements) and other elements such as Requirements and Use Cases to be visualized in a matrix.


The Block Definition Diagram is a general-purpose diagram that can be used to describe the structural aspects of a system.