Glossary · Systems engineering and MBSE
Block definition diagram (BDD)
German: Blockdefinitionsdiagramm (BDD)
In SysML, a block definition diagram (BDD) is a structure diagram that defines blocks and their relationships, such as composition, generalization and association, together with their properties, ports and operations.
- Systems engineering
In one sentence
A SysML block definition diagram (BDD) defines blocks, their properties and relationships such as composition and generalization.
Example
A BDD shows that the 'Palletizer' block is composed of a 'Robot', a 'Gripper', a 'Safety fence' and a 'Control cabinet', each with its key properties.
How it applies
- Engineering: BDDs define the system's building blocks and product structure; they are the basis for Internal block diagram (IBD)s and for allocation of requirements.
- Variant management: Generalization in a BDD can model product families (a base block with variants), which helps keep documentation variants aligned.
- Documentation: The block hierarchy is a good starting point for the component structure of a manual or an iiRDS product metadata taxonomy; the documentation team should align naming with the model.
- Model quality: Agree on modeling guidelines (naming, units, when to use composition or association) so different engineers produce consistent BDDs that tools and reviewers can interpret.
BDD vs. IBD
A BDD defines what types of blocks exist and how they relate in general. An IBD shows how the parts of one block are connected in a specific context.