Structure models
Structure models test whether you can express composition, interconnection, interfaces and value properties with blocks. Expect questions on part versus reference properties, on block definition diagrams versus internal block diagrams, on ports, connectors and item flows, and on value types with units.
Blocks and properties
«block» is the unit of structure, a UML Class carrying the stereotype. A block owns properties, operations, ports, connectors and constraints, and can be generalized. A part property is composition: the part is owned, drawn with a filled diamond. A reference property points at an element owned elsewhere, drawn with a hollow diamond or a plain association. Multiplicity on a part (engine : Engine [2]) is a structural constraint, not a runtime count.
Definition versus usage
The Block Definition Diagram shows definitions: types, generalization and composition. The Internal Block Diagram shows one usage context: the parts inside a block, connected by connectors, with ports on the boundary.
Ports, connectors, item flows
A proxy port's features come from its type, typically an «interfaceBlock»; a full port owns its features; the older flow port is item-based with in, out or inout direction. Connectors link parts and ports inside an IBD, and an item flow on a connector states what travels, for example fuel : Fuel. Item flow types must be compatible with the ports at both ends.
Values and units
Value properties are typed by «valueType» or a UML data type. For engineering quantities, give the value type a dimension and a unit, and use the units library so results stay consistent.
Worked example
A UAV block owns engine : Engine [2]; each engine exposes proxy port fuelIn : FuelPort; a connector from the tank port to engine.fuelIn carries item flow fuel : Fuel. The BDD shows the composition; the IBD shows the two ports and the routing.
Traps
Drawing connectors on a BDD, confusing a part property with a reference property, omitting multiplicity, typing a port with a block instead of an interface block, adding an item flow to incompatible ports, and modeling a part as a value property.