This is a Block Definition Diagram (bdd). It is commonly used to model structures.

Structures (i.e. a BOM) are modeled with Part Association (sometimes referred to as Composite Association) edges. These edges relate a Whole with a Part.

Note that the default multiplicity on the Whole end is [0…1]. The [0] means that if the Whole did not exist then the Part would still exist. If the multiplicity was [1] (it can not be higher than 1) then if the Whole did not exist the Part would also not exist.

Note that sometimes it is convenient to provide alternative hierarchies for systems. E.g. Electrical structure. In this case use Shared Association edge.

This is an Internal Block Diagram (ibd). It is commonly used to model interfaces between parts.

In the below diagram there are two usages of Block3 (b3_a and b3_b) in the context of Block1, each with a multiplicity of [1]. However the definition of Block3 also includes a part defined by Block5. How many usages of Block5 exist?

The answer is two. b3_a and b3_b each include a part defined by Block5.

In the case of Block2 it has a multiplicity of [2] in the context of Block1. This means that there are two Block2 parts in the Block1 whole. How many usages of Block4 exist?

The answer is also two. Even though the individual usages of Block2 have not been assigned a part name in each usage there exists one part defined by Block4.

The modeling program automatically assigns the {unique} property to Block2 if the upper limit multiplicity is greater than [1]

The resultant internal block diagram looks like this. Note that if the usage of Block5 was given a name the same name would appear within the two Block3 parts.

Ordered states that the parts (if multiplicity > 1) are in a certain order, typically in a natural number order: 1, 2, 3 etc. To establish this property in the Connector Properties → Source set Ordered to TRUE (by default it is FALSE). The {ordered} notation appears below the multiplicity adjacent to the composite edge.

Unique states that within the set there are no parts that are the same. As mentioned this is automatically assigned to the part property in the whole block if the multiplicity > 1. To override this, in the Connector Properties → Source set Allow Duplicates to TRUE.

Namespace treats the package hierarchy analogous to a folder directory except the '/' (or '\' in Windows) is replaced with '::'. However semantics is simpler. In the below example Block1 and Block21 share a 'root' package '7-1-2_namespace' but are in different levels.

If Block21 were to be linked in the same package as Block1 then the block's name is qualified with the namespace resulting in a full name, Package21::Block21

Property foo is typed by block PropertyDef. It appears as foo:PropertyDef. Block2 includes property foo2:PropertyDef and Block3 includes property foo3:PropertyDef.

Both Block2 and Block3 are parts of Block1

In the figure below, on the left, is the ibd of Block1 with properties nested in the parts. On the right is the ibd with the parts' properties shown without being nested in the parts.

Association blocks are used to type connectors. To use:

In the block definition diagram toolbox choose 'Association Block' Draw the relationship between the blocks you want to type an association block. Note that by default direction is not specified. Name the new block (in this example 'Power Cable')

Draw a composition relationship between Power Cable block to the whole block ('Logical Rover') Select the association relationship. Give it a name ('PwrCable')

In the internal block diagram draw a connector between the two part properties you want to connect Right click connector → Advanced → Set Connector Type… Choose the PwrCable association You've successfully type an association!

You may want to create reference systems to organize the part structure in different ways. For example you may only be interested in the power sub system of the system, or the control sub system. In a typical BOM hierarchy parts are segregated by the physical location of parts which may defy a pan-system sub system such as power.

Assuming that you create a BOM like structure already you do the following In a new BDD create a Block 'Power Sub-system' Drag in existing Blocks that you want to include in this sub system. In the below example I have Power Source and Camera. Use the 'Shared Association' relationship to connect Power Source to Power Sub-system. To create the relationship you start the drag from Power Source (source) to Power Sub-system (target). Notice that the blank diamond is at the Power Sub-system end. Note: Don't use the 'Reference Association' as the created relationship is weak and will not be useful in the following steps.

Now create a IBD with the Power Sub-system being the frame. In the element tree drag the reference properties ': Camera' and ': Power Source' in to the IBD. You will notice that these properties have a dashed boundary which explicitly state that these properties are reference properties. Add a connector between the properties if there is necessary (assuming that there is actually a connector). Done