Structure Block Definition Diagram (BDD) (available in CORE Spectrum)

The structure BDD represents the composition structure of systems, components, items, conceptual entities, and logical abstractions. Part of the physical architecture representation set, this is similar to a traditional physical hierarchy with select semantic and representational differences. Most notably, the structure block definition diagram can optionally indicate the role that the part plays in its parent and the multiplicity on the composition relationship (captured using the partMultiplicity attribute on the built from relationship).

The structure BDD is available for elements in the Component class (as well as any other subclasses of ImplementationUnit).

The structure BDD uses a structured layout with specific movement rules for each node. However, multiple vertical and horizontal layouts are available, so select the one that best fits your specific style and the specific data set.

CORE implements a second variant of the block definition diagram - a classification BDD  - to represent the inheritance tree for an implementation unit.

Multiple node representations are supported by block diagrams. In addition to the element name, you will frequently see some combination of the following fields:

• Operations - behavioral aspects allocated to the block. Operations describe synchronous interactions where the requester waits for the request to be handled. Operations reflect a subset of the allocated functions (both by definition and by the fact that users classically represent only a subset of operations on the node). This has been captured as the operations attribute. Note that for consistency, any operation listed here should also be reflected in the collection of functions allocated to this component.
• Receptions - behavioral aspects allocated to the block. Receptions describe asynchronous behaviors where the requestor can continue without waiting for a reply. Paralleling operations, receptions is captured as the receptions attribute.
• Values - represent quantifiable characteristics of a block such as physical and performance characteristics – weight, reliability, etc. This is captured in the values attribute.
• Parts - are the hierarchical composition of the block (the children). This is captured using the built from relationship.
• Flow Ports - specify what can flow in and out of a block. The port name is specified as an attribute on the connects to relationship between the block and a link.
• Standard Ports - specify what behavioral features are required or provided by the block. The port name is specified as an attribute on the joins to relationship between the block and an interface.

While CORE represents the difference between composition and reference ("in, but not of"), this decoration is only shown if diagonal lines are used. If orthogonal lines are used, the composition filled-diamond decoration is shown by default. If diagonal lines are used, each line is marked with a hollow diamond if the wholeMultiplicity on the relationship is 1.

A good reference for further information on BDDs is chapter 7 of A Practical Guide to SysML: The Systems Modeling Language by Sanford Friedenthal, Alan Moore, and Rick Steiner (2012).

Diagram Options

In addition to the classic diagram options, the BDD settings include:

• Use Compact Placement - controls whether a compact placement algorithm is used when laying out the diagram.

• Use Orthogonal Lines - controls whether orthogonal lines or direct lines are used to connect nodes on the diagram.

• Show Role Names - controls whether the part role for the node is shown on the diagram.

• Layout - controls the default diagram layout to use with the diagram. Available diagram layouts options include vertical trees, horizontal trees, and more.

• Levels - controls the initial number of levels to show on the diagram. Individual nodes can then be expanded or collapsed, as desired.

Diagram Palette

The constructs and key entities tabs allow you to quickly develop your block definition, while the all entities tab enables you to relate your blocks to the remainder of your system definition.

• Constructs

• • New Node - drop onto any diagram node to create a new block (component) as part of the node composition (built from)

  • Nodes - drop onto any diagram node to relate an existing block (component) as part of the node composition (built from)

  • New Information Block - drop onto the diagram to insert an information block (a mini property sheet)

  • New Note - drop onto the diagram to insert a new note (descriptive text in a note icon)

  • New Shape - drop onto the diagram to insert a new shape (a rectangle, rounded rectangle, circle, or ellipse with text, if desired)

  • New Graphic - drop onto the diagram to insert a new picture

• Key Entities

• • Component - drop an existing component onto a node to establish any valid relationship. Most often, this will be composition (built from).

• All Entities - all classes and elements in the system model, allowing you to drag any element on top of a diagram node to establish relationships with the balance of your system model

Diagram Menu Commands

• Rename Element

• Renumber Element

• Set Attribute

• Remove Target

• Remove Selection

• Delete Selection

• Select All

• Insert

• Information Block

• Note

• Graphic

• Shape

• Edit Parts

• Edit Role Name

• Layout

• Sort Block

• Open Element view submenu

Tips and Tricks

• To communicate the full technical depth of the block structure, BDDs classically include far more content per node than other diagrams. Make liberal use of the ability to specify different icon templates for each node, using more complete templates where operations/values/ports are desired and lesser templates where they are not. Not only does this tighten the diagram, it helps focus attention on the critical aspects you are seeking to emphasize.