03 - SysML

Question 1

What are some key advantages of Model-Based Systems Engineering (MBES)?

Answer 1

• Shared understanding of system requirements and design
• Assists in managing complex system development
• Improved design quality
• Supports early and ongoing verification & validation to reduce risk
• Provides value through the life cycle (e.g., training)
• Enhances knowledge capture
• Primary artifact is system model,
• Other artifacts are secondary

Question 2

Explain “Shared understanding of system requirements and design” in MBES.

Answer 2

• Validation of requirements
• Common basis for analysis and design
• Facilitates identification of risks

Question 3

Explain “Assists in managing complex system development” in MBES.

Answer 3

• Separation of concerns via multiple views of an integrated model
• Supports traceability through hierarchical system models
• Facilitates impact analysis of requirements and design changes
• Supports incremental development & evolutionary acquisition

Question 4

How does MBES improve design quality?

Answer 4

• Reduces errors and ambiguity
• Provides a more complete representation.

Question 5

Explain the view on artifacts in MBES.

Answer 5

• The primary artifact is the system model, an integrated, coherent, consistent view created using dedicated systems modeling tools.
• Other artifacts are secondary, automatically generated from the system model and using the same modeling tool.
• The system model serves as a central repository for design decisions.
• Each decision is captured as a model element (or a relationship) in a single place within the system model.

Question 6

Describe modelling languages in MBSE.

Answer 6

Grammar - semiformal language that defines

• Elements you are allowed to put into your model
• Allowable relationships
• Set of notation you can use to display the elements and relationships on diagrams

Question 7

Describe modeling methods in MBSE.

Answer 7

• Set of design tasks that a modelling team performs to create a system model
• Design tasks that ensure that everyone on the team is building the system model consistently

Question 8

Design modelling tools in MBSE.

Answer 8

• Designed to comply with the rules of one or more modelling languages
• Enabling users to construct well-formed models in those languages
• Different from diagramming tools (Visio) -> creation of diagrams with no model underlying those diagrams
• Modification in a modelling tool changes the underlying model’s element, updating all the other diagrams with that element.

Question 9

What are two modelling needs?

Answer 9

• System-of-Systems
• Multiple Levels

Question 10

Briefly describe SysML.

Answer 10

• Graphical modelling language
• Subset of UML 2 with extensions
• Model and data interchange via XML Metadata Interchange
• Semantics = meaning, Notation = representation of meaning
• Methodology and tool independent

Question 11

Name the three main diagram types that compose a SysML diagram.

Answer 11

• Behavior Diagram
• Requirement Diagram (New from UML 2)
• Structure Diagram

Question 12

What are the subtypes of diagrams inside a Behavior Diagram?

Answer 12

• Activity Diagram (Modified from UML 2)
• Sequence Diagram
• State Machine Diagram
• Use Case Diagram

Question 13

What are the subtypes of diagrams inside a Structure Diagram?

Answer 13

• Block Definition Diagram (Modified from UML 2)
• Internal Block Diagram (Modified from UML 2) -
  –one type —>Parametric Diagram (New from UML 2)
• Package Diagram

Question 14

Explain a Package Diagram.

Answer 14

• Expresses information about the structure of a system model (a package containment hierarchy).
• Conveys the logical groupings of model elements.
• Organizes the model
  • By system hierarchy
  • By diagram type
  • Using viewpoints to augment model organization

Question 15

Explain a Block Definition Diagram.

Answer 15

• Primary type of diagram to communicate structural information about a system
• Expresses types of structures that can exist internally and externally
• Describes the relationship among blocks (composition, association, specialisation)
• Generalizes relationships between elements, allowing hierarchy and design abstractions

Question 16

Explain an Internal Block Diagram.

Answer 16

• Contrary to a Block Definition Diagram (BDD) where a block is a black-box, blocks are represented as white-box implementation
• Complements the information in BDD
  • Shows connections between blocks
  • Describes services that interact with\ one another
  • Defines types of matter, energy, and data that can flow among them across their connections.

Question 17

Explain a Parametric Diagram.

Answer 17

Type of Internal Block Diagram.

• Expresses a set of constraints
  • Generally, equations and inequalities
  • Determine the values that are valid in a system that is operating nominally
• Expresses equations between value properties, providing support for engineering analysis and identification of critical performance properties
• Represents the usage of the constraints in an analysis context
• Focuses on the flow of matter, energy, and data
• Specifies transformation of inputs to outputs
• Can create call behavior actions in an activity to model behavioral decomposition
• Allows model asynchronous communication among structures within a distributed system.
• Wait time actions can be used for periodic behaviors
• Activity partitions allow for activity’s actions responsibility allocation to specific structures within a system

Question 18

Explain an Activity Diagram.

Answer 18

Explains how an input is processed, serving as a problem description. It can show parallel sets of activities.

Question 19

Explain a State Machine Diagram.

Answer 19

• Expresses information about a system’s state-based behavior response to event occurrences
• Usually depicts the life cycle of a block
• Supports event-based behavior
  • Transition with trigger, guard, action
  • State with entry, exit, and do-activity
  • Can include nested sequential or concurrent states
  • Can send/receive signals to communicate between blocks during state transitions
• Has three event types
  • Change event
  • Time event
  • Signal event
  -

Question 20

Explain a Use Case Diagram.

Answer 20

• Black-box view of the services that a system provides
• Provides means for describing basic functionality in terms of usages/goals of the system by the actors
• Serves as system context diagrams
• Displays the generalizations among actors and use cases
• Displays the included relationships and extended relationships among use cases

Question 21

Explain a Sequence Diagram

Answer 21

• Present information about a system’s behavior over time, focusing on the communications occurring among specific system parts.
• Often used to model a test case. A single execution path through a use case with specified input values and expected output values.
• Ability to completely and unambiguously specify a system behavior
• Conveys all three essential pieces of information
  • The order of the behaviors that occur
  • Which structure performs each behavior
  • Which structure invokes each behavior
• Server as inputs into the development stage of the system life cycle
• Provides representations of message-based behavior, to represent the flow of control and describe the interaction between parts
• Provides mechanisms for representing complex scenarios, allowing reference sequences, control logic and lifeline decomposition

Question 22

Explain a Requirement Diagram.

Answer 22

• A requirement stereotype represents a text-based requirement
  • Includes an id and text properties
  • Can add user-defined properties such as a verification method
  • Can add user-defined requirements categories
• Requirements hierarchy describes requirements contained in a specification