Chapter 3: SPE and the UML

Question 1

What is UML?

Answer 1

UML is a unified modified language or specifying, visualizing, constructing, and documenting the artifacts of software systems

Question 2

What are UML Class diagrams?

Answer 2

Classes are composed of three components: a name, attributes and operations

Question 3

What are Use Cases?

Answer 3

Use cases describe the behavior of the system or subsystem from the perspective of the user.

Question 4

What does a use case diagram show?

Answer 4

• The set of use cases
• The actors that interact with use cases
• The relationships

Question 5

What are critical use cases?

Answer 5

Use to identify the use cases that have the most effect on the performance of the system.

1. Critical to operation of system
2. Critical to the responsiveness felt by user
3. Critical to risks posed by the system

Question 6

What are scenarios?

Answer 6

A scenario is an instance of a use case.

Scenario shows

• Objects that participate
• Messages that flow between the objects.

Often showed through sequence diagrams

Question 7

What is a sequence diagram?

Answer 7

Sequence diagrams demonstrate the behavior of objects in a use case by describing the objects and the messages they pass.

Question 8

What is the UML stereotype?

Answer 8

A stereotype allows you to create new model elements.

• Derived from existing UML elements
• Specific to a problem domain

Stereotype is created using <> such as <>

Question 9

What is a tagged value?

Answer 9

A tagged value allows you to indicate new properties for model elements.

Tagged value is a pair of values such as processorSpeed = 500MHz

Question 10

What are constraints?

Answer 10

A constraint is a condition or restriction that defines additional model semantics.

Constraint is written in curly braces {}

Question 11

What are stereotypes, tagged values and constraints used for?

Answer 11

To capture more information about the software execution environment

Question 12

What is instance decomposition?

Answer 12

Allows expansion of a high-level sequence diagram to
show lower-level interactions

• To be meaningful the order of the messages on the decomposed instance must be preserved

Question 13

Benefits of instance decomposition?

Answer 13

• Elaborate the sequence diagram as learn more about the system
• Ensure the consistency with the scenario as it was originally described

Question 14

What are references?

Answer 14

references allow for referring to other sequence diagrams

Question 15

How does UML allow specification of time?

Answer 15

1. Timing marks
2. Time expressions
3. Timing constraints

Question 16

What are timing marks?

Answer 16

Denote the time at which a message or event occurs

e.x. message.sendTime() or message.recieveTime()

Question 17

What are time expressions?

Answer 17

Evaluate to an absolute or relative value of time

e.x. after(500ms) or when(t=8:00)

Question 18

What are time constraints?

Answer 18

Express a constraint based on the absolute or relative value of time

e.x. {a.recieveTime() - b.sendTime() < 10 sec}

Question 19

What is the usefulness of time constraints in SPE?

Answer 19

Use time expressions that are meaningful from a performance perspective, such as responseTime() to specifiy performance objectives e.x.

responseTime{j.recieveTime() - i.sendTime() < 5s}

Question 20

How are thread and processes modelled?

Answer 20

1. A parallel process is denoted using the <>

2. A thread being executed with other threads is denoted using <>

Question 21

What are coregions?

Answer 21

Co-region allow an exception to the total ordering of sequence diagrams whereby messages within the co-region are unordered

• Represented using horizontal dividers

Question 22

What is parallel composition?

Answer 22

Indicates sections in sequence diagram that are executed in parallel.

Use the “par” clause in sequence diagram.

Question 23

True or False: Modelling concurrency is important in the early design phases of system?

Answer 23

False, important at the last stages of SPE. Early SPE focuses on models without contention.

Concurrency and synchronization can be looked at a later stage.