Lecture 6

Question 1

What makes it difficult to maintain consistency between multiple views of a design model?

Answer 1

A design model has multiple views, making it difficult to maintain consistency.

Question 2

What mechanism is widely used to define the language of a design model?

Answer 2

Metamodeling is a widely used mechanism to define such a language.

Question 3

What does a metamodel describe?

Answer 3

A metamodel describes the abstract syntax of a modelling language.

Question 4

What does syntactic consistency ensure in a model’s view?

Answer 4

Syntactic consistency ensures that a model’s view conforms to the model’s abstract syntax.

Question 5

What does semantic consistency require for different views of a model?

Answer 5

Semantic consistency requires different views of a model to be semantically compatible.

Question 6

How are consistency requirements upon a model expressed?

Answer 6

Consistency requirements are expressed using its metamodel and its constraints.

Question 7

When does an inconsistency occur in a model?

Answer 7

An inconsistency occurs if and only if a constraint has been broken.

Question 8

What may a constraint describe in a model?

Answer 8

A constraint may describe syntactic and semantic relationships between model elements.

Question 9

What are some types of constraints that can be described?

Answer 9

Constraints can prescribe coherence relationships between different views of a model, impose best practices, and describe specific requirements.

Question 10

What language can be used to specify consistency constraints?

Answer 10

Object Constraint Language (OCL) can be used to specify consistency constraints.

Question 11

What is an invariant in the context of OCL?

Answer 11

An invariant specifies conditions that must hold in all instances of the class, type, or interface in a UML diagram.

Question 12

What is a precondition or postcondition in the context of OCL?

Answer 12

A condition that must hold at the moment just before or after its execution.

Question 13

What must the passenger size be in relation to the number of seats on a bus?

Answer 13

Passenger size has to be <= number of seats on bus.

Question 14

What must be unique for each passenger in the invariant example?

Answer 14

Each passenger name must be unique.

Question 15

What are the conditions to shift a meeting according to the precondition and postcondition example?

Answer 15

The meeting needs to be not confirmed, shift function parameter needs to be > 0, and d must be >= 1.

Question 16

What is the activity of checking for inconsistencies in design models called?

Answer 16

Detection of inconsistencies.

Question 17

What is the activity for identifying the source, cause, and impact of an inconsistency called?

Answer 17

Diagnosis of inconsistencies.

Question 18

What is required to fix inconsistencies in design models?

Answer 18

Making and propagating changes to different parts of design models.

Question 19

What is the invariant for the variable ‘isMarried’ in the pen and paper exercise?

Answer 19

isMarried must be > int 15.

Question 20

What invariant must hold true at all times for the variable ‘numberOfEmployees’?

Answer 20

numberOfEmployees must be the same as the size of the employee object.

Question 21

What must the Date object ‘d’ be in the pre-context of the function ‘income()’?

Answer 21

The Date ‘d’ must be later than the birthDate.

Question 22

What is the post-context condition for the function ‘income()’ if age < 18?

Answer 22

If age < 18, then result is < 100.

Question 23

What is the post-context condition for the function ‘income()’ if age >= 18?

Answer 23

If age >= 18, then result is < 200.

Question 24

What is the length constraint for a person’s name in the pen and paper exercise?

Answer 24

The length of a person’s name must be always less than 20 characters.

Question 25

What is the OCL expression to ensure a person’s name is less than 20 characters?

Answer 25

Person p : len(p.firstName) < 20.