Block 2 Glossary

Question 1

Action

Answer 1

An action is an atomic execution (contrast with activity) that results in a change in the state of the model. In an object-oriented context it can be realised by sending a message to an object or by modifying a link or the value of an attribute.

Question 2

Activation

Answer 2

On a sequence diagram, a long rectangle, coincident with the lifeline of an object, showing the entire period when an object is active.

Question 3

Activity

Answer 3

In UML, an activity is an ongoing non-atomic execution (contrast with action) within a state machineor within an activity diagram; in a given context, activities result in one or more actions.

In a software development process, it is a unit of work comprising one or more tasks that someone may be asked to perform.

Question 4

Aggregation

Answer 4

A relationship between an aggregate class and other classes. An aggregate object is an object which can be thought of as being composed of other objects (components), respectively, instances of the other classes. Some authors consider that the objects that are components in one aggregate object cannot be components in another aggregate.

Question 5

Alt

Answer 5

Alternative Fragement

Question 6

Analysis Class

Answer 6

A class that represents structural elements of an initial software solution. Unlike a concept (a domain class), it may define attributes but operations will be added later during design.

Question 7

Analysis Model

Analysis Structural Model

Answer 7

An initial representation of the structure of a software solution by a class diagram; it represents analysis classes, their associations and constraints.

Question 8

Assertion

Answer 8

In DbC, a precondition, a postcondition or an invariant.

Question 9

Association Class

Answer 9

An association that also has class properties. Each instance of the association class defines values for those properties.

Question 10

Association Loop Invariant

Answer 10

An invariant showing the relationship between two paths around a loop.

Question 11

Attribute

Answer 11

A property of an object which is part of the object’s state, and which can be changed. In object-oriented analysis and design, attributes generate accessor methods: one to ‘get’ the value of the attribute and one to ‘set’ or ‘reset’ its value.

Question 12

Baseline

Answer 12

A configuration version singled out as special because it forms a foundation from which further development can progress, typically associated with the major milestones of a project.

Question 13

Bidirectional Association

Answer 13

An association that is navigable in both directions.

Question 14

Business Transcation

Answer 14

A significant activity, episode, interaction, in a business.

Question 15

Cascade Pattern

Answer 15

When designing an interaction diagram to implement a use case, there is a need for an object to send messages to another object with which it does not directly have an association. The Cascade pattern delegates responsibility to another object along a single thread of control (in contrast to the Fork pattern). (See also Law of Demeter.)

Question 16

Check(ing) in

Answer 16

A part of the configuration management process where a specific version (usually the latest) of a configuration item is removed from the configuration repository so that a developer can edit it.

Question 17

Class Diagram

Answer 17

A diagram that shows a set of classes, interfaces and collaborations, as well as their relationships. It is a representation of a structural (or static) model of a domain or of a system.

Question 18

Class Invariant

Answer 18

A constraint that must be true at all times, other than during when one of its methods is executing. A statement about the values of the attributes of a class that must hold for all instances of that class.

Question 19

Class Model

Answer 19

See structural model. A class model is represented in a class diagram.

Question 20

CRC

Answer 20

Class-Responsibilty-Collaboration Cards

An approach to identifying classes and their responsibilities using simply structured cards.

Question 21

Compiler

Answer 21

A software tool that translates (compiles) a program written in one language (the source code) into a program in another language and, in so doing, identifies errors in the source code.

Question 22

Composite State

Answer 22

A state that contains some internal behaviour, which can be represented with a state diagram. (Also referred to as a compound state.)

Question 23

Composition

Answer 23

A form of aggregation with strong ownership; component objects of an aggregate have no life after the destruction of the aggregate.

Question 24

Concept(ual) Model

Answer 24

The structural model that represents the static part of the domain: the concepts and their relationships.

Question 25

Constraint

Answer 25

A limitation on or restriction of behaviour, or structure. In UML, a constraint expresses a rule that governs a model element or a combination of model elements.

Question 26

Constructor

Answer 26

Used to initialise a new object. Technically it is not a method, though it is similar in structure. A constructor handles the dual tasks of allocating memory for the new object and ensuring that this memory is properly initialised. The programmer is expected to provide the code that will accomplish this initialisation. If not, a default constructor will be called that has no parameters and performs default initialisations. In Java, a constructor has the same name as the class in which it appears. Constructors are not members; they are never inherited.

Question 27

Contract

Answer 27

A legal document describing the obligations of two parties entering into an agreement; important contract issues include confidentiality and intellectual property rights. In a software project, a contract exists between the customer (client) and developer (supplier) for the provision of a software product. Also, a way of describing what each task, activity or operation commits to achieve by stating the pre- and postconditions. (See also Design by Contract.)

Question 28

Correct

Answer 28

A correct system is one that meets all its requirements.

Question 29

DbC

Answer 29

Design by Contract The process of developing software based on the notion of contracts between objects, which are expressed as assertions.

Question 30

Defect

Answer 30

A verified lack of conformance to requirements.

Question 31

Defensive Programming

Answer 31

A design philosophy that says preconditions should always be checked. Each operation is responsible for making sure that it is safe to proceed. The checking is placed very close to the code that depends on it.

Question 32

Derived Association

Answer 32

In UML, an association that can be computed from one or more other elements. Although it adds no semantic information, it may aid understanding or be useful for design purposes.

Question 33

Derived Attribute

Answer 33

In UML, an attribute that can be computed from one or more other elements. Although it adds no semantic information, it may aid understanding or be useful for design purposes.

Question 34

Design Decision

Answer 34

Decisions taken during design that may impact on the quality of the software eventually produced.

Question 35

Design Model

Answer 35

A representation of the structure of a software solution by a class diagram; it represents classes, their associations and constraints and their responsibilities in terms of operations.

Question 36

Development Process

Answer 36

A set of rules that define how a software development project should be carried out. It incorporates a life cycle and involves a number of methods and procedures.

Question 37

Domain Expert

Answer 37

Someone who is considered to have a considerable level of knowledge or expertise in a given domain.

Question 38

Domain Model Domain Structural Model

Answer 38

An initial representation of the structure of a domain by a class diagram; it represents domain classes (concepts), and their associations.

Question 39

Dynamic Modelling

Answer 39

Modelling of behaviour as opposed to structure.

Question 40

Dynamic Tool

Answer 40

A tool that is used at run-time.

Question 41

Enumeration Type

Answer 41

A user-defined type with a finite number of literals.

Question 42

Event

Answer 42

In a Java system, an event is an action, such as the user clicking on a button; the system will respond to such an event by carrying out certain actions, provided the program defines an appropriate listener object for that event. In operating systems, an event represents a signal to the CPU to interrupt its operation and switch context. In analysis and design, events are elements of state transition diagrams which cause transitionsbetween states. In UML, an event is a specification of a noteworthy occurence that has a location in time and space. There are four kinds of event in UML: call event: the event of receiving a call for an operation that is implemented by actions on transitions; change event: the event of a Boolean expression becoming satisfied because of a change to one or more of the values it references; signal event: an event that is the receipt by an object of a signal sent to it, which may trigger a transition between two states; time event: an event that denotes the satisfaction of a time expression, such as the occurrence of an absolute time or the passage of a given amount of time after an object enters a state.

Question 43

External Event

Answer 43

An event that links a system to its actors, such as the pressing of a button or the sounding of an alarm. (Contrast with internal event.)

Question 44

Final State

Answer 44

In a state diagram, a special mark (bull’s eye), with only incoming transitions, indicating where processing terminates.

Question 45

Fork (pattern)

Answer 45

When designing an interaction diagram to implement a use case, there may be a need for an object to send messages to another object with which it does not directly have an association. The Fork pattern centralises control in the sender (in contrast to the Cascade pattern). (See also Law of Demeter.)

Question 46

FTR

Answer 46

Formal Techincal Review A process to critique a product of the software development process with a view to improving it. The product might be a customer requirements document, a piece of code, or a test or maintenance plan.

Question 47

Fragment

Answer 47

For our purposes, a way of encapsulating behaviour inside a labelled box. The label can be, for example, opt, alt or loop, standing for optional, alternative and looping behaviour. Sometimes referred to as a frame.

Question 48

Generalisation

Answer 48

A relationship between classes in the object-oriented model that captures the fact that one class of objects is more generalised than another, that is, the methods and data fields of the generalised class (superclass) are a subset of the specialised class (subclass).

Question 49

GRASP

Answer 49

General Responsibility Assignment Software Pattern A collection of patterns which may help the designer assign responsibilities in commonly recurring design scenarios.

Question 50

Glossary

Answer 50

A list of terms or words relating to a particular domain or text, along with an explanation of each term.

Question 51

Grammatical Parse

Answer 51

Used in this module to refer to process for obtaining list of nouns from a written problem description to identify candidate classes.

Question 52

GRASP Creator

Answer 52

A pattern that provides guidance on which class should be responsible for creating new objects.

Question 53

GRASP Expert

Answer 53

A pattern that provides guidance on which class should be responsible for initialising or changing the state of an object.

Question 54

Inheritance

Answer 54

The consequence of a generalisation/specialisation relationship; a subclass inherits the features of the superclass.

Question 55

Initial State

Answer 55

In a statechart diagram, an initial state is a way of indicating the default starting state. An initial state is not a true state; it is a marker with only one outgoing transition to the first state an object finds itself on creation. A statechart diagram must show no more than one initial state.

Question 56

Instance Variables

Answer 56

A data field that is common to all the objects (instances) of a class but the value of which is specific to each object. This contrasts with a class variable (a data field defined as static in Java), whose fixed value is shared by all the instances of a class.

Question 57

Interaction Diagram

Answer 57

A UML diagram that shows the sequencing of messages in an interaction. (See also sequence diagram and communication diagram.)

Question 58

Interface

Answer 58

In general, this refers to the operations (methods), including their syntax and semantics, that a software system/subsystem/module provides to the clients of the system. In the object-oriented approach, the public operations associated with an object are referred to as its interface, or its interface operations. In Java, an interface is a construct similar to a class, which provides a specification (in the form of method headings but no implementation) of the methods for which classes implementing the interface must provide implementations.

Question 59

Internal Event

Answer 59

An event that links the objects within a system, such as the throwing of a language exception. (Contrast with external event.)

Question 60

Internal Transtion

Answer 60

A special transition that does not involve a change of state. An internal transition does not cause the execution of any entry or exit actions.

Question 61

Law of Demeter

Answer 61

A design principle governing the flow of messages among objects. It says that in response to a message m, an object O should send messages only to the following objects: O itself; objects that are sent as parameters to the message m; objects that O creates as part of its reaction to m; objects that are directly accessible from O (using values of the attributes of O).

Question 62

Link

Answer 62

An instance of an association that shows a semantic connection between objects.

Question 63

Message Number(ing)

Answer 63

A means of identifying the ordering of messages in a flow of control. On an interaction diagram, the messages may proceed in a nested or hierarchical fashion. Ambiguity in the message flow is removed by using a multi-stage decimal for each message in an interaction. Thus each message always contains as its prefix the number of the message that gave rise to it. If an object receives a message prefixed 2.6, all messages it sends until it has finished processing 2.6.1, 2.6.2 and so on (this is known as decimal message numbering).

Question 64

Multiplicity

Answer 64

A specification of how many objects of one class are related to one object of another class.

Question 65

Namespace

Answer 65

A boundary within which names are unique.

Question 66

Navigability

Answer 66

Refers to the ability to traverse one or more associations to obtain the object or set of objects associated with an instance of a class through those associations.

Question 67

Navigation Expression

Answer 67

A description of the path taken to traverse the links (corresponding to one or more associations) from one object to another object (or set of objects) or to its (or their) attributes.

Question 68

Non-Deterministic

Answer 68

A situation where one of a number of outcomes is possible, for example when throwing a dice.

Question 69

OCL

Answer 69

Object Contraint Language A text language for specifying constraints, Boolean expressions and queries. OCL can be used to construct expressions for constraints, guards, actions, preconditions, postconditions and assertions. OCL is part of UML.

Question 70

Object Diagram

Answer 70

An instance of a class model that shows objects (possibly value of attributes) and their links at a point in time.

Question 71

Object Model

Answer 71

A collection of objects and their links, where every object in the model is an instance of a class, and each link is an instance of an association in the corresponding class model. An object model is represented by an object diagram.

Question 72

Organisational Units

Answer 72

The groups to which people belong.

Question 73

Package

Answer 73

UML employs the concept of a package to enable the developer to modularise a given system or part of that system. A model comprises a set of packages that hold model elements, such as classes and use cases. A package may contain other packages.

Question 74

Placeholder

Answer 74

Used in this module to refer to the name of a type that is being used as a stand-in until there is sufficient information to make an informed decision.

Question 75

Prototypical Interaction

Answer 75

An interaction described using some prototypical objects.

Question 76

Prototypical Object

Answer 76

An object representing the general case rather than a specific instance.

Question 77

Qualified Assocation

Answer 77

An association that uses attributes of one class to partition the set of objects related to an object across the original association; those attributes are the qualifier of the assocation.

Question 78

Recursive

Answer 78

A recursive association is one between a concept/class and itself.

Question 79

Role

Answer 79

The behaviour of an entity participating in a particular context. It may also refer to the behaviour of people in a domain.

Question 80

Role Name

Answer 80

The identification of a specific role for a class in a given association.

Question 81

Self-Transition

Answer 81

In a state machine, this is a transition that originates in one state and returns to the same state. They are commonly used to model loops or cycles.

Question 82

Sequence Diagram

Answer 82

A UML interaction diagram that focuses on the time-ordering of the messages.

Question 83

Signature

Answer 83

In general, the combination of name, parameters and return type of an operation. In Java, the combination of name and formal parameters in a method heading (that is, excluding method’s return type).

Question 84

Simple State

Answer 84

A state that contains no substructure. (See also composite state.)

Question 85

Snapshot

Answer 85

A representation (using a UML object diagram) of objects and their links at a certain instant in time.

Question 86

Software Engineer

Answer 86

A person employed to undertake software engineering.

Question 87

Specialisation

Answer 87

A relationship between classes in the object-oriented model that captures the fact that a child class is a subtype of the parent class, that is, the methods and data fields of the specialised class (subclass) are a superset of the generalised class (superclass specialised class).

Question 88

State

Answer 88

A condition or situation during the lifetime of an object during which it satisfies some condition, performs some activity or waits for some event. In object-oriented terms, it is the value of an object’s attributes. From the client’s point of view, the state of an object is implemented in terms of methods(that is, its accessor methods). However, inside the object’s class definition, the accessor methods may be implemented in terms of private instance variables which are used to store the state (although on occasion the implementation may be in terms of methods which calculate the state). In formal specification, it refers to the stored data that a system accesses and alters.

Question 89

Statechart

Answer 89

Formalism introduced by David Harel for the representation of complex state transitions; it was adopted by the UML in its state machines.

Question 90

State-Depenent State-Independent

Answer 90

An object that always responds in the same way to a given event is state-independent. In contrast, objects that react differently to a given event are state-dependent.

Question 91

State Machine

Answer 91

A specification of the sequences of states that an object goes through in response to events during its life, together with its responsive actions. A state machine is attached to a source class, collaboration or method and specifies the behaviour of the instances of the source elements. State machines are represented in UML by state diagrams.

Question 92

Static Analysis Tools

Answer 92

Tools that allow software or other development artefacts to be checked for some properties or tested at compile time.

Question 93

Subclass

Answer 93

In object-oriented terms, the subclass inherits from the superclass, or parent class. In Java, all classes are subclasses of Object. A subclass may define its own methods and data fields in addition to those that are inherited. It may also override any of its inherited methods.

Question 94

Substitutability

Answer 94

Substitutability means that an object of one type is legitimately substitutable for an object of another type. This is allowed in Java when objects are related through inheritance (that is, an object of the child class may be substituted for an object of the parent class). However, substitutability is only sensible when the objects are related as subtype to supertype (that is, when the inheritance is inheritance for specialisation and not inheritance for construction).

Question 95

Superclass

Answer 95

In Java, the (parent) class that is extended by another class (the child class or subclass).

Question 96

System Class

Answer 96

In analysis, a class with a single instance that represents the whole system.

Question 97

System Operation

Answer 97

An operation executed by a software system as a response to an external event.

Question 98

Tangible Objects

Answer 98

Physical objects identified during modelling.

Question 99

Tier

Answer 99

A physical partitioning of a system.

Question 100

Use Case Object

Answer 100

An object which is an instance of a class defined for each use case. In a hotel system, for example, there might be classes such as CheckerIn, CheckerOut and RoomMover. Each would have a method with a name like run(). The user interface would then create a single instance of the appropriate class, initialise it suitably, and then send it the run() message.

Question 101

Use Case Realistation

Answer 101

An activity that consists of linking the use cases to the classes which are going to carry them through.

Question 102

Value Identity

Answer 102

The identity of a real-world object; how people distinguish between objects using identifiers with values which are understood by other people.

Question 103

Visibility

Answer 103

The property of where named elements can be accessed in a program.