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CS3773 Software Engineering. Lecture 04 UML Class Diagram. Class and Object. Objects are discrete entities with well defined boundaries and encapsulate States Behaviors Classes represent types of objects that share a set of features: attributes, operations, and relations - PowerPoint PPT Presentation
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CS3773 Software Engineering
Lecture 04UML Class Diagram
UTSA CS37732
Objects are discrete entities with well defined boundaries and encapsulate
– States– Behaviors
Classes represent types of objects that share a set of features: attributes, operations, and relations
Classes describe key concepts involved in the problem domain
Classes are basic building blocks of OO system
Class and Object
UTSA CS37733
Elements of class diagram:– Class represented as a box containing three
compartments Name Attributes Operations
– Relation represented as a line between two classes Association Generalization Aggregation and composition
UML Class Diagram Syntax
UTSA CS37734
UML class diagrams can be used in three distinct ways depending on the phase of system development:
– Conceptual (Domain Models) Requirements phase
The diagram represents the problem that the software should solve
Classes are real-world concepts in the system's environment
Not necessarily a direct mapping to how these will be implemented (although they may end up being classes in the software system)
Class Diagram: Perspectives
UTSA CS37735
– Design The diagram is complete: both attributes and operations
The diagram depicts only the interfaces of software classes, but still avoids implementation details (information hiding)
– Implementation The diagram depicts interfaces and implementations of classes
Class Diagram: Perspectives
UTSA CS37736
Class
Classes are entities from the problem domain– Actors that interact with system
– Any information that the system stores, analyzes, transforms, displays, etc.
– Transient objects
e.g., business transactions, phone conversations, etc.
Classes are named, usually, by short singular nouns
Syntax: A box with three compartments for names, attributes, and operations respectively
UTSA CS37737
Class Diagram – An Example
Class Diagram – An Example
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Identifying Class
Classes are usually derived from the use cases for the scenarios currently under development
Brainstorm about all the entities that are relevant to the system
Noun Phrases– Go through the use cases and find all the noun phrases
– Watch out for ambiguities and redundant concepts
UTSA CS37739
Attribute
Attributes are simple data associated with a class
e.g., integer, sets, dates
Attributes are properties of a class
Attributes are information that distinguishes one instance of the class from another instance
They are distinguishing characteristics of the objects
Syntax: name: type = default value
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Operation
Operations are the responsibilities/services of an object in the class
Operations query or transform values of object's attributes, change state
A class's attributes and operations document the purpose of the class --- what information it maintains, and how that information can be manipulated
Syntax: name (parameters) : return-type
UTSA CS377311
Static Attribute and Operation
Static attributes model data values shared by all objects of the class
e.g., number of objects
Static operations are class-related operations not offered by instances of the class
e.g., “create ()”, “search ()”
Syntax: underlined attribute or operation
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Association
An association is a relationship between classes
An association is a name, usually short verb – Some people name every association
– Others name associations only when such names will improve understanding
e.g., avoid names like “is related to”, and “has”
An association represents different types of relationships
e.g., data flow, requests, parts of compound class
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Association Syntax
An association may have– An association name
– Multiplicity
– Role names
– Qualifier
– Association class
– Navigability
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Multiplicity
Multiplicities on associations give lower and upper bound on the number of instances of the local class that can be linked to one instance of the remote class
Syntax: 1, *, etc. at the association end. Examples:– * (zero or more)
– 1 .. * (one or more)
– 1 .. 40 (one to 40)
– 5 (exactly 5)
– If no multiplicity is specified, the default is 1
UTSA CS377315
Multiplicity
Multiplicities on classes indicate how many instances of the class can be at run time
Multiplicities constrain the number of objects
Syntax: 1, *, etc. at the top right corner of class
UTSA CS377316
Role Name
Is a part of association
Describes how the object at the association end is viewed by the associated object
Is useful for specifying the context of the class
Syntax: name at the association end
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Qualified Association
Qualified association is an association key that identifies the object at the other end of the association
Qualifier is a key or index used to identify one or fewer objects from set of many objects
Qualifier is often an attribute of the class at the other end of the association, and the attribute is recognized as uniquely identifying one or fewer objects of the class.
Syntax: name in box at the end of an association
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Association Class
Association class allows to add attributes, operations to an association
The association contains more information
Syntax: class connected to the association by a dashed line
Constraint: only one instance of association class between any two associated objects
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Generalization
Indicates an “is-a” relationship
All instances of the subclass are instances of the super class
A subclass inherits all attributes, operations and associations of the parent
The common attributes and operations are placed in the superclass; subclasses extend the attributes, operations, and associations as they need them
Syntax: open triangle at the superclass end of the association
UTSA CS377320
Aggregation
Indicates a loose “has-a” relationship
The compound class is made up of its component classes
Represents the “whole-part” relationship, in which one object consists of the associated objects
– The whole controls the relationship
– The part services requests from the whole
Syntax: hollow diamond at the compound class end of the association
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Aggregation Semantics
Whole can exist independently of the parts
Part can exist independently of the whole
Whole is incomplete if some of the parts are missing
It is possible to have shared ownership of the parts by several wholes
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Composition
Composition is a particular kind of aggregation
Component classes are physically part of the compound class
e.g., a car is composed of an engine, wheels, etc.
The component class dies if the compound class dies
Syntax: filled diamond at the compound class end of the association
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Composition Semantics
Component belong to exactly one compound at a time
Compound is responsible for the creation and destruction of all its components
Compound may also release its components to other compounds
If the compound is destroyed, it must either destroy all its components, or give responsibility for them over to some other classes
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Review of Class Diagram
Class is a set of discrete entities that share the same features
Class encapsulates data (attributes) and functions (operations: queries of modifiers)
Multiplicity constrains the number of objects participating in a relationship at any point in time
Relationship represents connections between classes – Association: role name, qualifier, association class,
navigability
– Generalization
– Aggregation and composition
UTSA CS377325
UML Object Diagram
Object is an instance of some class
Object diagram is a snapshot of the objects in a system
Object diagram represents all the instances of classes (objects) and their associations (links) at a point of time
Object diagram gives better feeling of problem by showing examples
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UML Object Diagram Syntax
Object is a box with two compartments: object name and attributes
Objects name is underlined– Class name alone
– Object name alone
– Object name concatenated with the class name, separated by a colon
– Name convention: starting with a lowercase letter
Relations among objects are represented as links
UTSA CS377327
UML Object Diagram – An Example
Ann: Patron
Jo: Patron
Tom: Patron
A: Book
: Book1
: Book2
: Book
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Reading Assignments
UML 2 and The Unified Process – Chapter 7, “Objects and classes”– Chapter 8, “Finding analysis classes” – Chapter 9, “Relationships”– Chapter 18, “Refining analysis relationships”
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