Unified Modeling LanguageUser Guide

Section 2—Basic Structural Modeling

Chapter 4—Classes

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Overview• Classes

– Attributes– Operations– Responsibilities

• Modeling the vocabulary of a system.• Modeling the distribution of responsibilities.• Modeling non-software “things”.• Modeling primitive types.• Modeling quality abstractions.

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Classes

• Description of a set of objects that share the same attributes, operations, relationships, and semantics.

Windoworiginsize

open()close()

nameattributes

operations

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Names

• Distinguishing identity.

• Textual string.

• Simple name.

• Prefixed by package name to generate path name.

Customer

Account

TemperatureSensor

Circuit

Java::awt::RectangleSimple names

path name

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Name Rules

• Consists of letters, numbers, and certain punctuation marks.

• Short noun phrases drawn from vocabulary of the domain.

• First letter of every word capitalized.TemperatureSensor

BrokerageAccount

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Attributes

• Named property of a class.• Describes a range of values that an instance

of the property may hold.• Short noun representing property of its

enclosing class.• First letter of every word capitalized except

the first.birthDateuserAccount

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Attributes (cont’d)

attributesheight : Floatwidth : FloatisStudent : Boolean = false

originsize

You can further specify an attribute by stating its class and possibly a default initial value

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Operations• Abstraction of something that can be done to

an object.• Shared by every object of the same class.• May cause object to change state.• Short verb representing behavior of

representing class.• First letter of every word capitalized except the

first.addUser()isEmpty()

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Operations (cont’d)

operations reset()setAlarm( t : Temperature )value() : Temperatureadd()

move()

You can specify an operation by stating its signature, covering the name, type and default value of all parameters and a return type

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Organizing• Only a subset of attributes and operations are

typically relevant to any one view.• Elide a class; hide non-relevant information.• Use stereotypes to

categorize.• Use ellipsis to specify

additional attributes oroperations

<<constructor>>new()new( p : Policy )<<process>>process( o : Order )…<<query>>isSuspect( o : Order )

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Responsibilities

• Contract or obligation of a class.

• Carried out by attributes and operations.

• Techniques– CRC cards (Class-Responsibility-

Collaborator);Kent Beck and Ward Cunningham; ’89

– Use case based analysis.

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Responsibilities (cont’d)

• Free-form text; one phrase per responsibility.

Responsibilities-- determine the risk of a customer order-- handle customer-specific criteria for fraud

FraudAgent

responsibilities

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Modeling Techniques

• Vocabulary.

• Distribution of responsibilities.

• Non-software things.

• Primitive types.

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Modeling Vocabulary

• Things used to describe the problem or solution. Found through CRC cards and/or use case analysis.

• Identify responsibilities for each abstraction.

• Provide attributes and operations needed to carry out responsibilities.

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Modeling Distribution of Responsibilities

• Identify a set of classes that work together to carry out some behavior.

• Identify responsibilities for each class.• Split classes with too much responsibility.• Collapse classes with trivial responsibility.• No class should do too little or too much.

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Modeling Non-software Things

• Model the thing as a class.

• Use stereotypes to give a distinctive cue.

• Consider nodes to model hardware.

• Use a unique icon.

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Modeling Primitive Types

• Model as a type using a class notation.

• Use stereotypes as necessary.

• Use constraints to represent valid values.<<enumeration>>

Boolean

falsetrue

<<datatype>>Int

{ value range –2**31 to +2**31-1}

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Hints & Tips

• Well-structured class– Provides a crisp abstraction drawn from

vocabulary of problem or solution.– Embodies small, well-defined set of

responsibilities.– Provides clear separation of the abstractions

specification and implementation.– Understandable and simple.– Extensible and adaptable.

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Hints & Tips (cont’d)

• Drawing a UML class– Show only properties that are important in

a specific context.– Organize long lists of attributes and

operations by grouping.– Show related classes in the same

diagrams.

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Summary• Classes

– Name.– Attributes.– Operations.– Responsibilities.

• Modeling techniques.– Vocabulary.– Responsibilities.– Non-software things.– Primitive types.