Supplementary: Using and Extending UML

CSE870: Advanced Software Engineering: Extending and Using UML (Cheng, Sp2003)

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Supplementary:

Using and Extending UML


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RExtensibility Mechanisms

• Stereotypes

• Tagged Values

• Constraints ActionQueue

<<container>>

{version = 3.2}

add(a: Action)remove(n: Integer)

{add runs in O(1) time}


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RStereotypes

• Extends the UML vocabulary

• Create new building blocks derived from existing ones,– specific to problem domain– Example: Sensors for embedded systems,

<<sensor>>

thermometer

temp

read

<<sensor>>

Voltage meter

volt

read


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RTagged Values

• Extends properties of UML building block

• Create new information in that element’s spec

• Example: {version, author values for Software Class} <<sensor>>

Voltage meter

volt

read

{reader=J. Smith}


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RConstraint

• Extends the semantics of a UML building block

• Add new rules or modify existing ones– Example: {ordered constraint on a add

operation for a Queue}

<<sensor>>

Voltage meter

volt

read

{reader=J. Smith}

{read before thermostat check}


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RInterface

• Interface: collection of operations that specify a service of a class or component– Externally visible behavior of that element– Set of operation specs (signatures)– Not a set of operation implementations


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RInterface Example

• Interface specifies desired behavior of an abstraction independent of implementation

• Specifies contract• May also create

stereotype to further define behavior– No attributes– Only operations

• (visibility, concurrency, stereotypes, etc.)

Wordsmith.dll

ISpellIThesaurus

IUnknown

<<interface>>URLStreamHandler

openConnection()Parse URL()setURL()toExternalForm()

Operations


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RDependency Relationship

• Definition: – some set of model elements requires presence of another set

of model elements – for semantic completeness or correctness

• Examples: – <<realize>>: between type and class– <<trace>>: analysis class and design class– <<create>>: source class creates a target class instance– <<access>>: permission of one pkg to access public elements

of another– <<bind>>: reln between parameterized model elt with formal

parameter list and that model elt bound to actual parameters. (e.g., templates in C++)


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RDependency Example

QueueBasetype, size

QueueString, 400

Integer Queue

<<bind> <integer, 1000>

Explicit Parameterization

Formal parameter list

Actual parameter list


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Metamodels


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RClass Diagram Metamodel


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RObject ModelObject Model

• Creation Tips– understand the problem– keep it simple at first, then refine later– choose class names carefully– try to have only binary relations– do not worry about multiplicities on first draft– do not feel you have to use all constructs– concentrate on WHAT– document reasons behind the model– refine until complete and correct


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RDynamic ModelDynamic Model

• Creation Tips– only construct state diagrams for object classes with meaningful

dynamic behavior– verify consistency between diagrams for shared events– use scenarios to begin the construction of diagrams– let application decide on granularity and distinguish between

actions and activities– make use of entry and exit actions for multiple transitions– use nested states to improve understanding/readability– distinguish state diagrams for super and subclasses– watch for race conditions in the diagrams


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Approaching a Problem

Where do we start?

How do we proceed?


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RWhere Do We Start?

• Start with the requirements– Capture your goals and possible constraints– Environmental assumptions

• Use-case analysis to better understand your requirements– Find actors and a first round of use-cases

• Start conceptual modeling– Conceptual class diagram– Interaction diagrams to clarify use-cases– Activity diagrams to understand major processing

Requirements Elicitation and Analysis


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RHow Do We Continue?

• Refine use-cases– Possibly some “real” use-cases

• Using interface mockups

• Refine (or restructure) your class diagram– Based on your hardware architecture

• For instance, client server

• Refine and expand your dynamic model– Until you are comfortable that you understand the

required behavior

• Identify most operations and attributes

High-Level Design


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RHow Do We Wrap Up?

• Refine the class diagram based on platform and language properties– Navigability, public, private, etc– Class libraries

• Identify all operations– Not the trivial get, set, etc.

• Write a contract for each operation• Define a collection of invariants for each class• Implement

Detailed Design and Implementation


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RWhy is requirements analysis difficult?

• Communication: misunderstandings between the customer and the analyst– Analyst doesn’t understand the domain– Customer doesn’t understand alternatives and

trade-offs

• Problem complexity– Inconsistencies in problem statement– Omissions/incompleteness in problem statement– Inappropriate detail in problem statement


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RWhy is requirements analysis difficult?

• Need to accommodate change– Hard to predict change– Hard to plan for change– Hard to predict the impact of change


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RFirst Law of Software Engineering

“No matter where you are in the

system lifecycle, the system will

change, and the desire to change it

will persist throughout the lifecycle.”


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RReasons for changing requirements

• Poor communication• Inaccurate requirements

analysis• Failure to consider

alternatives• New users• New customer goals

• New customer environment

• New technology

• Competition

• Software is seen as malleable

Changes made after the requirements are approved increase cost and schedule


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RRequirements Products

• Specification document– Agreement between customer and developer– Validation criteria for software

• Preliminary users manual

• Prototype– If user interaction is important– If resources are available

• Review by customer and developer – Iteration is almost always required


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RAnalysis: Steps to follow

• Obtain a problem statement• Develop use cases (depict scenarios of use)• Build an object model and data dictionary• Develop a dynamic model

– state and sequence diagrams

• Verify, iterate, and refine the models• Produce analysis document


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RUse Cases

• High-level overview of system use• Identify scenarios of usage• Identify actors of the system:

– External entities (e.g., users, systems, etc.)

• Identify system activities• Draw connections between actors and

activities• Identify dependencies between activities (i.e.,

extends, uses)


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RAnalysis: Object Model

• Organization of system into classes

connected by associations

– Shows the static structure

– Organizes and decomposes system into

more manageable subsystems

– Describes real world classes and

relationships


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• Object model precedes the dynamic model

because

– static structure is usually better defined

– less dependent on details

– more stable as the system evolves


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• Information comes from– The problem statement and use cases– Expert knowledge of the application

domain• Interviews with customer• Consultation with experts• Outside research performed by analyst

– General knowledge of the real world


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RObject Model: Steps to follow

• Identify classes and associations

– nouns and verbs in a problem description

• Create data dictionary entry for each

• Add attributes

• Combine and organize classes using

inheritance


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RAnalysis: Dynamic model

• Shows the time dependent behavior of the system and the objects in it

• Expressed in terms of– states of objects and activities in states– events and actions

• State diagram summarizes permissible event

sequences for objects with important dynamic

behavior


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RDynamic Model: Steps to follow

• Use cases provide scenarios of typical interaction

sequences

• Identify events between objects (Sequence

Diagram)

• Prepare an event trace for each scenario

• Build state diagrams

• Match events between objects to verify

consistency


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RAnalysis: Iteration

• Analysis model will require multiple passes to complete

• Look for inconsistencies and revise

• Look for omissions/vagueness and revise

• Validate the final model with the customer

Supplementary: Using and Extending UML

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