System Design: Architectures and Archetypes models Code Translation according to ... “The Unified Modeling Language is a language for ... Class Diagram State Diagram

Stephen J. MellorProject Technology, Inc.http://www.projtech.com

Stephen J. MellorProject Technology, Inc.http://www.projtech.com

System Design:Architectures and

Archetypes

2

PROJECT TECHNOLOGY, INC.

System Design: Architectures and Archetypes

This tutorial shows you how to:v identify the characteristics that

determine the system design;v engineer the system-wide design

to meet performance constraints;v model the system-wide design—

the software architecture;v build archetypes to produce

efficient code.

3


Application-Independent Software Architecture

PhysicalTelephone

OffHook

OnHook

ApplicationModel

ArchitectureCode

4


Properties

Separation ofapplication fromarchitecture

ExecutableUML models

Code

Translationaccording torules

5


What’s in the Architecture?

The architecture comprises:v an execution engine plusv a set of archetypes.

Execution Engine Archetypes

6


Archetypes

Archetypes define the rules for translating the applicationinto a particular implementation.

.Function Class Class ${Class.name} : public ActiveInstance { private: .invoke PrivateDataMember( Class )… …

};

placeholder introduced by ${...}

text(whichhappens to beC++)

.Function PrivateDataMember( inst_ref class )

.select many PDMs from instances of Attribute related to Class.for each PDM in PDMs${PDM.Type} ${PDM.Name};.endfor

7


Application-Independent Software Architecture

The software architecture is independent of thesemantics of the application.

This offers:v early error detection through verificationv reuse of the architecturev faster performance tuningv faster integrationv faster, cheaper retargeting

Table of Contents

The Software Architecture

Architectural Styles

Selecting an Architecture

Performance Requirements

Executable Domain Models

Model Execution

Capturing the Models

Archetype Language

A Direct Translation

Specifying the Architecture

An Indirect Translation

System Construction

The Shlaer-Mellor Method

The Software Architecture

10


Challenges of Real-Time Development

How can we both:v provide required

functionalityandv meet real-time

performanceconstraints?F (Re-)organize

the software.

11


Software Architecture

v datav controlv structuresv time

The abstract organization of software is called thesoftware architecture.

It proclaims and enforces system-wide rules forthe organization of:

12


Data

v tables or arrays?v special purpose structures

such as trees, linked lists?v independent?

and access to them:v direct access by name or

pointer?v indirect access through

functions that encapsulate thedata structure?

The architect prescribes the storage scheme for data elements:

Instances stored as a tree

13


Control

The architect prescribes control:v what causes a task to

execute?v what causes a task to

relinquish control?v what is the next function to

execute within a task?v how to coordinate multiple

tasks accessing commondata to ensure dataconsistency?

Task 1 Task 2

access

Shared data area

14


Structures

The architect prescribes howto package code and data in:v tasks?v functions?v shared data areas?v classes?

and the allocation criteria forallocating parts of theapplication to these structures.

Application domain

Task 1 Task 2

Shared data area

15


Time

v absolute timev relative time

The software architect prescribes howto provide time-related services:

16


Uniformity

v reduces cost ofunderstanding, building,and maintaining thesoftware

v decreases integration effortv leads to smaller, more

robust code

A minimal, uniform set of organization rules:


18



v Monitor and controlv Transportersv Transactions

Real-time and embedded systemscommonly employ (parts of) threemajor architectural styles:

19


Monitor and Control

v set control pointsin the hardwarewith desiredvalues

v read values fromhardware forcomparison ordisplay

This style comprises a collection of related control loops that:

20


Monitor and Control

v Manufacturing systems(Aluminum rolling mill)

v Embedded microprocessorcontrol systems(automobiles)

v Household microprocessor(temperature control)

•Real-time control systems (Fly-by-wire aircraft)

21


Monitor and Control

This style tends to have:v hard response deadlinesv data that must have

current valuesv significant computation

on the data

22


Transporters

Transporters:v move data from one

place to anotherv are responsible for

routing data, but notfor the data content

v may split or re-assemble the datapackets

23


Transporters

v telephonyv telemetry

v off-line transaction processing(credit card processing)

v data collection and archivingsystems

24


Transporters

Transporters:v must meet throughput

requirementsv may have response time

requirements on somestreams

v have persistent applicationdata describing routing

v must manage bufferscontaining applicationpackets

25


Transactions

Transactions:v maintain a picture of a real or

hypothetical worldv accept requests to query or

update the picturev perform some amount of

computationv send responses to the

outside world based onthe computation

26


Transactions

v on-line bankingv reservation systemsv simulatorsv desktop applications

(word processors,spreadsheets)

27


Transactions

This style tends to have:v considerable persistent

application datav variable response timesv significant throughput

requirements

28


Hybrids

Many systems use several styles.

General Purpose

Ejection

Injection

Operator Controls

NetworkComputer

Transaction

MonitorandControl

Transporter

Selecting an Architecture

30


Characterize the System

“[E]very design problem begins with an effort toachieve a fitness between two entities: the form inquestion and its context. The form is the solutionto the problem; the context defines the problem.In other words, when we speak of design, the realobject of discussion is not the form alone, but theensemble comprising the form and its context.Good fit is a desired property of this ensemblewhich relates to some particular division of theensemble into form and context.”

Notes on the Synthesis of FormChristopher Alexander

31


The External World

Understand and quantify theexternal world in terms of:v rate and volume of

events originating in theexternal worldw normal quiescent ratesw burst rates in periods of

unusual demand

v its natural periodicitiesv how frequently data

elements change values

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Non-Localized Requirements

Requirements Meetingv continuous 24 x 7 operationv fault tolerance and recoveryv personnel and equipment safety

33


Business Constraints

Understand andenumerate anyconstraints thebusiness may placeon the architecture.

• number / location of processors• upward compatability• choice of hardware platforms• choice of software platforms

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System Sketch

v processorsv communication

channelsv bandwidthv external actorsv protocols

Document the system with a sketch to capture:

to provide a reference basis for both the clientand the architect.

DMA

Single ProcessorDemand Tasks

Periodic

Performance Requirements

36


The High Spots

“It is common practice in engineering, if we wishto make a metal face perfectly smooth, to fit itagainst the surface of a metal block which islevel within finer limits than we are aiming at, byinking the surface of this standard block andrubbing our metal face against the inked surface.If our metal face is not quite level, ink marksappear on it at those points that are higher thanthe rest. We grind away at these high spots...”

Notes on the Synthesis of FormChristopher Alexander

37


Monitor and Control

Determine the sampling time(s).

The external process may be:v naturally periodic

v continuous

v loosely coupled

impose period based on fastest data

use natural period

impose period based on longest acceptable delay

100 MS 400 MS

spill background

Presence of beam

A naturally periodicsystem may requiresampling at several

points in the waveform.

38


Transporters

Streams* may have packets* that can be:v state-dependent, orv throttled, orv ignored with impunity

For the worst case, figure:• throughput requirements• response-time requirements

for each stream.

* A stream is a source of packets.* A packet is some piece of information (control or data).

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Transactions

Threads* may be either:v time-criticalv at operator speedsv at will

Throughput, then, is:• subordinate to the critical threads• important on the average• the design goal

* A thread is all the work done as a result of some stimulus.

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Performance Quantification

To quantify performance requirements in an analysis:v Identify critical threadsv Identify worst burstsv Identify the required processing for each

Only do this for the“high spots!”

Executable DomainModels

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Unified Modeling Language

“The Unified Modeling Language is a language forspecifying, constructing, visualizing, anddocumenting the artifacts of a software-intensivesystem.”

The UML Summary

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© 1998 Model Integration, LLC

UML Models

Unified Modeling Language (UML) addresses the followingdevelopment tasks:

Requirements

Analysis

Design

requirements analysis (external usage)

system modeling (data, control, algorithm)

system deployment (allocation to processors)

44



UML Model Notation

UML defines a notation for the following models.Use Case Diagram: system stimulus-response modelStatic Structure Diagram: package, class, and object modelsState Diagram: control for dynamic behaviorActivity Diagram: workflow of activitiesSequence Diagram: dynamic interactions with timeCollaboration Diagram: dynamic interactions without timeComponent Diagram: software componentsDeployment Diagram: allocation of components toprocessing elements

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Use of UML Models

u Essential Models capture the complete scope and behavior ofthe system and support model translation to code.

u Auxiliary Modelsaugment theessential models.

u Derived Models show additionalviews of the essentialmodels.

Package DiagramClass DiagramState Diagram

Processing Spec

Essential Models

Collaboration DiagramSequence Diagram

Derived Models

Use Case DiagramComponent DiagramDeployment Diagram

Auxiliary Models

UML Models

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Class Diagram

Abstract classes based on both:v data, andv behavior

Recipe

Recipe Name {I}Cooking TimeCooking Temp.Heating Rate

R2

Batch

Batch ID {I}Amount of BatchRecipe Name {R2}Status

Temperature Ramp

Ramp ID {I}Batch ID {R4}Start TemperatureStart TimeEnd TemperatureEnd TimeStatus

R4

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Lifecycles

Build a lifecycle modelfor each class.

Lifecycle for Temperature Ramp

Do Temp. Ramp( Batch ID, End Time, End Temp )

Creating

Controlling

Complete

Start Controlling ( Ramp ID )

Temp. Ramp Complete( Ramp ID )

Ended( Ramp ID )

Timer Expired( Ramp ID )

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Actions

Specify the logic for each state’s action.


Creating


Creating

Entry/BatchID, EndTime, EndTemp >> TempRamp;CurrentTime > Self.StartTime;Self -> [R4] CookingTank.ActualTemp > Self.StartTemp;Signal Start Controlling (Ramp ID );

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Action Semantics

The action semantics should:v not over-constrain sequencing

w i.e concurrency & data flow

v separate computations fromdata accessw to make decisions about

data access without affectingalgorithm specification

v manipulate only UMLelementsw to restrict the generality

and so make aspecification language

Creating


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An Executable Model

Batch

Batch ID {I}Amount of BatchReci pe Name {R2}Status

Temperature Ramp


R4


Action for Creating


Creating

Controlling

Complete



Ended( Ramp ID )

Creating


ModelExecution

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Instances

RecipeRecipe Name

Cooking Time

Cooking Temp

Heating Rate

Nylon 23 200 2.23Kevlar 45 250 4.69Stuff 67 280 1.82

BatchBatch ID Amount of

BatchRecipe Name

Status

1 100 Nylon Filling2 127 Kevlar Emptying3 93 Nylon Filling4 123 Stuff Cooking

Recipe

Recipe Name {I}Cooking TimeCooking TemperatureHeating Rate

Batch


An executable model operateson data about instances.

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Filling

Cooking

Emptying

Create Batch( Amount of Batch, Recipe Name)

Filled( Batch ID )

Temperature Ramp Complete( Batch ID )

Emptied( Batch ID )

Batch 4

Instances

An executable model operateson instances.

Filling

Cooking

Emptying



Filled( Batch ID )

Emptied( Batch ID )

Filling

Cooking

Emptying


Filled( Batch ID )


Emptied( Batch ID )

Batch 2

Batch


Filled( Batch ID )

Emptied( Batch ID )

Filling

Cooking

Emptying


Filled( Batch ID )


Emptied( Batch ID )

Batch 1

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Execution

The lifecycle model prescribesexecution.

Filling

Cooking

Emptying


Filled( Batch ID )

Emptied( Batch ID )

Batch 2

Filled( Batch ID )

Filling

Cooking

Emptying


Filled( Batch ID )


Emptied( Batch ID )

Batch 2


BatchRecipe Name

Status



When the Temperature Ramp iscomplete, the instance moves to thenext state....and executes actions.

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Pre-existing Instances

Some instances exist before the model begins to execute...

Recipe


R2

Batch


Temperature Ramp


R4

Created during executionPre-existing

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Initialization

RecipeRecipe Name

Cooking Time

Cooking Temp

Heating Rate


Some instances exist before the model begins to execute......and so require initialization.

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Executing the Model

The model executes inresponse to signals from:v the outside,v other instances as

they executev timers

Filling

Cooking

Emptying


Filled( Batch ID )

Emptied( Batch ID )

Batch 2


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Model Database

Each schema has a corresponding database for instances.

RecipeRecipe Name

Cooking Time

Cooking Temp

Heating Rate



BatchRecipe Name

Status


Recipe


Batch


Model Schema Model Database

Capturing The Models

60


Model Repository

Capture the model in amodel repository.

FillingCooking

EmptyingWhat is thestructure of the

repository?

61


Model Structure

A meta-model defines the structureof the repository.

Attribute

Attr ID {I}Class ID {I, R12}NameType

R120..* 1

State Chart

Class ID {I, R13}Name

Class

Class ID {I}NameDescription

R131 0..1

State

Class ID {I, R14}State Number {I}Name

1

1..*

R14

62


Model Structure

A meta-model defines the structure of the repository.

State Event Matrix Entry

Class ID {I, R22}State Number {I, R22}Event ID {I, R22}New State {R23}

State


Signal Event

Event ID {I}Name

R22

R23

1..* 1..*

1

1..*

Action Group

Class ID {I, R27}State Number {I, 27}

1

1

R27

63


Model Structure

A meta-model defines the structure of the repository.

Signal Generator

Event Name {I}Supplemental Data

Data Accessor

Accessor ID {I, R13}Class NameSelector Expression

Action

Class ID {I, R34}State Number {I, R34}Action ID {I}

R34Action Group

Class ID {I}State Number {I}

Computation

Computation ID {I}Expression

1 1..*

64


Meta-Model Instances

Just like an application model,the meta-model has instances.

ClassClass ID Name Descr'n

100 Recipe .....101 Batch .....102 Temp

Ramp.....

StateClass ID State # Name

101 1 Filling101 2 Cooking101 3 Emptying102 1 ....102 2 .....102 ..... .....

Filling

Cooking

Emptying


Filled( Batch ID )


Emptied( Batch ID )

Recipe


Batch


ModelSchema

RecipeRecipe Name

Cooking Time

Cooking Temp

Heating Rate

Nylon 23 200 2.23Kevlar 45 250 4.69Stuff 67 280 1.82Batch

Batch ID Amount of Batch

Recipe Name

Status


Model Database





Ramp.....

MetaModelDatabase

State

Class ID {I, R13}State NumberName

Appl. Class


R13

MetaModelSchema

PROJECT TECHNOLOGY

Shlaer–Mellor Method n BridgePoint

INC.

ArchetypeLanguage

68


Purpose

To generate code… .





Ramp.....

MetaModelDatabase

69


Purpose

… .traverse the repository and...

Action Group State EventMatrix Entry

State Signal Event

… output text.ÊÊ

70


Example

The archetype language produces text.

.select many stateS related to instances of class->State->StateChart

where (isFinal == False)public: enum states_e { NO_STATE = 0 ,.for each state in stateS .if ( not last stateS ) ${state.Name } , .else NUM_STATES = ${state.Name} .endif.endfor};

public: enum states_e { NO_STATE = 0 , Filling , Cooking , NUM_STATES = Emptying };

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Text

To generate text:

The quick brown fox jumped over the lazy dog.

The quick brown fox jumped over the lazy dog.

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Data Access

To select any instance from the repository:

.select any class from instances of Class

Instance reference



Ramp.....

73


Substitution

To access attributes of the selected instance… .

${class.Name}



Ramp.....Batch

just text

74


Association Traversal

To traverse an association… ..

.select one StateChart related to instances of class->StateChart

State Chart


Class


R13

0..1 1Filling

Cooking

Emptying


Filled( Batch ID )

Temp. Ramp Complete( Batch ID )

Emptied( Batch ID )

Not just any one--the one that’s associated

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Arbitrary Instance

To select an arbitrary one… .

.select any state related to instances of StateChart->State

State Chart


Class


R131 0..1

1 1..*R14 State

Class ID {I, R14}State Number {I}NameisFinal

.select any state related to instances ofClass->StateChart->State

Or...

76


Complex Traversals

To qualify the selection...

State Chart


Class


R131 0..1

1 1..*R14 State

Class ID {I, R14}State Number {I}NameisFinal

.select any state related to instances of StateChart->Statewhere (isFinal == False)

77


Instance Sets

To select many instances:

.select many stateS related to instances of Class->StateChart ->State where (isFinal==False)

Filling

Cooking

Emptying


Filled( Batch ID )


Emptied( Batch ID )

StateS =

Filling

Cooking

Emptying

78


Iteration

To iterate over instances…

.select many stateS related to instances ofClass->StateChart -> State where (isFinal == False).for each state in stateS ${state.Name} ,.endfor

Filling,Cooking,Emptying,

79


Putting It Together

We may combine these techniques… .

.select many stateS related to instances of class->StateChart-> State

where (isFinal == False)public: enum states_e { NO_STATE = 0 ,.for each state in stateS .if ( not last stateS ) ${state.Name } , .else NUM_STATES = ${state.Name} .endif.endfor};

public: enum states_e { NO_STATE = 0 , Filling , Cooking , NUM_STATES = Emptying };

80


Application Semantics

An archetype language gives access toF the semantics of the applicationF as stored in the repository.

We may use the archetype language to generate code.

ADirect

Translation

82


Application Classes

Each application class becomes an implementation class.

.select many classES from instances of class

.for each class in classESclass ${class.Name} : public ActiveInstance { .invoke addPDMDecl( inst_ref class) ...};.endfor

83


Application Attributes

Each attribute becomes a private data member:

.function addPDMDecl( inst_ref class )private:

.select many attrS related to class->Attribute .for each attr in attrS ${attr.Type} {attr.Name} ; .endfor

.end function

84


State Chart Declaration

To declare a state chart:

.function addProtectedActions( inst_ref class ) .select one statechart related by class->StateChart protected: // state action member functions .select many stateS related by statechart->State .for each state in stateS .invoke addActionFunctionDecl( inst_ref state ) .endfor .end function

(i.e. all the actions in the statechart)

85


State Action Declaration

.function addActionFunctionDecl( inst_ref state )// State action: ${state.Name}static void sAsyncAction${state.Name}( stda_eventMsg_c *eventPtr, int nextState); void ${state.Name}(stda_eventMsg_c *p_evt );void asyncAction${state.Name }( );.endfor

To generate the state action declaration:

86


State Action Definition

To define the state action function… .

Signal Generator

Event Name {I}Supplemental Data

Data Accessor

Accessor ID {I, R13}Class NameSelector Expression

Action

Class ID {I, R34}State Number {I,R34}Action ID {I}

R34Action Group

Class ID {I}State Number {I}

Computation

Computation ID {I}Expression

1 1..*

… traverse the repository in the same manner.

Specifying the Architecture

88


Model the Architecture

To specify the architecture,build a model of itsconceptual entities.

ProtectedFunction Declaration

ClassDeclaration

1 0..11 1..*

ActionFunctionDeclaration

PDMDeclaration

ActionFunctionDefinition

1

1

1

1

State EnumerationDeclaration

1

1

Use the sameapproach tomodeling the

“design.”

89


Model the Architecture

To specify the architecture, build a model of itsconceptual entities.

State EventMatrix TableDeclaration

ActionPointer

Signal Event EnumerationDeclaration

R22

R23

1..* 1..*

1

1..*

Action Group

1

1

R27

90


Example Architecture

The architecture specification should bevery detailed--as well as “high-level.”

ApplicationClass Decl

Instance

0..*1

PDMDeclaration

Container

Iterator1

0..* 0..1

1

0..*

0..*

11

1..*

0..*

91


.Function addClassDeclaration

Archetypes

Build an archetype for each conceptual entity inthe architecture.

.Function addProtectedFunctionDecl


ClassDeclaration 1 0..1 1 1..*


92


Metamodel and Architecture Model

The models are similar because thearchitecture is a direct translation.


ClassDeclaration 1 0..

11 1..*


State Chart


Class


R131 0..1

State


1 1..*

R14

An Indirect Architecture

94


Description of Architecture

Because of the periodic nature of the system,we can build:v two tasks,v one of which is periodic and higher

priorityv one bit per instance to indicate presence in

the periodic statev duplicated data needed for the control

loop, andv copied over by the periodic task when

required by it

95


Description of Architecture

Periodic Task

Instance bits

Data Copy

Event-drivenTask

Eventmessage

Timer

Eventmessages

96


Application Mapping

Recipe


Batch


Temperature Ramp


Temperature RampRamp ID {I}Start TemperatureStart TimeEnd TemperatureEnd Time

Start TemperatureStart TimeEnd TemperatureEnd Time

Ramp Id Bits

Event Driven Task

Periodic Task

97


Application Mapping

Ramp Id Bits

Event Driven Task Periodic Task


Do Temp. Ramp( … )

Creating

Controlling

Complete


Ended( Ramp ID )

Controlling

98


Extended Properties

To make certain distinctions, we need to tag elementsof the meta-model.

State

Class ID {I, R14}State Number {I}NameisFinalisPeriodic

.function addPeriodicStateAction…RampIDbits[insNumber].activateActions();

System Construction

100


Recap

At this point we have:v a populated instance database for the

application describing the system to be builtv archetypes for objects in the OOA of the

architecture

What’s next?F Producing the

executable code.

101


Generating the Production Code

Invoke the archetypes and iterate over instances of thecorresponding architecture objects to generate thecomplete source code for the system.

Compile theApplication Models

Application Models Archetypes

102


Production Code

Compile the source code and include initialization datafiles (if any) to generate the deliverable production code.

Application Models

Architecture

Compile theApplication Models

Code forthe System

Libraries, Legacy orHand-written code

Run-Time Library(Mechanisms)

(Archetypes)

103


Model-Based Maintenance

To address performance-based issues:v modify the architecture models, andv and regenerate the system.

DesignChanges

Code for the System

Application Models

Architecture

F Do not modify the generated code directly.

104


Application Changes

DesignChanges

Codefor theSystem

Application Models

Architecture


To address application behavior issues,v modify the relevant application model, andv regenerate the system.


105



For subsequent product enhancements,v modify or replace the domain in question, andv regenerate the system.


Application Changes

DesignChanges

Codefor theSystem

Application Models

Architecture

106


Model Compiler

An architecture is an OOA-model compiler.

It translates a system specified in OOA into the targetprogramming language incorporating decisions made bythe architect about:v data,v control,v structures, andv time.

Architectures, likeprogramminglanguage compilers,can be bought.


108



The Shlaer-Mellor Method is a software-constructionmethod based on:

v separating systems intosubject matters (domains)

v specifying each domainwith an executable OOAmodel

v translating the models

109


Subject Matter Separation

Separation ofapplication fromarchitecture

Code

The application andarchitecture areseparate subject matters.

110


Executable UML Models

ExecutableUML models

Code

111


Executable UML Models

Executable modelscan be simulatedbefore coding begins.

Batch

Batch ID {I}Amount of BatchReci pe Name {R2}Status

Temperature Ramp


R4


Action for Creating


Creating

Controlling

Complete



Ended( Ramp ID )

Creating


112


Translation

Translation is the act ofcombining the subject

matters.

Code

Translationaccording torules

113


Translation

Translating the application domain models generates:v highly systematicv uniformv reproduciblev understandable application code

and minimizes:v coding and code inspection effortv coding errorsv component integration issues

114


Shlaer-Mellor Method

The Shlaer-Mellor Method meets the challenges ofreal-time software development by:v localizing critical software design issues to

the software architecture domainv ensuring that the design decisions are

incorporated uniformly and systematicallyv providing a framework to modify system

performance without affecting systembehavior

115


System Design: Architectures and Archetypes

This tutorial showed you how to:v identify the characteristics of the problem that

determine the system design;v engineer the system-wide design to meet

performance constraints;v model the system-wide design— the software

architecture;v build archetypes to produce efficient code.

116


System Design: Architectures and Archetypes models Code Translation according to ... “The Unified Modeling Language is a language for ... Class Diagram State Diagram

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