CSC 205: Software Engineering I

© 2000 Franz Kurfess System Design Methods 1

CSC 205: Software Engineering ICSC 205: Software Engineering I

Dr. Franz J. Kurfess

Computer Science Department

Cal Poly


Course OverviewCourse Overview Introduction Requirements Engineering

Requirements Elicitation Requirements Management

Project Management System Design Methods

and Notations

Design Models and Object-Oriented Design

Design Analysis and Formal Specification

Design Analysis and Verification

Conclusions


Chapter OverviewSystem Design Methods and Notations

Chapter OverviewSystem Design Methods and Notations Motivation Objectives Context Models Behavioral Models Data Models Object Models

CASE workbenches Important Concepts and

Terms Chapter Summary


LogisticsLogistics

Midterm Friday, February 16

Project Presentations probably Friday, Feb. 9 with Lori Fisher


MotivationMotivation

it is helpful to consider a system from different perspectives in order to get a better understanding

various methods concentrate on specific aspects components functions data flow data structures

tools affiliated with these methods help with the capturing of system information


Objectives

to explain why the context of a system should be modeled as part of the re process

to describe behavioral modeling, data modeling and object modeling

to introduce some of the notations used in the Unified Modeling Language (UML)

to show how CASE workbenches support system modeling

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System ModelsSystem Models

abstract descriptions of systems whose requirements are being analyzed


System Modeling

helps the analyst to understand the functionality of the system

models can be used to communicate with customersdifferent models present the system from different

perspectives external perspective

the system’s context or environment

behavioral perspective the behavior of the system

structural perspective the system or data architecture

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Structured MethodsStructured Methods

incorporate system modeling as an inherent part of the method

these methods define a set of models a process for deriving these models and rules guidelines that should apply to the models

CASE tools support system modeling as part of a structured method

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Structured Method WeaknessesStructured Method Weaknesses

do not model non-functional system requirementsdo not usually include information about whether a

method is appropriate for a given problemmay produce too much documentationthe system models are sometimes too detailed and

difficult for users to understand

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Model TypesModel Types

data processing model how the data is processed at different stages

composition model how entities are composed of other entities

architectural model principal sub-systems

classification model entities with common characteristics

stimulus/response model the system’s reaction to external or internal events


Context ModelsContext Models

used to illustrate the boundaries of a systemsocial and organizational concerns may affect the

decision on where to position system boundariesarchitectural models

show the system and its relationship with other systems

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ATM System Context ATM System Context

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AutomatedTeller

SecuritySystem

AccountData Base

UsageData Base

MaintenanceSystem

Branch CounterSystem

Branch Accounting

System


Process ModelsProcess Models

show the overall process and the processes that are supported by the system

data flow models may be used to show the processes and the flow of

information from one process to another

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Equipment Procurement Process

Get costestimatesAcceptdelivery ofequipment CheckdelivereditemsValidatespecificationSpecifyequipmentrequired Choosesupplier Placeequipmentorder InstallequipmentFindsuppliersSupplierdatabase AcceptdeliveredequipmentEquipmentdatabase

Equipmentspec. Checkedspec. DeliverynoteDeliverynoteOrdernotification InstallationinstructionsInstallationacceptanceEquipmentdetailsChecked andsigned order form

Orderdetails +Blank orderformSpec. +supplier +estimateSupplier listEquipmentspec.

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Behavioral ModelsBehavioral Models

behavioral models are used to describe the overall behavior of a system

two types of behavioral model are shown here data processing models

show how data is processed as it moves through the system

state machine models show how the system responds to events

both of these models are required for a description of the system’s behavior

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Data-processing Models

data flow diagrams used to model the system’s data processing show the processing steps as data flows through a system intrinsic part of many analysis methods simple and intuitive notation that customers can

understand show end-to-end processing of data

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Order Processing DFD

Completeorder formOrderdetails +blankorder form ValidateorderRecordorderSend tosupplierAdjustavailablebudgetBudgetfileOrdersfileCompletedorder formSignedorder formSignedorder formChecked andsigned order+ ordernotificationOrderamount+ accountdetailsSignedorder formOrderdetails

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slightly different notation from examples in the previous chapter [FJK]


Data Flow DiagramsData Flow Diagrams

DFDs model the system from a functional perspective

tracking and documenting how the data associated with a process is helpful to develop an overall understanding of the system

data flow diagrams may also be used in showing the data exchange between a system and other systems in its environment

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CASE Toolset DFD

Designeditor Designcross checkerDesignanalyserReportgeneratorDesigndatabase Code skeletongenerator DesigndatabaseInputdesignValiddesignCheckeddesignDesignanalysisUserreportandReferenceddesignsCheckeddesign Outputcode

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State Machine ModelsState Machine Models

model the behavior of the system in response to external and internal events

show the system’s responses to stimuli often used for modeling real-time systems

notation system states as nodes events as arcs between these nodes

when an event occurs, the system moves from one state to another

state charts are an integral part of the UML

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Microwave Oven ModelMicrowave Oven ModelFull powerEnableddo: operateoven

FullpowerHalfpower HalfpowerFullpower NumberTimerDooropenDoorclosedDoorclosed DooropenStart

do: set power = 600Half powerdo: set power = 300

Set timedo: get numberexit: set timeDisabled

OperationTimerCancelWaitingdo: display time

Waitingdo: display timedo: display 'Ready'do: display 'Waiting'

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Microwave Oven State DescriptionMicrowave Oven State Description

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Microwave Oven StimuliMicrowave Oven Stimuli

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State ChartsState Charts

allow the decomposition of a model into sub-modelsa brief description of the actions is included

following the ‘do’ in each state

can be complemented by tables describing the states and the stimuli

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Microwave Oven OperationMicrowave Oven Operation

Cookdo: run generatorDonedo: buzzer on for 5 secs.WaitingAlarmdo: display eventdo: checkstatusCheckingTurntablefaultEmitterfaultDisabled

OKTimeoutTimeOperationDooropen Cancel

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Semantic Data Models

describe the logical structure of data processed by the system

entity-relation-attribute model entities in the system relationships between these entities entity attributes

widely used in database design can readily be implemented using relational databases

no specific notation provided in the UML objects and associations can be used

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Software Design Semantic ModelDesignnamedescriptionC-dateM-dateLinknametypeNodenametype linkshas-links121 n

Labelnametexticon has-labelshas-labels 1n1nhas-linkshas-nodesis-a1n

1n11

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Data DictionariesData Dictionaries

lists of all of the names used in the system models also includes descriptions of the entities, relationships and

attributes

advantages support name management and avoid duplication store of organizational knowledge linking analysis, design

and implementation

many CASE workbenches support data dictionaries

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Data Dictionary EntriesData Dictionary Entries

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Object Models

describe the system in terms of object classesan object class is an abstraction over a set of objects

common attributes services (operations) provided by each object

various object models may be produced inheritance models aggregation models interaction models

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Object Models

natural ways of reflecting the real-world entities manipulated by the system

more abstract entities are more difficult to modelobject class identification is a difficult process

requires a deep understanding of the application domain

object classes reflecting domain entities may be reusable across systems

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Inheritance Models

organize the domain object classes into a hierarchyclasses at the top of the hierarchy reflect the

common features of all classesobject classes inherit their attributes and services

from one or more super-classes may then be specialized as necessary

class hierarchy design is a difficult process duplication in different branches should be avoided

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The Unified Modeling LanguageThe Unified Modeling Language

devised by the developers of widely used object-oriented analysis and design methods the “three amigos” Booch, Jacobson, Rumbaugh

has become an effective standard for object-oriented modeling

can be used at different levels of abstraction conceptual level specification level implementation level

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UML ModelsUML Models

functional model use case diagrams

object model class diagram objects, attributes, associations, operations

dynamic model sequence diagrams state chart diagrams activity diagrams


UML NotationUML Notation

object classes rectangles with the name at the top, attributes in the

middle section and operations in the bottom section

associations relationships between object classes shown as lines linking objects

inheritance is referred to as generalization shown ‘upwards’ rather than ‘downwards’ in a hierarchy

Library Class

Hierarchy

Catalogue numberAcquisition dateCostTypeStatusNumber of copiesLibrary itemAcquire ()Catalogue ()Dispose ()Issue ()Return ()AuthorEditionPublication dateISBNBookYearIssueMagazineDirectorDate of releaseDistributorFilmVersionPlatformComputerprogramTitlePublisherPublished itemTitleMediumRecorded item

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NameAddressPhoneRegistration #Library userRegister ()De-register ()AffiliationReader Items on loanMax. loansBorrowerDepartmentDepartment phoneStaffMajor subjectHome addressStudent[Sommerville 01]

User Class HierarchyUser Class Hierarchy


Multiple Inheritance

allows object classes to inherit from several super-classes rather than inheriting the attributes and services from a

single parent class

can lead to semantic conflicts attributes/services with the same name in different super-

classes have different semantics

can simplify specifications of objects substantiallymay make class hierarchy reorganization more

complex

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Multiple Inheritance

# TapesTalking bookAuthorEditionPublication dateISBNBookSpeakerDurationRecording dateVoice recording

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Object Aggregation

aggregation model shows how classes which are collections are composed of

other classes similar to the part-of relationship in semantic data models

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Object Aggregation

VideotapeTape ids.LecturenotesTextOHP slidesSlidesAssignmentCreditsSolutionsTextDiagramsExercises#Problems Description

Course titleNumberYearInstructorStudy pack

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Object Behavior ModelingObject Behavior Modeling

behavioral model shows the interactions between objects to produce some

particular system behavior that is specified as a use-case

sequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects

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Issue of Electronic ItemsIssue of Electronic Items

:Library UserEcat:CatalogLookupIssueDisplay:Library ItemLib1:NetServer

Issue licenceAccept licence CompressDeliver[Sommerville 01]


CASE WorkbenchesCASE Workbenches

coherent set of tools designed to support related software process activities such as analysis, design or testing

analysis and design workbenches support system modeling during both requirements

engineering and system design

these workbenches may support a specific design method or may provide support for a creating several different types of system model

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An Analysis and Design Workbench

CentralinformationrepositoryCodegenerator QuerylanguagefacilitiesStructureddiagrammingtoolsDatadictionary ReportgenerationfacilitiesDesign, analysisand checkingtoolsFormscreationtools Import/exportfacilities

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Analysis Workbench Components

diagram editorsmodel analysis and checking toolsrepository and associated query languagedata dictionaryreport definition and generation toolsforms definition toolsimport/export translatorscode generation tools

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Important Concepts and TermsImportant Concepts and Terms inheritance model interaction model multiple inheritance object object class object model process model requirements sequence diagram stimulus-response model state chart/diagram state machine model system model Unified Modeling Language (UML) use case diagram

activity diagram aggregation model architectural model association behavioral model CASE workbench classification model component composition model context model data dictionary data flow data flow diagram data model data structure entity-relation-attribute model entity-relationship diagram


Chapter SummaryChapter Summary


Chapter Summary

a model is an abstract system view complementary types of model provide different system

informationcontext models show the position of a system in its

environment together with other systems and processes

data flow models may be used to model the data processing in a system

state machine models describe the system’s behavior in response to internal or external events

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Chapter Summary (cont.)

semantic data models describe the logical structure of data items

object models describe the logical system entities and their classification and aggregation

CASE workbenches support the development of system models

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CSC 205: Software Engineering I

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