System models

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©Ian Sommerville 2004 Software Engineering, 7th edition Chapter 8 Slide 1

System models

Objectives

should be modelled as part of the RE process

modelling and object modelling

the Unified Modeling Language (UML)

system modelling

Topics covered

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System modelling

the functionality of the system and models are used

to communicate with customers.

perspectives

• External perspective showing the system’s context or environment;

• Behavioural perspective showing the behaviour of the system;

• Structural perspective showing the system or data architecture.

Model types

processed at different stages.

composed of other entities.

common characteristics.

reaction to events.

Context models

operational context of a system - they show what lies outside the system boundaries

affect the decision on where to position system boundaries

relationship with other systems

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The context of an ATM system

Auto-teller system

Security system

Maintenance system

Account

da tabase

Usa ge database

Branch

accounting

system

Branch

counter

system

Process models

and the processes that are supported by the system

processes and the flow of information from one process to another

Equipment procurement process

Get cost estima tes

Accept deli very of equipment

Check deliver ed items Valida te

specifica tion

Specify

equipment

requir ed

Choose equipmentPlace

order Install equipment Find

suppliers

Supplier

da tabase

Accept deli ver ed equipment

Equipment

da tabase

Equipment

spec.

Checked

spec.

Delivery note Delivery note

Order notifica tion

Installa tion

Installa tion acceptance

Equipment details

Check ed and signed or der f orm

Order details plus blank or der for m

Spec + supplier + estima te Supplier list

Equipment

spec.

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Behavioural models

overall behaviour of a system

processed as it moves through the system;

response to events.

so both of them are required to describe the system’s behaviour

Data-processing models

model the system’s data processing

flows through a system

methods

can understand

Order processing DFD

Complete

or der f orm

Or der

details +

blank

or der f orm

Valida te order Recor d

or der

Send to supplier

Adjust availab le budget

Budget file

Or ders file

Completed

order f or m

Signed order f or m Signed order f orm

Check ed and signed or der + or der notifica tion

Or der amount + account details

Signed order f orm Order details

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Data flow diagrams

perspective

associated with a process is helpful to develop an overall understanding of the system

showing the data exchange between a system and other systems in its environment

Insulin pump DFD

Insulin requir ement computa tion

Blood sugar anal ysis Blood sugar

sensor

Insulin deli very contr oller Insulin

pump

Blood

par ameters

Blood sugar level

Insulin

Pump contr ol

requir ement

State machine models

response to external and internal events.

often used for modelling real-time systems.

and events as arcs between these nodes When an event occurs, the system moves from one state to another.

used to represent state machine models.

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Statecharts

sub-models (see following slide)

following the ‘do’ in each state

the states and the stimuli

Microwave oven model

Full po wer

Enabled

do: operate oven

Full

po w er

Half

po wer

Half

po wer

Full

po wer

Number

Door Door closed

Door closed

Door Start

do: set power

= 600

Half po wer

do: set power

= 3 00

Set time do: get number exit: set time

Disab led

Operation

Cancel

Waiting do: display time

Waiting

do: display

time

do: display 'Ready'

do: display 'Waiting'

Timer

Microwave oven state description

Waiting The oven is waiting for input The display shows the current time.

Half power The oven power is set to 300 watts The display shows ŌHalf powerÕ.

Full power The oven power is set to 600 watts The display shows ŌFull powerÕ.

Set time The cooking time is s et to the userÕs input value The display shows the cooking time selected and is updated as the time is set.

Disabled Oven operation is disabled for safety Interior oven light is on Display shows ŌNot readyÕ.

Enabled Oven operation is enabled Interior oven light is off Display shows ŌReady to cookÕ Operation Oven in operation Interior oven light is on Display shows the timer countdown On shows ŌCooking completeÕ while buzzer is sounding.

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Microwave oven stimuli

Half power The user has pressed the half power button

Full power The user has pressed the full power button

Timer The user has pressed one of the timer buttons

Number The user has pressed a numeric key

Door open The oven door switch is not closed

Door closed The oven door switch is closed

Start The user has pressed the start button

Cancel The user has pressed the cancel button

Microwave oven operation

Cook do: run generator

Done do: buzzer on for 5 secs.

Waiting

Alarm

do: display

event

do: check

status

Checking

Turntable

fault

Emitter fault

Disabled

OK

Timeout Time

Door open Cancel Operation

Semantic data models

processed by the system.

entities in the system, the relationships between these entities and the entity attributes

implemented using relational databases.

and associations can be used.

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Library semantic model

Source title publisher issue date pages 1

Article

title

authors

pdf file

fee

has-links 1

Buyer

name

address

e-mail

billing info

places

fee-payable-to

n

1

n

published-in

1

1 1 Copyright

Agency name address

Country copyright form tax rate

1 Order

order number

date

tax status

in 1

Data dictionaries

the system models Descriptions of the entities, relationships and attributes are also included.

• Support name management and avoid duplication;

• Store of organisational knowledge linking analysis, design and implementation;

Data dictionary entries

Article Details of the published article that may be ordered bypeople using LIBSYS. Entity 30.12.2002

authors The names of the authors of the article who may be due

Buyer The person or organisation that orders a co py of the

fee-payable-to

A 1:1 relationship between Article and the Copyright

Agency who should be paid the copyright fee. Relation 29.12.2002

Address

(Buyer)

The address of the buyer This is used to any paper

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Object models

object classes and their associations.

objects with common attributes and the services (operations) provided by each object.

• Inheritance models;

• Aggregation models;

• Interaction models.

Object models

entities manipulated by the system

model using this approach

difficult process requiring a deep

understanding of the application domain

reusable across systems

Inheritance models

common features of all classes.

from one or more super-classes these may then be specialised as necessary.

duplication in different branches is to be avoided.

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Object models and the UML

the developers of widely used object-oriented analysis and design methods.

object-oriented modelling.

• Object classes are rectangles with the name at the top, attributes in the middle section and operations in the bottom section;

• Relationships between object classes (known as associations) are shown as lines linking objects;

• Inheritance is referred to as generalisation and is shown

‘upwards’ rather than ‘downwards’ in a hierarchy.

Library class hierarchy

Catalo gue n umber Acquisition da te Cost Type Status Number of copies Library item

Acquire () Catalo gue () Dispose () Issue () Return ()

Author

Edition

Pub lication da te

ISBN

Book

Year

Issue

Ma gazine Dir ector

Da te of release Distrib utor Film Version Pla tfor m

Computer pro gram

Title

Pub lisher

Pub lished item

Title Medium Recor ded item

User class hierarchy

Name Address Phone Reg istration # Library user

Reg ister () De-reg ister ()

Affiliation

Reader

Items on loan Max loans Borrower

Depar tment Depar tment phone Staff Major subject Home ad dress Student

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Multiple inheritance

from a single parent class, a system which supports multiple inheritance allows object classes to inherit from several super-classes.

attributes/services with the same name in different super-classes have different semantics.

reorganisation more complex.

Multiple inheritance

# Tapes Talking book

Author

Edition

Pub lication da te

ISBN

Book

Speak er Duration Recor ding da te Voice recording

Object aggregation

that are collections are composed of other classes

relationship in semantic data models

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Object aggregation

Videota pe Tape ids Lectur e notes Text OHP slides Slides Assignment

Credits

Solutions

Text

Diag rams

Exercises

#Pr ob lems

Description

Course title Number Year Instructor Study pack

Object behaviour modelling

between objects to produce some particular system behaviour that is specified as a use-case

diagrams) in the UML are used to model interaction between objects

Issue of electronic items

:Library User

Ecat:

Catalog

Lookup

Issue

Display

:Library Item Lib1:NetServer

Issue licence Accept licence

Compress

Deliver

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Structured methods

modelling as an inherent part of the method

for deriving these models and rules and guidelines that should apply to the models

part of a structured method

Method weaknesses

requirements

about whether a method is appropriate for a given problem

detailed and difficult for users to understand

CASE workbenches

support related software process activities such as analysis, design or testing

system modelling during both requirements engineering and system design

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

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An analysis and design workbench

Centr al infor ma tion repository Code

gener ator

Query langua ge facilities

Structur ed diag ramming tools

Da ta

dictionary

Repor t gener ation facilities

Design, anal ysis and checking tools Forms

cr ea tion

tools

Impor t/e xpor t facilities

Analysis workbench components

Key points

Complementary types of model provide different system information

system in its environment with other systems and processes

data processing in a system

behaviour in response to internal or external events

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Key points

structure of data which is imported to or exported by the systems

entities, their classification and aggregation

between actors and the system objects that they use

developing system models

Tiêu đề	System models
Tác giả	Ian Sommerville
Trường học	University of Stirling
Chuyên ngành	Software Engineering
Thể loại	Thesis
Năm xuất bản	2004
Thành phố	Stirling

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Số trang	15
Dung lượng	131,21 KB