System models zAbstract descriptions of systems …spiros/teaching/CS451/pdf/... · ·...
Transcript of System models zAbstract descriptions of systems …spiros/teaching/CS451/pdf/... · ·...
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 1
System models
Abstract descriptions of systems whose requirements are being analysed
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 2
System modellingSystem modelling helps the analyst to understand the functionality of the system and models are used to communicate with customersDifferent models present the system from different 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
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 3
Structured methodsStructured methods incorporate system modelling as an inherent part of the methodMethods define a set of models, a process for deriving these models and rules and guidelines that should apply to the modelsCASE tools support system modelling as part of a structured method
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 4
Method weaknessesThey do not model non-functional system requirementsThey do not usually include information about whether a method is appropriate for a given problemThey may produce too much documentationThe system models are sometimes too detailed and difficult for users to understand
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 5
Model typesData processing model showing how the data is processed at different stagesComposition model showing how entities are composed of other entitiesArchitectural model showing principal sub-systemsClassification model showing how entities have common characteristicsStimulus/response model showing the system’s reaction to events
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 6
Context modelsContext models are used to illustrate the boundaries of a systemSocial and organisational concerns may affect the decision on where to position system boundariesArchitectural models show the a system and its relationship with other systems
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 7
The context of an ATM system
Auto-tellersystem
Securitysystem
Maintenancesystem
Accountdatabase
Usagedatabase
Branchaccounting
system
Branchcountersystem
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 8
Process modelsProcess models show the overall process and the processes that are supported by the systemData flow models may be used to show the processes and the flow of information from one process to another
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 9
Equipment procurement process
Get costestimates
Acceptdelivery ofequipment
Checkdelivered
items
Validatespecification
Specifyequipmentrequired
Choosesupplier
Placeequipment
order
Installequipment
Findsuppliers
Supplierdatabase
Acceptdelivered
equipment
Equipmentdatabase
Equipmentspec.
Checkedspec.
Deliverynote
Deliverynote
Ordernotification
Installationinstructions
Installationacceptance
Equipmentdetails
Checked andsigned order form
Orderdetails +
Blank orderform
Spec. +supplier +estimate
Supplier listEquipment
spec.
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 10
Behavioural modelsBehavioural models are used to describe the overall behaviour of a systemTwo types of behavioural model are shown here– Data processing models that show how data is processed as it
moves through the system– State machine models that show the systems response to events
Both of these models are required for a description of the system’s behaviour
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 11
Data-processing modelsData flow diagrams are used to model the system’s data processingThese show the processing steps as data flows through a systemIntrinsic part of many analysis methodsSimple and intuitive notation that customers can understandShow end-to-end processing of data
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 12
Order processing DFD
Completeorder form
Orderdetails +
blankorder form
Validateorder
Recordorder
Send tosupplier
Adjustavailablebudget
Budgetfile
Ordersfile
Completedorder form
Signedorder form
Signedorder form
Checked andsigned order
+ ordernotification
Orderamount
+ accountdetails
Signedorder form
Orderdetails
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 13
Data flow diagramsDFDs model the system from a functional perspectiveTracking and documenting how the data associated with a process is helpful to develop an overall understanding of the systemData flow diagrams may also be used in showing the data exchange between a system and other systems in its environment
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 14
CASE toolset DFD
Designeditor
Designcross checker
Designanalyser
Reportgenerator
Designdatabase
Code skeletongenerator
Designdatabase
Inputdesign
Validdesign
Checkeddesign
Designanalysis
Userreport
and
Referenceddesigns
Checkeddesign Output
code
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 15
State machine modelsThese model the behaviour of the system in response to external and internal eventsThey show the system’s responses to stimuli so are often used for modelling real-time systemsState machine models show system states as nodes and events as arcs between these nodes. When an event occurs, the system moves from one state to anotherStatecharts are an integral part of the UML
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 16
Microwave oven modelFull power
Enabled
do: operateoven
Fullpower
Halfpower
Halfpower
Fullpower
Number
TimerDooropen
Doorclosed
Doorclosed
Dooropen
Start
do: set power = 600
Half powerdo: set power = 300
Set time
do: get numberexit: set time
Disabled
Operation
Timer
Cancel
Waiting
do: display time
Waiting
do: display time
do: display 'Ready'
do: display 'Waiting'
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 17
Microwave oven state descriptionState 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 ‘Half
power’.Full power The oven power is set to 600 watts. The display shows ‘Full
power’.Set time The cooking time is set to the user’s 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 ‘Not ready’.Enabled Oven operation is enabled. Interior oven light is off. Display
shows ‘Ready to cook’.Operation Oven in operation. Interior oven light is on. Display shows the
timer countdown. On completion of cooking, the buzzer issounded for 5 seconds. Oven light is on. Display shows ‘Cookingcomplete’ while buzzer is sounding.
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 18
Microwave oven stimuliStimulus Description
Half power The user has pressed the half power buttonFull power The user has pressed the full power buttonTimer The user has pressed one of the timer buttonsNumber The user has pressed a numeric keyDoor open The oven door switch is not closedDoor closed The oven door switch is closedStart The user has pressed the start buttonCancel The user has pressed the cancel button
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 19
StatechartsAllow the decomposition of a model into sub-models (see following slide)A brief description of the actions is included following the ‘do’ in each stateCan be complemented by tables describing the states and the stimuli
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 20
Microwave oven operation
Cookdo: run generator
Done
do: buzzer on for 5 secs.
Waiting
Alarm
do: display event
do: checkstatus
Checking
Turntablefault
Emitterfault
Disabled
OK
Timeout
TimeOperation
Dooropen Cancel
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 21
Semantic data modelsUsed to describe the logical structure of data processed by the systemEntity-relation-attribute model sets out the entities in the system, the relationships between these entities and the entity attributesWidely used in database design. Can readily be implemented using relational databasesNo specific notation provided in the UML but objects and associations can be used
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 22
Software design semantic modelDesign
namedescriptionC-dateM-date
Link
nametype
Node
nametype
links
has-links
12
1 n
Label
nametexticon
has-labelshas-labels
1
n
1
n
has-linkshas-nodes is-a
1
n
1
n1
1
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 23
Object modelsObject models describe the system in terms of object classesAn object class is an abstraction over a set of objects with common attributes and the services (operations) provided by each objectVarious object models may be produced– Inheritance models– Aggregation models– Interaction models
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 24
Object modelsNatural ways of reflecting the real-world entities manipulated by the systemMore abstract entities are more difficult to model using this approachObject class identification is recognised as a difficult process requiring a deep understanding of the application domainObject classes reflecting domain entities are reusable across systems
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 25
Inheritance modelsOrganise 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. these may then be specialised as necessaryClass hierarchy design is a difficult process if duplication in different branches is to be avoided
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 26
The Unified Modeling LanguageDevised by the developers of widely used object-oriented analysis and design methodsHas become an effective standard for object-oriented modellingNotation– 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 hierarchyCatalogue numberAcquisition dateCostTypeStatusNumber of copies
Library item
Acquire ()Catalogue ()Dispose ()Issue ()Return ()
AuthorEditionPublication dateISBN
Book
YearIssue
Magazine
DirectorDate of releaseDistributor
Film
VersionPlatform
Computerprogram
TitlePublisher
Published item
TitleMedium
Recorded item
User class hierarchyNameAddressPhoneRegistration #
Library user
Register ()De-register ()
Affiliation
Reader
Items on loanMax. loans
Borrower
DepartmentDepartment phone
Staff
Major subjectHome address
Student
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 29
Multiple inheritanceRather than inheriting the attributes and services from a single parent class, a system which supports multiple inheritance allows object classes to inherit from several super-classesCan lead to semantic conflicts where attributes/services with the same name in different super-classes have different semanticsMakes class hierarchy reorganisation more complex
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 30
Multiple inheritance
# Tapes
Talking book
AuthorEditionPublication dateISBN
Book
SpeakerDurationRecording date
Voice recording
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 31
Object aggregationAggregation model shows how classes which are collections are composed of other classesSimilar to the part-of relationship in semantic data models
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 32
Object aggregation
Videotape
Tape ids.
Lecturenotes
Text
OHP slides
Slides
Assignment
Credits
Solutions
TextDiagrams
Exercises
#Problems Description
Course titleNumberYearInstructor
Study pack
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 33
Object behaviour modellingA behavioural model shows the interactions between objects to produce some particular system behaviour that is specified as a use-caseSequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 34
Issue of electronic items
:Library User
Ecat:Catalog
Lookup
Issue
Display
:Library Item Lib1:NetServer
Issue licence
Accept licence
Compress
Deliver
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 35
CASE workbenchesA coherent set of tools that is designed to support related software process activities such as analysis, design or testingAnalysis and design workbenches support system modelling during both requirements engineering and system designThese workbenches may support a specific design method or may provide support for a creating several different types of system model
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 36
An analysis and design workbench
Centralinformationrepository
Codegenerator
Querylanguagefacilities
Structureddiagramming
tools
Datadictionary
Reportgenerationfacilities
Design, analysisand checking
tools
Formscreation
tools
Import/exportfacilities
©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 37
Analysis workbench componentsDiagram editorsModel analysis and checking toolsRepository and associated query languageData dictionaryReport definition and generation toolsForms definition toolsImport/export translatorsCode generation tools