SYSTEM MODELS MUHAMMAD RIZWAN. Objectives To explain why the context of a system should be modelled...

SYSTEM MODELS

MUHAMMAD RIZWAN

Objectives

To explain why the context of a system should be modelled as part of the RE process

To describe behavioural modelling, data modelling and object modelling

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

To show how CASE workbenches support system modelling

Topics covered

Context models Behavioural models Data models Object models CASE workbenches

System modelling

System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers.

Different 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.

Model types

Data processing model showing how the data is processed at different stages.

Composition model showing how entities are composed of other entities.

Architectural model showing principal sub-systems.

Classification model showing how entities have common characteristics.

Stimulus/response model showing the system’s reaction to events.

Context models

Context models are used to illustrate the operational context of a system - they show what lies outside the system boundaries.

Social and organisational concerns may affect the decision on where to position system boundaries.

Architectural models show the system and its relationship with other systems.

The context of an ATM system

Auto-tellersystem

Securitysystem

Maintenancesystem

Accountdatabase

Usagedatabase

Branchaccounting

system

Branchcountersystem

Process models

Process 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.

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 plusblank order

form

Spec. +supplier +estimate

Supplier listEquipment

spec.

Behavioural models

Behavioural models are used to describe the overall behaviour of a system.

Two types of behavioural model are: 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. These models show different perspectives

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

Data-processing models

Data flow diagrams (DFDs) may be used to model the system’s data processing.

These show the processing steps as data flows through a system.

DFDs are an intrinsic part of many analysis methods.

Simple and intuitive notation that customers can understand.

Show end-to-end processing of data.

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

Data 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.

Data Flow Diagram

Squares representing external entities, which are sources or destinations of data.

Rounded rectangles representing processes, which take data as input, do something to it, and output it.

Arrows representing the data flows, which can either be electronic data or physical items.

Open-ended rectangles representing data stores, including electronic stores such as databases or XML files and physical stores such as or filing cabinets or stacks of paper.

Creating Data Flow Diagrams

Steps:

1. Create a list of activities

2. Construct Context Level DFD(identifies external entities and processes)

3. Construct Level 0 DFD (identifies manageable sub process )

4. Construct Level 1- n DFD (identifies actual data flows and data stores )

5. Check against rules of DFD

DFD Naming Guidelines

External Entity Noun Data Flow Names of data Process verb phrase

a system name a subsystem name

Data Store Noun


Lemonade Stand Example


Steps:


• Old way: no Use-Case Diagram

• New way: use Use-Case Diagram

2. Construct Context Level DFD(identifies sources and sink)

3. Construct Level 0 DFD (identifies manageable sub processes )


Example

The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams.


1. Create a list of activitiesExample

Think through the activities that take place at a lemonade stand.

Customer OrderServe ProductCollect PaymentProduce ProductStore Product


Example

Also think of the additional activities needed to support the basic activities.

Customer OrderServe ProductCollect PaymentProduce ProductStore ProductOrder Raw MaterialsPay for Raw MaterialsPay for Labor



Example

Group these activities in some logical fashion, possibly functional areas.

Customer OrderServe ProductCollect Payment

Produce ProductStore Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor



0.0Lemonade

SystemEMPLOYEECUSTOMER

PayPayment

Order

Context Level DFD

Example

Create a context level diagram identifying the sources and sinks (users).




Pay for Labor

VENDOR

PaymentPurchase Order

Production Schedule

Received GoodsTime Worked

Sales Forecast

2. Construct Context Level DFD(identifies sources and sink)

Product Served


Level 0 DFD

Example

Create a level 0 diagram identifying the logical subsystems that may exist.




Pay for Labor

3. Construct Level 0 DFD (identifies manageable sub processes )

2.0Production EMPLOYEEProduction

Schedule

1.0Sale

3.0Procure-

ment

Sales Forecast

Product Ordered

CUSTOMER

Pay

Payment

Customer Order

VENDOR

Payment

Purchase Order Order Decisions

Received Goods

Time Worked

Inventory

Product Served

4.0Payroll


Level 1 DFD

Example

Create a level 1 decomposing the processes in level 0 and identifying data stores.


1.3Produce

Sales Forecast Sales ForecastPayment




Pay for Labor

1.1Record Order

Customer Order

ORDER

1.2Receive Payment

PAYMENT

Severed Order

Request for Forecast

CUSTOMER


Level 1 DFD

Example


4. Construct Level 1 (continued)




Pay for Labor

2.1Serve

Product

Product Order

ORDER

2.2Produce Product

INVENTORTY

Quantity Severed

Production Schedule

RAW MATERIALS

2.3Store

Product

Quantity Produced & Location Stored

Quantity Used

Production Data


Level 1 DFD

Example






Pay for Labor

3.1Produce Purchase

Order

Order DecisionPURCHASE

ORDER

3.2Receive

Items

Received Goods

RAW MATERIALS

3.3Pay

Vendor

Quantity Received

Quantity On-Hand

RECEIVED ITEMS

VENDOR

Payment Approval

Payment


Level 1 DFD

Example



Time Worked




Pay for Labor

4.1Record Time

Worked

TIME CARDS

4.2Calculate

Payroll

Payroll Request

EMPLOYEE

4.3Pay

Employee

Employee ID

PAYROLL

PAYMENTS

Payment Approval

Payment

Unpaid time cards

Process Decomposition

4.1Record Time

Worked

4.2Calculate

Payroll

4.3Pay

Employee

3.1Produce Purchase

Order

3.2Receive

Items

3.3Pay

Vendor

2.1Serve

Product

2.2Produce Product

2.3Store

Product

1.1Record Order

1.2Receive Payment

2.0Production

1.0Sale

3.0Procure-

ment

4.0Payroll

0.0Lemonade

System

Level 0 Level 1Context Level

DFD Example: Bus Garage Repairs

Buses come to a garage for repairs. A mechanic and helper perform the repair,

record the reason for the repair and record the total cost of all parts used on a Shop Repair Order.

Information on labor, parts and repair outcome is used for billing by the Accounting Department, parts monitoring by the inventory management computer system and a performance review by the supervisor.

DFD Example: Bus Garage Repairs (cont’d) External Entities: Bus, Mechanic, Helper,

Supervisor, Inventory Management System, Accounting Department, etc.

Key process (“the system”): performing repairs and storing information related to repairs

Processes: Record Bus ID and reason for repair Determine parts needed Perform repair Calculate parts extended and total cost Record labor hours, cost

DFD Example: Bus Garage Repairs (cont’d) Data stores:

Personnel file Repairs file Bus master list Parts list

Data flows: Repair order Bus record Parts record Employee timecard Invoices

Bus

Mechanic

Helper Bus Repair ProcessSystem

Supervisor

Accounting

Bus Garage Context Diagram

Mechanical problem to be repaired

Labor

Labor

Fixed mechanical problems

Inventory Managemen

t System

Repair summary

List of parts used

Labor, parts cost details

CSUB Burger’s Order Processing System

Draw the CSUB Burger’s context diagram System

Order processing system

External entities Kitchen Restaurant Customer

Processes Customer order Receipt Food order Management report

Example Ref by Yong Choi BPA CSUB

Insulin pump DFD

Insulinrequirementcomputation

Blood sugaranalysis

Blood sugarsensor

Insulindelivery

controller

Insulinpump

Blood

Bloodparameters

Blood sugarlevel

Insulin

Pump controlcommands Insulin

requirement

Event-driven Modeling (State machine models) These model the behaviour of the system in

response to external and internal events. They show the system’s responses to stimuli so

are often used for modelling real-time systems. State 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 another.

State charts are an integral part of the UML and are used to represent state machine models.

Statecharts

Allow the decomposition of a model into sub-models (see following slide).

In UML, state diagrams rounded rectangles represent system states.

A brief description of the actions is included following the ‘do’ in each state.

The labeled arrows represent stimuli that force action from one state to another

Start & end state are represented by filled circle.

Microwave oven model

Microwave oven state description

Microwave oven stimuli

Microwave oven operation

Cookdo: run

generator

Done

do: buzzer onfor 5 secs.

Waiting

Alarm

do: displayevent

do: checkstatus

Checking

Turntablefault

Emitterfault

Disabled

OK

Timeout

Time

Door open Cancel

Operation

Semantic (Structural) data models Used to describe the logical structure of data

processed by the system. An entity-relation-attribute model sets out the

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

Widely used in database design. Can readily be implemented using relational databases.

No specific notation provided in the UML but objects and associations can be used.

Library semantic model

Source

titlepublisherissuedatepages

1

Article

titleauthorspdf filefee

has-links

1

Buyer

nameaddresse-mailbilling info

places

fee-payable-to

n

1

n

published-in

delivers in

m n

1

1

1

CopyrightAgencynameaddress

Country

copyright formtax rate

1

Order

order numbertotal paymentdatetax status

in

1

Data dictionaries

Data dictionaries are lists of all of the names used in the system models. Descriptions of the entities, relationships and attributes are also included.

Advantages Support name management and avoid duplication; Store of organisational knowledge linking analysis,

design and implementation; Many CASE workbenches support data

dictionaries.

Data dictionary entries

Object models

Object models describe the system in terms of object classes and their associations.

An object class is an abstraction over a set of objects with common attributes and the services (operations) provided by each object.

Various object models may be produced Inheritance models; Aggregation models; Interaction models.

Object models

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

More abstract entities are more difficult to model using this approach

Object class identification is recognised as a difficult process requiring a deep understanding of the application domain

Inheritance models

Organise the domain object classes into a hierarchy.

Classes at the top of the hierarchy reflect the common features of all classes.

Object classes inherit their attributes and services from one or more super-classes. these may then be specialised as necessary.

Class hierarchy design can be a difficult process if duplication in different branches is to be avoided.

Object models and the UML

The UML is a standard representation devised by the developers of widely used object-oriented analysis and design methods.

It has become an effective standard for object-oriented modelling.

Notation 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

Catalogue 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 hierarchy

NameAddressPhoneRegistration #

Library user

Register ()De-register ()

Affiliation

Reader

Items on loanMax. loans

Borrower

DepartmentDepartment phone

Staff

Major subjectHome address

Student

Multiple inheritance

Rather 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-classes.

This can lead to semantic conflicts where attributes/services with the same name in different super-classes have different semantics.

Multiple inheritance makes class hierarchy reorganisation more complex.

Multiple inheritance

# Tapes

Talking book

AuthorEditionPublication dateISBN

Book

SpeakerDurationRecording date

Voice recording

Object aggregation

An aggregation model shows how classes that are collections are composed of other classes.

Aggregation models are similar to the part-of relationship in semantic data models.

Object aggregation

Videotape

Tape ids.

Lecturenotes

Text

OHP slides

Slides

Assignment

Credits

Solutions

TextDiagrams

Exercises

#ProblemsDescription

Course titleNumberYearInstructor

Study pack

Object behaviour modelling

A behavioural model shows the interactions between objects to produce some particular system behaviour that is specified as a use-case.

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

Issue of electronic items

:Library User

Ecat:Catalog

Lookup

Issue

Display

:Library ItemLib1:NetServer

Issue licence

Accept licence

Compress

Deliver

Sequence Diagram

Objects & actors are listed along top of the diagram with a dotted line drawn vertically

The rectangle on dotted line indicated the lifeline of the object

Read the sequence of interaction from top to bottom

The annotation on arrow show the calls to the objects, their parameter & return value

Alternatives is used for conditions in square bracket

View Patient Information

Order processing

Sequence diagram describing data collection

CASE workbenches

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

Analysis and design workbenches support system modelling 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.

An analysis and design workbench

Centralinformationrepository

Codegenerator

Querylanguagefacilities

Structureddiagramming

tools

Datadictionary

Reportgenerationfacilities

Design, analysisand checking

tools

Formscreation

tools

Import/exportfacilities

Analysis workbench components Diagram editors Model analysis and checking tools Repository and associated query

language Data dictionary Report definition and generation tools Forms definition tools Import/export translators Code generation tools

Model-driven engineering

Model-driven engineering (MDE) is an approach to software development where models rather than programs are the principal outputs of the development process.

The programs that execute on a hardware/software platform are then generated automatically from the models.

Proponents of MDE argue that this raises the level of abstraction in software engineering so that engineers no longer have to be concerned with programming language details or the specifics of execution platforms.

Chapter 5 System modeling

64

Usage of model-driven engineering Model-driven engineering is still at an early stage of

development, and it is unclear whether or not it will have a significant effect on software engineering practice.

Pros Allows systems to be considered at higher levels of

abstraction Generating code automatically means that it is cheaper

to adapt systems to new platforms. Cons

Models for abstraction and not necessarily right for implementation.

Savings from generating code may be outweighed by the costs of developing translators for new platforms.

65

Model driven architecture

Model-driven architecture (MDA) was the precursor of more general model-driven engineering

MDA is a model-focused approach to software design and implementation that uses a subset of UML models to describe a system.

Models at different levels of abstraction are created. From a high-level, platform independent model, it is possible, in principle, to generate a working program without manual intervention.


66

Types of model

A computation independent model (CIM) These model the important domain abstractions used in a

system. CIMs are sometimes called domain models. A platform independent model (PIM)

These model the operation of the system without reference to its implementation. The PIM is usually described using UML models that show the static system structure and how it responds to external and internal events.

Platform specific models (PSM) These are transformations of the platform-independent

model with a separate PSM for each application platform. In principle, there may be layers of PSM, with each layer adding some platform-specific detail.


67

MDA transformations68


Multiple platform-specific models

69


Agile methods and MDA

The developers of MDA claim that it is intended to support an iterative approach to development and so can be used within agile methods.

The notion of extensive up-front modeling contradicts the fundamental ideas in the agile manifesto and I suspect that few agile developers feel comfortable with model-driven engineering.


70

Executable UML

The fundamental notion behind model-driven engineering is that completely automated transformation of models to code should be possible.

This is possible using a subset of UML 2, called Executable UML or xUML.


71

Features of executable UML To create an executable subset of UML, the

number of model types has therefore been dramatically reduced to these 3 key types: Domain models that identify the principal

concerns in a system. They are defined using UML class diagrams and include objects, attributes and associations.

Class models in which classes are defined, along with their attributes and operations.

State models in which a state diagram is associated with each class and is used to describe the life cycle of the class.

72

Key points

Behavioral models are used to describe the dynamic behavior of an executing system. This behavior can be modeled from the perspective of the data processed by the system, or by the events that stimulate responses from a system.

Activity diagrams may be used to model the processing of data, where each activity represents one process step.

State diagrams are used to model a system’s behavior in response to internal or external events.

Model-driven engineering is an approach to software development in which a system is represented as a set of models that can be automatically transformed to executable code.


73

SYSTEM MODELS MUHAMMAD RIZWAN. Objectives To explain why the context of a system should be modelled...

Documents

Transcript of SYSTEM MODELS MUHAMMAD RIZWAN. Objectives To explain why the context of a system should be modelled...