lect5 se_specification.ppt

8/10/2019 Lect5 SE_Specification.ppt

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Software Specification Models

Software Engineering


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The Waterfall Model

Requirements

Definition

Implementation

and Unit Testing

Integration and

System Testing

Operation and

Maintenance

System andSoftware design


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Focus on models

Operational processInformation

System

Model


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ANALYSIS PHASE

The development process starts with the analysis

phase. This phase results in a specification

document that shows what the software will dowithout specifying how it will be done. The analysis

phase can use two separate approaches, depending

on whether the implementation phase is done usinga procedural programming language or an object-

oriented language.


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System modelling

System modelling helps the analyst

to understand the functionality of

the system and models are used to

communicate with customers


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Stages of Design

Problem understanding

Look at the problem from different angles to discover the

design requirements.

Identify one or more solutions

Evaluate possible solutions and choose the mostappropriate depending on the designer's experience and

available resources.

Describe solution abstractions

Use graphical, formal or other descriptive notations todescribe the components of the design.

Repeat process for each identified abstraction

until the design is expressed in primitive terms.


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Requirements Specification: Approaches

Natural language

Structured natural language

Design description language

Requirements specification language

Graphical notation Formal specification


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Procedure-oriented analysis

Procedure-oriented analysisalso called

structured analysis or classical

analysis

is the analysis process used ifthe system implementation phase will

use a procedural language. The

specification in this case may use severalmodeling tools, but we discuss only a

few of them here.


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Data flow diagrams

Data flow diagrams show the movement of data in the

system.


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Entity-relationship diagrams

Another modeling tool used during the analysis

phase is the entity-relationship diagram. Thisdiagram is also used in database design.


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Entity-Relation Diagram

An entity

A relation between

entities

An entity or relation

attribute

An inheritance

relation


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Example: CS 311 Project

Student

CS311

Student

Major

Project

5 to 7

1

Member of

Person

Client

1

Tech contact

0:n0:n

0:n


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Example: CS 305Project

Student

CS305

Student

Major

Project

5 to 7

1

Member of

Person

Client

1

Tech contact

0:n0:n

0:n


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State diagrams

State diagrams provide another useful tool that

is normally used when the state of the entities

in the system will change in response to events.

As an example of a state diagram, we show the

operation of a one-passenger elevator. When a

floor button is pushed, the elevator moves in

the requested direction. It does not respond toany other request until it reaches its

destination.


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An example of a state diagram


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Object-oriented analysis

Object-oriented analysis is theanalysis process used if the

implementation uses an object-oriented language. The

specification document in this casemay use several tools.


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Use case diagrams

A use-case diagram gives the users view of a system: it

shows how users communicate with the system. A use-casediagram uses four components: system, use cases, actors and

relationships. A system, shown by a rectangle, performs a

function.


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Class diagrams

The next step in analysis is to create a class

diagram for the system. For example, we cancreate a class diagram for our old-style

elevator. To do so, we need to think about the

entities involved in the system.


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State chart

After the class diagram is finalized, a statechart can be prepared for each class in the

class diagram. A state chart in object-

oriented analysis plays the same role as

the state diagram in procedure-oriented

analysis.


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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 t ime 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

showsReady to cook

.Operation Oven in operation. Interior oven light is on. Display shows the

timer countdown. On complet ion of cooking, the buzzer is

sounded for 5 seconds. Oven light is on. Display shows Cooking

complete while buzzer is sounding.


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Microwave oven modelFull power

Enabled

do: operateoven

Fullpower

Halfpower

Halfpower

Fullpower

Number

TimerDooropen

Doorclosed

Doorclosed

Dooropen

Start

do: set power = 600

Half power

do: set power = 300

Set timedo: get numberexit: set time

Disabled

Operation

Timer

Cancel

Waiting

do: display time

Waiting

do: display time

do: display 'Ready'

do: display

'Waiting'


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Microwave oven operation

Cook

do: 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


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Data Flow Diagrams

DFDs model the system from a functionalperspective

Tracking and documenting how the data

associated with a process is helpful todevelop 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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4 Main Elements

external entity - people or organisations that

send data into the system or receive data from

the system

process- models what happens to the data i.e.transforms incoming data into outgoing data

data store- represents permanent data that is

used by the system data flow- models the actual flow of the data

between the other elements


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PROCESS

DATA FLOW

E.g. Result of a query to adatabase, contents of a printed

report : data that moves

together to common

destinations

Actions performed on data

so that they are

transformed, stored or

distributed.

SYMBOLS USED IN A DFD


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DATA STORE

A physical location to hold

data e.g. a file folder or

notebook etc.

SOURCE/SINK Origin and/or destination

of the data. Often referredto as external entities as

they are outside the

system.

SYMBOLS USED IN A DFD


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Example: University Admissions

Applicant

Applicationform Receive

application

Completedapplication

Evaluate

Rejection

Offer


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Assemble Application Stage

Applicant

Applicationform

Receive

Completedapplication

Supporting

information

Pending

database

Acknowledgment

Initiate

evaluation

Applicant

database

Evaluation

request

AND

AND

Acknowledgment


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Process Completed Application Stage

Rejection

Evaluation

Applicant

database

Evaluationrequest Acceptance

Financial

aid

Offer

Specialrequest


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DFD Shapes from Visio

From Flow Chart /

Data Flow Diagram

Process

Data Store

External Entity

From Software Diagram /

Gane-Sarson DFD

Process

ID #

ID

#

External

Entity

Data Store1

External

Entity

Data Store

Process

From Flow Chart /

Data Flow Diagram

Visio 5.x Visio 2000


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Reading a DFD


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4

Levelled DFDs

Even a small system could have many

processes and data flows and DFD could

be large and messy use levelled DFDs - view system at different

levels of detail

one overview and many progressively greater

detailed views


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Relationship Among DFD levels


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Level 0 - Context Diagram

models system as one process box whichrepresents scope of the system

identifies external entities and related inputs

and outputs Additional notation - system box

System boxExternal

entity

Data flow out

Data flow in


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Level 1 - overview diagram

gives overview of full system

identifies major processes and data flows between

them

identifies data stores that are used by the major

processes

boundary of level 1 is the context diagram


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Level 2 Diagrams

level 1 process is expanded into more detail

each process in level 1 is decomposed to show its

constituent processes

Level 2 diagrams may not be needed for all level

1 processes

Correctly numbering each process helps the userunderstand where the process fits into the overall

system


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Numbering

On level 1 processes are numbered

1,2,3

On level 2 processes are numbered x.1,

x.2, x.3 where x is the number of the

parent level 1 process

Number is used to uniquely identifyprocess notto represent any order of

processing

Data store numbers usually D1, D2, D3...


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Labelling

Process label - short description of what

the process does, e.G. Price order

Data flow label - noun representing thedata flowing through it e.G. Customer

payment

Data store label - describes the type ofdata stored

Make labels as meaningful as possible


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Context Diagram

Agate

Campaign

Management

System

Campaign

Manager

Client

Budget

CampaignStaff

Campaign

Advert

Staff Assignment

Accountant

Concept Note

StaffConcept Note

Staff

Staff Grade

Staff

Contact

Payment

Advert Completion

Client Contact


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Top Level Diagram (Level 0)

1.

Record

Clients

Campaign

Manager

Client

Staff Assignment

CampaignStaff

Campaign

Advert

Accountant

Concept Note

Staff

Concept

Note

Staff

Staff Grade

Staff

Contact

Payment

Advert Completion

Client Contact

3.Prepare

Adverts

Notes

6.

Browse

Concept

Notes

Concept

Note

Concept Note

4.

Maintain

Staff

5.

Manage

Adverts

Adverts

Advert

Contact

+ Completion Date

Clients

Client

2.

Plan and

Manage

Campaigns

Staff Members

Staff

Budget

Cost

Concept

Note

Campaigns

Campaign

Staff

Staff


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Level 1 Diagram

Advert Completion

Client Contact

5.1

Set ClientContact

Adverts

Contact

Staff Members

Staff

Completion Date5.2

Set AdvertCompleted


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Example

Alexsoft shop buys software from various suppliers

and sells it to the public

The shop stocks popular software packages and

orders as required The shop sells monthly about 300 packages

The shop need to be computerized


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System requirements

Business functions, account payable, accounts

receivable and inventory

The system is batch or online

One computer with appropriate configuration


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DFD

Customerorder

invoice

Processorder

Package data

Customer data

Package details

Credit status


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DFD (2)

Customerorder

invoice

Assemble

order

Package data

Customer data

Package details

Credit status

Verify order

is valid

details


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DFD (3)

Pending orders

Details of package to

be ordered

Software

Supplier

Place order at

supplier

Batched order

Address or telephone

Verify order

is valid


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DFD (4)

Customerorder

invoice

Assemble

order

Package data

Customer data

Package details

Credit status

Verify order

is valid

details

Payment to

invoice

payment

Account

receivable


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Food

orderingsystem

0

CUSTOMER KITCHEN

RESTAURANT

MANAGER

Food Order

Management

Reports

Customer Order

Receipt

Level 0 Context diagram


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1.0

Receive and

transform

Customer FoodOrder

2.0

Update

Inventoryfile

3.0

Update

Goods

Sold file

4.0

Produce

Management

Reports

CUSTOMER KITCHEN


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1.0

Receive and

transform

Customer FoodOrder

2.0

Update

Inventoryfile

3.0

Update

Goods

Sold file

4.0

Produce

Management

Reports

CUSTOMER KITCHEN

RESTAURANT

MANAGER

Food Order

Customer Order

Receipt

ManagementReports

Goods Sold

FileD1

D2 Inventory File

CUSTOMER KITCHEN


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1.0

Receive and

transform

Customer FoodOrder

2.0

Update

Inventoryfile

3.0

Update

Goods

Sold file

4.0

Produce

Management

Reports

CUSTOMER KITCHEN

RESTAURANT

MANAGER

Food Order

Customer Order

Receipt

Management

Reports

Goods Sold

FileD1

D2 Inventory File

Goods

Sold

Inventory

Data

Goods

Sold Data

Inventory Data

Daily Goods Sold

Amount

Daily Inventory Depletion Amounts


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DFD Example : Payroll


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Creating Data Flow Diagrams

Lemonade Stand Example



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Steps:

1. Create a list of activities

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 )

4. Construct Level 1- n DFD

(identifies actual data flows and data stores )

Example

The operations of a simplelemonade stand will be used

to demonstrate the creation

of dataflow diagrams.



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1. Create a list of activitiesExample

Think through the activitiesthat take place at a lemonade

stand.

Customer Order

Serve Product

Collect PaymentProduce Product

Store Product


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Example

Group these activities insome logical fashion,

possibly functional areas.

Customer Order

Serve Product

Collect Payment

Produce Product

Store Product

Order Raw MaterialsPay for Raw Materials

Pay for Labor

1. Create a list of activities



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0.0

Lemonade

System

EMPLOYEECUSTOMER

Pay

Payment

Order

Context Level DFD

Example

Create a context leveldiagram identifying the

sources and sinks (users).

Customer Order

Serve ProductCollect Payment

Produce Product

Store Product

Order Raw Materials

Pay for Raw Materials

Pay for Labor

VENDOR

PaymentPurchase Order

Production Schedule

Received GoodsTime Worked

Sales Forecast

2. Construct Context Level DFD

(identifies sources and sink)

Product Served



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g g

Level 0 DFD

Example

Create a level 0 diagramidentifying the logical

subsystems that may exist.

Customer Order


Produce Product

Store Product

Order Raw Materials


Pay for Labor

3. Construct Level 0 DFD

(identifies manageable sub processes )

2.0

ProductionEMPLOYEE

Production

Schedule

1.0

Sale

3.0Procure-

ment

Sales Forecast

Product Ordered

CUSTOMER

Pay

Payment

Customer Order

VENDOR

Payment

Purchase OrderOrder

Decisions

Received Goods

Time Worked

Inventory

Product Served

4.0

Payroll



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g g

Level 1 DFD

Example

Create a level 1decomposing the processes

in level 0 and identifying

data stores.

4. Construct Level 1- n DFD

(identifies actual data flows and data stores )

1.3

Produce

Sales

ForecastSales ForecastPayment

Customer Order


Produce Product

Store Product

Order Raw Materials


Pay for Labor

1.1Record

Order

Customer Order

ORDER

1.2

ReceivePayment

PAYMENT

Severed Order

Request for Forecast

CUSTOMER



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g g

Level 1 DFD

Example



data stores.

4. Construct Level 1 (continued)

Customer Order


Produce Product

Store Product

Order Raw Materials


Pay for Labor

2.1

ServeProduct

Product Order

ORDER

2.2

Produce

Product

INVENTORTY

Quantity Severed

Production

Schedule

RAW

MATERIALS

2.3

Store

Product

Quantity Produced &

Location Stored

Quantity Used

Production Data



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g g

Level 1 DFD

Example



data stores.


Customer Order


Produce Product

Store Product

Order Raw Materials


Pay for Labor

3.1

Produce

Purchase

Order

Order DecisionPURCHASE

ORDER

3.2

Receive

Items

Received

Goods

RAWMATERIALS

3.3

Pay

Vendor

Quantity

Received

Quantity On-Hand

RECEIVED

ITEMS

VENDOR

Payment Approval

Payment



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g g

Level 1 DFD

Example



data stores.


Time Worked

Customer Order


Produce Product

Store Product

Order Raw Materials


Pay for Labor

4.1

Record

Time

Worked

TIME CARDS

4.2

Calculate

Payroll

Payroll Request

EMPLOYEE

4.3

Pay

Employe

e

Employee ID

PAYROLL

PAYMENTS

Payment Approval

Payment

Unpaid time cards

Process Decomposition


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p

4.1

Record

Time

Worked

4.2

Calculate

Payroll

4.3

Pay

Employe

e

3.1

Produce

Purchase

Order

3.2

Receive

Items

3.3

Pay

Vendor

2.1

Serve

Product

2.2

Produce

Product

2.3

Store

Product

1.1

Record

Order

1.2

Receive

Payment

2.0

Production

1.0

Sale

3.0

Procure-

ment

4.0

Payroll

0.0

Lemonade

System

Level 0 Level 1Context Level

DFD Example: Bus Garage Repairs


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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 isused for billing by the Accounting Department,

parts monitoring by the inventory management

computer system and a performance review by the

supervisor.



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(contd)

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



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(contd)

Data stores: Personnel file

Repairs file

Bus master list

Parts list

Data flows:

Repair order

Bus record

Parts record

Employee timecard

Invoices

Bus Garage Context Diagram


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Bus

Mechanic

Helper Bus

RepairProcess

System

Supervisor

Accountin

g

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


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CSUB Burgers Order Processing System

Draw the CSUB Burgers context diagram

System

Order processing system

External entities

Kitchen

Restaurant

Customer

Processes

Customer order

Receipt

Food order

Management report

Joesbuilders suppliers has a shop and a yard. He has astock list on the wall of his shop complete with prices


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stock list on the wall of his shop, complete with prices.When a builderwants to buy supplies, he goes into theshop and picks the stock items from the list. He writeshis order on a duplicate docket and pays

Joe, who stamps

the docket as paid. The builder takes the duplicate docketand he goes to the yard and hands it to the yard foreman.The yard foreman gets the ordered items from the yardand gives them to the builder. The builder signs the

duplicate docket and leaves one copy with the foremanand takes one copy as a receipt. Every week, Joe looksaroundthe yard to see if any of his stock is running low.He rings up the relevant suppliers and reorders stock.He records the order in his order book, which is kept in

the yard. The yard foreman takes delivery of the newstock and checks it against what has been ordered. He

pays for it on delivery and staples the receipt into theorder book. At the end of every month, Joe goes throughall the dockets and the order book and produces afinancial report for the shareholders.


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Context diagram

Joe'sYard

Joe Customer

Supplier

Shareholders

Docket &

Payment

Signed docket

Supply needs

Supply invoiceSupply order& payment

financialreport

Level-1 DFD processesJoes builders suppliers has a shop and a yard His system is


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Joe sbuilders suppliers has a shop and a yard. His system isentirely manual. He has a stock list on the wall of hisshop, complete with prices. When a builder wants tobuy

supplies, he goes into the shop andpicks the stock itemsfrom the list. He writeshis order on a duplicate docketandpaysJoe, who stampsthe docket as paid. The buildertakes the duplicate docket and he goes to the yard andhandsit to the yard foreman. The yard foreman getsthe

ordered items from the yard and gives them to thebuilder. The builder signs the duplicate docket andleavesone copy with the foreman and takesone copy as areceipt. Every week, Joe looks aroundthe yard to see ifany of his stock is running low. He rings upthe relevantsuppliers and reordersstock. He recordsthe order in hisorder book, which is keptin the yard. The yard foremantakes deliveryof the new stock and checksit against whathas been ordered. Hepaysfor it on delivery and staples

the receipt into the order book. At the end of everymonth Joe oes throu h all the dockets and the order


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Level 1 current physical

Customer

Buysupplies

20

getitems

12

Reorder

supplies

21

Restock

22

*

Producefinancialreport

Joe's Office5

Joe

Orderbook

M3

DocketM1

Money

stock

Shareholders

Supplier

Foreman

*

Taketo

yard

11Supply needs

financialreport

Docket &Payment

Supply order

Docket

Signed docket

Signed docket

Signed docket

Payment

required stock

required stock

completed

docket copycompleted

docket copy

Supply order

supplies

supplies

Payment Payment

Supplierreceipt

Supplierreceipt

completeddocket copy

buildersignature


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Buy Supplies

Buy supplies20 DocketM1

Money

Customer

*

WritesOrder

20.1

*

PaysJoe

20.2*

StampDocket(signatu-

re)

20.3

Docket

Payment

Docket

Payment

Docket


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Get Items

get items12

Foreman

stock

*

Give itemsto customer

12.1

*

Get buildersignature

12.2

*

Give

copyas receipt

12.3

Customer

Signed docket

required stock

buildersignature

Signed docket

completeddocket copy completed

docket copy


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Reorder supplies

Reorder supplies21

Orderbook

M3

Joe

*

Reorderfromyard

21.1

*

Recordorder

21.2

Supply order

Supply needs

Supply needs


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Restock

Restock22

stock

Orderbook

M3

Supplier

Money

*

Takedelivery

22.1

*

Paysupplier

22.2

supplies

Payment

Supplierreceipt

Supply order

supplies

Payment

Supply order

lect5 se_specification.ppt

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