1. Software Specification Models
Software Engineering
Software Specification Models

2. The Waterfall Model Requirements Definition System and Software design
Implementation
and Unit Testing
Integration and
System Testing
Operation and
Maintenance

3. ANALYSIS PHASE
The development process starts with the analysis phase. This phase results in a specification document that shows what the software will do without specifying how it will be done.
The analysis phase can use two separate approaches, depending on whether the implementation phase is done using a procedural programming language or an object-oriented language.

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

5. Stages of Design Problem understanding Identify one or more solutions
Look at the problem from different angles to discover the design requirements.
Identify one or more solutions
Evaluate possible solutions and choose the most appropriate depending on the designer's experience and available resources.
Describe solution abstractions
Use graphical, formal or other descriptive notations to describe the components of the design.
Repeat process for each identified abstraction until the design is expressed in primitive terms.

6. Requirements Specification: Approaches
• Natural language
• Structured natural language
• Design description language
• Requirements specification language
• Graphical notation
• Formal specification

7. 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

8. Example DFD: Enrolling in a University
In Gane and Sarson notation

9. 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

10. SYMBOLS USED IN A DFD
Actions performed on data so that they are transformed, stored or distributed.
PROCESS
DATA FLOW
E.g. Result of a query to a database, contents of a printed report : data that moves together to common destinations

11. Data Flow Diagrams Process3
Cashier
Sell
Stock

12. SYMBOLS USED IN A DFD
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 referred to as external entities as they are outside the system.

13. Data Flow Diagrams Data Flows
Customer Details
Data Flow (usual)
Bi-directional Flow (rare)
Flow Between External Entities (for convenience)
Resource Flow (for convenience)
Goods
Cosmetics

14. DFD Shapes from Visio
Visio 2000
Visio 5.x

17. Data Flow Diagrams Manager Decomposing Data Flow Diagrams Stock List
Purchase Order
1 Order Stock
Produce
Stock
List
1.1
Record
Purchase
Order
1.2 * *
Stock List
Purchase Order
Stock
File M2
Purchase Order
Cabinet M1

18. Example Data Flow Diagram: Book Shipping and Receiving System
Alternate shape
Data Flow Diagrams

19. Example: University Admissions
Rejection
Application
form
Completed
application
Receive
application
Evaluate
Applicant
Offer

20. Example: University Admissions Assemble Application Stage
Acknowledgment
Acknowledgment
Application
form
Completed
application
AND
Evaluation
request
Initiate
evaluation
Receive
Applicant
AND
Supporting
information
Applicant
database
Pending
database

21. Example: University Admissions Process Completed Application Stage
Rejection
Evaluation
request
Acceptance
Offer
Financial
aid
Evaluation
Special
request
Applicant
database

22. Reading a DFD

23. DFD Example

24. 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
sides of context process box = system boundary
Example context diagram for library, inputs= book request, book return and output = book; external entity = student.
Go through the case study - context Fig 3.4 pg 32; level 1- Fig 3.5 pg 32 level 2 - Fig 3.6 pg 33 4
BCS - GP1 4

25. Relationship Among DFD levels

26. Top-Down Modeling – Process Decomposition
Draw data flow diagrams for what is happening inside each Level 0 function, etc….
Context Diagram
System
Level 0 1 2 3
Level 1
3.3
3.1
3.2
Level 2

27. Level 0 - Context Diagram
models system as one process box which represents scope of the system
identifies external entities and related inputs and outputs
Additional notation - system box

28. Context Diagram Staff Assignment Payment Campaign Manager Accountant
Client
Agate
Campaign
Management
System
Staff Grade
Staff
Contact
Advert Completion
Budget
Client Contact
Campaign Staff
Advert
Staff
Concept Note
Concept Note

29. 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

30. Top Level Diagram (Level 1)
Client 1.
Record
Clients
Clients 4.
Maintain
Staff
Campaign Manager
Staff
Accountant
Client
Staff
Staff Grade
Staff Members
Payment
Campaign
Staff
Staff
Advert Completion 2.
Plan and
Manage
Campaigns
Campaigns 5.
Manage
Adverts
Staff
Contact
Budget
Campaign
Staff Assignment
Contact
+ Completion Date
Client Contact
Cost
Adverts
Campaign Staff
Advert 3.
Prepare
Adverts
Advert 6.
Browse
Concept
Notes
Concept
Note
Staff
Concept Note
Concept Note
Concept
Note
Concept
Note
Notes

31. 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 user understand where the process fits into the overall system

32. Level 2 Diagram Staff Members Client Contact Staff 5.1 Set Client
Adverts
Advert Completion
5.2
Set Advert Completed
Completion Date

33. 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 identify process not to represent any order of processing
Data store numbers usually D1, D2, D3...

34. Labelling
Process label - short description of what the process does, e.g. Price order
Data flow label - noun representing the data flowing through it e.g. Customer payment
Data store label - describes the type of data stored
Make labels as meaningful as possible

35. Level 0 Context diagram CUSTOMER KITCHEN Food ordering system
RESTAURANT MANAGER

36. Level 0 Context diagram CUSTOMER KITCHEN Customer Order
Customer Order
Food ordering system
Food Order
Receipt
Management Reports
RESTAURANT MANAGER

37. 1.0 3.0 2.0 4.0 Receive and transform Customer Food Order
Update Goods Sold file
2.0
Update Inventory file
4.0
Produce Management Reports

38. CUSTOMER
KITCHEN
1.0
Receive and transform Customer Food Order
Customer Order
Food Order
Receipt
3.0
Update Goods Sold file
2.0
Update Inventory file D2
Inventory File
Goods Sold File D1
4.0
Produce Management Reports
RESTAURANT MANAGER
Management Reports

39. CUSTOMER
KITCHEN
1.0
Receive and transform Customer Food Order
Customer Order
Food Order
Receipt
Goods
Sold
Inventory
Data
3.0
Update Goods Sold file
2.0
Update Inventory file
Inventory Data
Goods Sold Data D2
Inventory File
Goods Sold File D1
4.0
Produce Management Reports
Daily Inventory Depletion Amounts
Daily Goods Sold Amount
RESTAURANT MANAGER
Management Reports

40. DFD Example : Payroll

41. 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

42. DFD Package data order Customer Process order invoice Customer data
Package details
Customer
order
Process order
invoice
Credit status
Customer data

43. DFD (2) Package data order Customer Customer data
Package details
Customer
order
Verify order is valid
Assemble order
invoice
details
Credit status
Customer data

44. Place order at supplier
DFD (3)
Details of package to be ordered
Batched order
Verify order is valid
Place order at supplier
Pending orders
Address or telephone
Software Supplier

45. DFD (4) Package data order Customer Customer data Account receivable
Package details
Customer
order
Verify order is valid
Assemble order
invoice
details
payment
Credit status
Customer data
Payment to invoice
Account receivable

46. Creating Data Flow Diagrams Lemonade Stand Example

47. Creating Data Flow Diagrams
Example
Steps:
The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams.
Construct Context Level DFD (identifies sources and sink)
Construct Level 0 DFD (identifies manageable sub processes )
Construct Level 1- n DFD (identifies actual data flows and data stores )

48. Creating Data Flow Diagrams
Example
Create a list of activities
Think through the activities that take place at a lemonade stand.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product

49. Creating Data Flow Diagrams
Example
Create a list of activities
Also think of the additional activities needed to support the basic activities.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor

50. Creating Data Flow Diagrams
Example
Construct Context Level DFD (identifies sources and sink)
Create a context level diagram identifying the sources and sinks (users).
Context Level DFD
Sales Forecast
CUSTOMER
0.0
Lemonade System
EMPLOYEE
Order
Production Schedule
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Product Served
Pay
Payment
Time Worked
Received Goods
Payment
Purchase Order
VENDOR

51. Creating Data Flow Diagrams
Example
Construct Level 0 DFD (identifies manageable sub processes )
Create a level 0 diagram identifying the logical subsystems that may exist.
Level 0 DFD
1.0
Sale
Sales Forecast
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Customer Order
Product Ordered
CUSTOMER
Payment
2.0
Production
EMPLOYEE
Production Schedule
Product Served
Inventory
Received Goods
VENDOR
3.0
Procure-ment
Purchase Order
Order Decisions
Payment
Pay
Time Worked
4.0
Payroll

52. Creating Data Flow Diagrams
Example
Construct Level 1- n DFD (identifies actual data flows and data stores )
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
CUSTOMER
Customer Order
Request for Forecast
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
ORDER
1.1
Record Order
1.3
Produce Sales Forecast
Severed Order
Payment
Sales Forecast
1.2
Receive Payment
PAYMENT

53. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Product Order
ORDER
2.1
Serve Product
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Quantity Severed
RAW MATERIALS
Production Schedule
2.2
Produce Product
Quantity Used
INVENTORTY
Production Data
2.3
Store
Product
Quantity Produced & Location Stored

54. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Order Decision
PURCHASE ORDER
3.1
Produce Purchase Order
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Quantity On-Hand
RAW MATERIALS
Quantity Received
Received Goods
3.2
Receive Items
RECEIVED ITEMS
Payment Approval
3.3
Pay Vendor
VENDOR
Payment

55. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Time Worked
TIME CARDS
4.1
Record Time Worked
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Employee ID
EMPLOYEE
Payroll Request
4.2
Calculate Payroll
Unpaid time cards
PAYROLL
Payment Approval
4.3
Pay Employee
PAYMENTS
Payment

56. Process Decomposition
1.0
Sale
1.1
Record Order
1.2
Receive Payment
2.0
Production
2.1
Serve Product
2.2
Produce Product
2.3
Store
Product
0.0
Lemonade System
3.0
Procure-ment
3.1
Produce Purchase Order
3.2
Receive Items
3.3
Pay Vendor
4.0
Payroll
4.1
Record Time Worked
4.2
Calculate Payroll
4.3
Pay Employee
Context Level
Level 0
Level 1

57. 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.

58. 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

59. 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

60. Bus Garage Context Diagram
Mechanical problem
to be repaired
Fixed mechanical
problems
Supervisor
Helper
Bus Repair Process
System
Repair summary
Labor
List of parts used
Inventory Management System
Labor
Labor, parts cost details
Mechanic
Accounting

61. Burger’s Order Processing System
Draw the Burger’s context diagram
System
Order processing system
External entities
Kitchen
Restaurant
Customer
Processes
Customer order
Receipt
Food order
Management report

62. Joe’s builders’ suppliers has a shop and a yard
Joe’s builders’ suppliers has a shop and a yard. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the 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 new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.

63. Context diagram

64. Level-1 DFD processes
Joe’s builders’ suppliers has a shop and a yard. His system is entirely manual. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the 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 new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.
Verbs:
Passive: has
Buy supplies
Picks stock items
Writes orders
Pays joe
Stamps docket
Takes docket to yard
Hands it to foreman
Gets items
Gives them to builder
Builder signs docket
Takes copy as receipt
Looks around yard and reorders
Records order in order book
Foreman takes delivery – checks
Foreman pays supplier
Staples receipt to order book
Produces financial report

65. Level 1 current physical

66. Buy Supplies

67. Get Items

68. Reorder supplies

69. Restock

70. Evolutionary software process models
The waterfall model is appropriate when requirement changes are limited.
True b. False
Evolutionary software process models
Are iterative in nature
Can easily accommodate product requirements changes
Do not generally produce throwaway systems
All of the above
The first step in project planning is to
determine the budget.
select a team organizational model.
determine the project constraints.
establish the objectives and scope.

71. Give the time network chart for a giving example based on the following project data:
i) The project involved 7 tasks:T1, T2, T3, T4, T5, T6, T7;
ii) The tasks have the following durations: T1 (3 weeks), T2 (2 weeks), T3 (4 weeks), T4 (1 week), T5 (3 weeks), T6 (2 weeks), T7 (4 weeks);
iii) Tasks T4 and T5 are dependent on Milestone M1 produced by Task T1;
iv) Task T5 is also dependent on Milestone M2 produced by Task T2;
v) Task T6 is dependent on Milestones M3 and M5 produced Task T3 and Task T5 respectively

72. Suggest an appropriate software process model that might be used as a basis for managing the development of the following systems:
a) an e-auction system which will run over the web,
b) a modification to a computer game,
c) a system to control radiation therapy administered to patients in a hospital,
d) a new virtual learning environment for a college or school, and
e) an interactive web-based system that allows customers to review films available and book tickets for a cinema.
In each case, justify your choice by giving reasons that take into account the type of system that is to be developed.

73. Case Study: Train Routing
Consider a system designed to route trains automatically
Upon arrival at some light
train is assigned a new route
which takes it to the next light
The system selects proper position for each switch along the route.

74. Case Study: Train Routing
Data stores
network layout
traffic
Stimuli
arrival at a light
unlock side protection lights
identify blocked trains
reprocess their routes
get new route
lock side protection lights on red
turn light green (if successful)

75. Running Case Study: Elevator
Consider the development of an elevator control system for a 10-story residential building.
Discuss possible objectives and assign priorities
fire evacuation
safe operation: fire, door, alignment, accelartion, stopping at extremes
rush hour effectiveness
reliability and dependability
timely delivery of single requests
energy conservation
Identify visible interfaces
button, lights, sensors, alarm, climate controls, etc.
Outline general capabilities
accept valid calls and light the button
announce arrival and reset call lights
respond to fire alarm
support environmental controls
provide for continuous alignment
activate buzzer for open door
...
Identify and separate constraints
single processor
all sensors are memory mapped
automatic restart capability

76. Centralized Controller
All external interfaces have been identified
The specification does not rule out a distributed implementation …
… but provides a concrete high-level architecture to allow further specification and refinement