1. System Analysis (Analysing Requirements)
CSC Systems Analysis and Design

2. CSC 2202 Systems Analysis and Design
Outline
Objectives
Types of Requirements
Functional requirements
Non-Functional requirements
Structured Analysis techniques
Data flow diagrams
Data dictionary
Process descriptions
Entity Relationship Diagrams
Review questions
CSC Systems Analysis and Design

3. CSC 2202 Systems Analysis and Design
Objectives
Explain the structured analysis process and identify its elements
Explain data flow diagrams their use in documenting requirements
Describe the data dictionary and its use in documentation.
CSC Systems Analysis and Design

4. Requirements Analysis
Requirements analysis describes all the tasks of instigation, scoping and definition of a new or altered computer system.
It enables business analysts or software developers identify the needs or requirements of a client in order to design a solution
CSC Systems Analysis and Design

5. CSC 2202 Systems Analysis and Design
Types of Requirements
Functional requirements
Describe what the system should do
Non-functional requirements
Consists of Constraints that must be adhered to during development (design and implementation)
Operative word: ‘Constraints.’
CSC Systems Analysis and Design

6. Functional requirements
What inputs the system should accept
What outputs the system should produce
What data the system should store that other systems might use
What computations the system should perform
The timing and synchronization of the above
CSC Systems Analysis and Design

7. Non-functional requirements
Non-functional requirements are global constraints on a computer system
e.g. development costs, operational costs, performance, reliability,
The challenge of Non-functional requirements:
Hard to model
Usually stated informally, and so are:
often contradictory,
difficult to enforce during development
difficult to evaluate for the customer prior to delivery
CSC Systems Analysis and Design

8. Non-functional requirements
Define system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations.
Process requirements may also be specified mandating a particular programming language or development method
Non-functional requirements may be more critical than functional requirements. If these are not met, the system is useless
CSC Systems Analysis and Design

9. CSC 2202 Systems Analysis and Design
Examples of NFR
Interface requirements
how will the new system interface with its environment?
User interfaces and “user-friendliness”
Interfaces with other systems
Performance requirements
Time - response time
Throughput - transactions per second
CSC Systems Analysis and Design

10. CSC 2202 Systems Analysis and Design
Examples of NFR
Security
permissible information flows
Or who can do what
Survivability – e.g. system will need to survive fire natural catastrophes, etc
Operating requirements
physical constraints (size, weight),
personnel availability & skill level
accessibility for maintenance
environmental conditions
CSC Systems Analysis and Design

11. CSC 2202 Systems Analysis and Design
Examples of NFR
Lifecycle requirements
Maintainability, Enhanceability, Portability, expected market or product lifespan
limits on development
E.g development time limitations, resource availability and methodological standards.
Economic requirements
e.g. restrictions on immediate and/orlong-term costs.
CSC Systems Analysis and Design

12. User Requirements Specification -URS
It is a document produced by, or on behalf of an organisation, which documents the purposes for which a system is required
Its functional requirements - usually in order of priority / gradation.
CSC Systems Analysis and Design

13. User Requirements Specification -URS
The URS document outlines precisely what the User (or customer) is expecting from this system.
The term User Requirement Specification can also incorporate the functional requirements of the system or may be in a separate document labelled the Functional Requirements Specification - the FRS.
CSC Systems Analysis and Design

14. System requirements specification
What do we agree to provide?
A structured document setting out detailed descriptions of the system services.
Written as a contract between client and contractor.
CSC Systems Analysis and Design

15. CSC 2202 Systems Analysis and Design

16. User Requirement Document
The URD has has the following
information:
Functional Requirements
Non-Functional Requirements
CSC Systems Analysis and Design

17. CSC 2202 Systems Analysis and Design
Structured Analysis
CSC Systems Analysis and Design

18. CSC 2202 Systems Analysis and Design
Structured Analysis
Examines inputs, outputs, and processes
Process-centered technique
Uses three main tools
Data flow diagrams (DFDs)
Data dictionary
Process descriptions(modeling)
Tools can be applied using computer-aided software engineering (CASE) tools
CSC Systems Analysis and Design

19. CSC 2202 Systems Analysis and Design
Analysis Models
Each modeling tool provides a different perspective on the system under investigation
Data Flow Diagrams
Data Dictionary
Process (Transform) Descriptions using:
Structured English, Action Diagrams, Decision Tables, Decision Trees, Narratives
Entity Relationship diagrams
CSC Systems Analysis and Design

20. CSC 2202 Systems Analysis and Design
Structured Analysis
It deals more with the logic of the system.
The analyst defines what the system should do.
Breaks down the system into manageable subsystems
Method defines systems inputs, processes, and outputs
Partitions systems into subsystems or modules that show a logical graphic model of information flow.
CSC Systems Analysis and Design

21. CSC 2202 Systems Analysis and Design
Structured Analysis
Objective of Structured Analysis
Is to document all the end user requirements for the proposed Information System and present these requirements in the systems requirement document.
CSC Systems Analysis and Design

22. CSC 2202 Systems Analysis and Design
Structured Analysis
Structured Analysis accomplishes the following:-
Views the system from the top to down.
Specifies the interfaces that exist between modules.
Rigorously specifies the processes or transformations that occur within each module.
CSC Systems Analysis and Design

23. Components of Structured Analysis
Data Dictionary – description of all the data used in the system.
2. Graphic Symbols – icons and conventions for identifying and describing the components of a system and relationship among these components.
3. Procedure and Process description – Formal statements using techniques and languages that enable systems analysts to describe important activities that make up a system.
4. Rules standards for describing and documenting the system correctly and completely
CSC Systems Analysis and Design

24. CSC 2202 Systems Analysis and Design
Document Flow Diagram
A diagramming technique which is used to identify physical movement of documents.
It shows where the document comes from, where it goes to, and what it is called.
The source and destination of the document are usually shown using an elliptical shape.
CSC Systems Analysis and Design

25. Document Flow Diagram for a Purchasing System1
Order
Supplier
Purchasing
Dept
Invoice
Delivery notes
Stores
CSC Systems Analysis and Design

26. CSC 2202 Systems Analysis and Design
Document Flow Diagram
For each document or communication that occurs in the system, identify the source and the target. This will help in developing a context diagram during analysis.
It is a physical data flow diagram.
CSC Systems Analysis and Design

27. Process modeling with data flow diagrams
Data Flow Diagrams – show how data moves and changes through an IS in a graphical top-down fashion. i.e. a graphic representation of a system’s components, processes and the interfaces between them.
CSC Systems Analysis and Design

28. CSC 2202 Systems Analysis and Design
Data Flow Diagrams
Data flow diagrams (DFDs) are graphical aids that describe an information system .
They represent a logical model that shows what a system does, not how it does it.
It is a network representation of a system.
Stresses flow of data within a system.
CSC Systems Analysis and Design

29. CSC 2202 Systems Analysis and Design
Data Flow Diagrams
Simplicity (only 4 symbols used) enhances communication between users and system designers
Stress processes and transformation of data within a system
“Drives” the process of system description
An iterative process
CSC Systems Analysis and Design

30. Data Flow Diagram - 4 components
A DFD comprises combinations
of 4 symbols:
External entity – rectangle
Data flow – arrow
Process - circle (Yourdon).
Data store - 2 parallel lines (Yourdon)
CSC Systems Analysis and Design

31. Data Flow Diagram - 4 symbols (Yourdon)
Customer
External Entity
Data Flow
Invoice
Process
Compute
Discount
Data Store
Customer Accounts
CSC Systems Analysis and Design

32. Data Flow Diagram - 4 symbols (Gane and Sarson convention)
CSC Systems Analysis and Design

33. CSC 2202 Systems Analysis and Design
DFD components
External Entities
Sources/destinations for data
Outside the system
Name is Noun Phrase
Conventions vary
CSC Systems Analysis and Design

34. CSC 2202 Systems Analysis and Design
DFD components
External entity :
outside the context of the system any class of people, organisation or another system
function is to supply or receive data
also called Source and Sink also called Origin and Destination
are originators or receivers of information outside the scope of the IS portrayed in the data flowing.
CSC Systems Analysis and Design

35. CSC 2202 Systems Analysis and Design
DFD components
Data flow
Show movement of data
Is a pipeline carrying data through the system
These show the movement of data between processes, external entities, and data stores in a DFD.
CSC Systems Analysis and Design

36. CSC 2202 Systems Analysis and Design
DFD components
Process
incoming data flows are processed or transformed into outgoing data flows
they portray the transformation of input data flows to output data flows in DFDs.
CSC Systems Analysis and Design

37. CSC 2202 Systems Analysis and Design
DFD components
Process/System
Numbered
Name is verb/object phrase;
Noun for high-level systems
CSC Systems Analysis and Design

38. CSC 2202 Systems Analysis and Design
DFD components
Data flows
Directed arrow
Shows data in motion
Name uniquely identifies data
Name is a noun phrase
CSC Systems Analysis and Design

39. CSC 2202 Systems Analysis and Design
DFD components
Data flow symbol
Symbol is a line with an arrowhead showing direction
A path for data to move from one part of the system to another
Might represent one or many pieces of data
At least one data flow must enter and exit each process
CSC Systems Analysis and Design

40. CSC 2202 Systems Analysis and Design
DFD components
A resource flow/physical flow
shows the flow of any physical material from its source to its destination.
They are usually restricted to early, high-level diagrams.
Used to describe the physical flow of materials considered important in the analysis.
CSC Systems Analysis and Design

41. CSC 2202 Systems Analysis and Design
DFD components
Data store
a temporary or time delayed repository or collection of data
processes can add data to, or retrieve data from, these stores
are either manual or automated inventories of data. e.g. computer files or databases, file cabinets& card files.
CSC Systems Analysis and Design

42. CSC 2202 Systems Analysis and Design
DFD components
Data Store
Static data
data held for archive or subsequent processing
Name is a noun phrase
CSC Systems Analysis and Design

43. CSC 2202 Systems Analysis and Design
DFD components
Data Stores Each store is given a reference letter 'D' - indicates a permanent computer file 'M' - indicates a manual file 'T' - indicates a transient store, one that is deleted after processing. To avoid complex flows, the same data store may be drawn several times on a diagram. Multiple instances of the same data store are indicated by a double vertical bar on their left hand edge.
CSC Systems Analysis and Design

44. CSC 2202 Systems Analysis and Design
DFD - Context Diagram
Defines the scope of the system
Provides on “outward” looking view from the system
Shows the other systems and/or groups of people that interact with the system
Shows the main flows of data
CSC Systems Analysis and Design

45. DFD - Context Diagram (cont)
Context diagram - It is a simple DFD that depicts the system being studied as it relates to other systems, the business, and the outside world – the interfaces flowing to or from external entities.
CSC Systems Analysis and Design

46. CSC 2202 Systems Analysis and Design.
Order
DFD - Context Diagram
Invoice
Order processing system
Warehouse
Customer
Picking-labels
Order-rejection-notice
Out-of-stock-notice
Context diagram of an order processing system
CSC Systems Analysis and Design

47. DFD - Context Diagram Notation.
DFD - Context Diagram Notation
CSC Systems Analysis and Design

48. Data Flow Diagram- Context Diagram
Register-Request
Student
Course-
Enrolment
Faculty
Schedule
Tuition-Bill
Student
Registration
System
Student-Bal-Due
Accounts-Receivables-Stmt
Accounts
Receivable
System
New-Bal-Due
CSC Systems Analysis and Design

49. Data Flow Diagram- Context Diagram
Airline reservation system
CSC Systems Analysis and Design

50. CSC 2202 Systems Analysis and Design
Context Diagram
One Process/System
The system/process being analyzed
Name: Usually a Noun phrase
Show Context Only
Inputs/outputs
External Entities
No Data Stores
No flows between external entities
Diagram Zero
CSC Systems Analysis and Design

51. CSC 2202 Systems Analysis and Design
Context Diagram
One Process/System
The system/process being analyzed
Name: Usually a Noun phrase
Show Context Only
Inputs/outputs
External Entities
No Data Stores
No flows between external entities
Diagram Zero
CSC Systems Analysis and Design

52. CSC 2202 Systems Analysis and Design
DFD guidelines
Any data flow leaving a process must be based on data that is input to the process (Outputs must be derivable from inputs).
All data flows are named and the name reflects the data flowing between the processes, sources, and data stores (All elements must be named).
All process have both inputs and outputs.
No physical items
CSC Systems Analysis and Design

53. CSC 2202 Systems Analysis and Design
DFD guidelines
5. All the data needed to perform the process should be input to that process.
6. The process should be independent of any other in the system – each process has its own input and output.
7. Data must move through a process.
8. Different data flows may not merge
CSC Systems Analysis and Design

54. CSC 2202 Systems Analysis and Design
More on DFD guidelines
All DFD diagrams must have a Heading with :
Name and Diagram No. (except for context diagram)
All process bubbles must have name and no.
Conservation of Data Flow Flow Out = Flow In + Amount Stored -applies to Transform bubbles and data stores
CSC Systems Analysis and Design

55. CSC 2202 Systems Analysis and Design
More on DFD guidelines
Avoid infinite sinks i.e. a process with no outgoing dataflows
Avoid spontaneous generation
bubbles i.e. a process without any incoming dataflows
Beware of read-only or write-only data stores
CSC Systems Analysis and Design

56. CSC 2202 Systems Analysis and Design
Data Flow Diagram
Ref:
CSC Systems Analysis and Design

57. Levelling Data Flow Diagrams
DFDs can be drawn in various levels of details using a technique known as levelling, ranging from depicting an entire system’s “big picture” to showing the detailed processing of a single transaction. The entire collection of DFDs is called a levelled set.
Leveling breaks down higher level (parent) DFD into constituent lower level (child) DFDs
CSC Systems Analysis and Design

58. CSC 2202 Systems Analysis and Design
Data Flow Diagrams – Numbering Rules
CSC Systems Analysis and Design

59. Levelling Data Flow Diagrams
How many levels deep in the hierarchy should processes continue to be exploded?
Based on the judgement of the analyst
Some guidelines of when to stop drawing more detailed diagrams are when a process bubble:
-has a single input and output
-performs a single, well-defined function
CSC Systems Analysis and Design

60. Levelling Data Flow Diagrams
How many levels deep in the hierarchy should processes continue to be exploded?
Functional primitive or primitive transform is the name given to each of the lowest level process bubbles
Has an elementary process description(EDP)
Unlikely that all parts partitioned to the same level
CSC Systems Analysis and Design

61. Levelling Data Flow Diagrams
Most investigations will stop at level 2 and it is very unusual to go beyond a level 3 diagram
CSC Systems Analysis and Design

62. Levelling Data Flow Diagrams
CSC Systems Analysis and Design

63. CSC 2202 Systems Analysis and Design
Drawing DFDs
Determine the System boundary
Context Diagram - one circle containing the system name
Draw and label the external entities
Draw the major system inputs and outputs
Diagram 0 and below is more difficult - start with what you know - not at the “Beginning”
Decompose Diagram 0 to lower level diagrams
CSC Systems Analysis and Design

64. Data Dictionary - supporting documentation for DFDs
DFD’s need supporting documentation to define:
The contents of the packets of data in the data flows
the contents of the data stores
the processing that takes place in bubbles that have not been partitioned
CSC Systems Analysis and Design

65. Data Dictionary - supporting documentation for DFDs
4. To add the control functions that are omitted from DFD’s e.g. IF... ELSE ... logic; process performed at the end of each day; etc
5. Data Dictionary is developed in parallel with the DFD
CSC Systems Analysis and Design

66. Data Dictionary - supporting documentation for DFDs
A data dictionary is used to record information about a system (textual and numeric) that cannot be recorded on diagrams
It is a database that supports analysts and designers in the task of analyzing, modeling and designing computer systems
CSC Systems Analysis and Design

67. Data Dictionary - supporting documentation for DFDs
DD may be paper based
Purpose designed DD based on commercial DBMS are now available.
A DD can be considered as a case tool.
CSC Systems Analysis and Design

68. CSC 2202 Systems Analysis and Design
Review questions
Explain the role of data flow diagrams in the systems development process.
Explain the difference between logical and physical data flow diagrams - use an example.
Describe each of the four components of a data flow diagram.
CSC Systems Analysis and Design