Requirements Analysis and Definition

1
Requirements Analysis and Definition

• COMM1B Unit 14

2
Overview

• Systems Analysis Process
• Requirements Definition
• Example of Requirements List
• Functional Requirements
• Non-Functional Requirements
• Example Requirements Catalogue Entry
• Example

3
Systems Analysis Process
4
Main Components of Systems Analysis

• Examine existing system
• document (model) current system - use DFMs,
  entity models etc.
• document problems with existing system
• create catalogue of problems, categorising level
  of problem and providing short description of the
  problem and its impact.

• Consider future system
• document requirements of future system
• create catalogue of requirements, prioritise
  these providing short description of requirement
  and its impact.

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Requirements Definition

• Two types of requirements
• (i) Functional and (ii) Non-functional.
• Both need to be quantifiable/measurable
• Defined in enough detail for decision making.
• The purpose is to find out WHAT is required?
• WHO by?
• WHEN by?
• WHY is it required?
• HOW important is it?
• WHAT measures apply?

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Example of Requirements List

• No. Requirement
• 1 To produce a pre-printed appointment schedule
  for the days patients
• 2 X-ray film tracking mechanism to be introduced
• 3 A facility to produce appointment letters
• 4 To allow direct access to the patient history
  by radiology number and/or NHS number
• .
• 13 Standard maintenance and enquiry facilities to
  be available for all entities
• 14 Produce ad hoc management reports, including
  X-ray films not reported list, Film file weeding
  / culling list.
• 15 Produce standard statistical reports GP
  analysis, Examination analysis, Korner returns
  (for the Department of Health)
• 16 Enquiry responses to be within 10 seconds
• 17 Data access to be kept under security controls
• 18 System to be available 24 hours per day,
  accessible 95-100 of the time.

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Functional Requirements
Describe HOW or HOW WELL or to WHAT LEVEL
something should be done Describe WHAT the system
should do

• 13 Standard maintenance and enquiry facilities to
  be available for all entities
• 14 Produce ad hoc management reports, including
  X-ray films not reported list, Film file weeding
  / culling list.
• 15 Produce standard statistical reports GP
  analysis, Examination analysis, Korner returns
  (for the Department of Health)

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Non-Functional Requirements

• These can be considered as constraints
• Service level requirements
• Access Restrictions
• Security
• Capacity
• Audit, Monitoring and Control

16 Enquiry responses to be within 10
seconds 17 Data access to be kept under specified
security controls 18 System to be available 24
hours per day, accessible 95-100 of the time.
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Example Requirements Catalogue Entry
System College Library Date 12/10/03
Req. ID 07 Priority Medium
Source Front desk Responsibility Chief
Librarian
Functional Requirement To provide on-line access
to query details of overdue loans for a specified
borrower
Non-Functional Requirements Access restricted to
Librarians and Assistants Availability 09.00
-19.00 hrs, Mon - Fri Acceptable response time 3
seconds
Related Requirements 04, 06
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Example

• The example following is for a x-ray service in a
  hospital. It follows through
• looking at current system
• Stating some of the functional requirements
• providing models showing how these can be
  satisfied
• Stating some non functional requirements
• looking at how these can be expressed.

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Logical DFD of the Current System
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Logical Data Model of the Current System
PATIENT
be associated with
Refer to
t
REQUEST
X-RAY
Result in
result
from
APPOINTMENT
result
result
in
in
result
from
result
from
X-RAY FILM
X-RAY REPORT
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Example Functional Requirements

• Example Requirements
• Provide statistics for the X-ray department
  manager, eg.
• report to show appointments actually kept
  between two dates
• An X-ray category is to be stored
• each X-Ray film must belong to only one X-Ray
  category and an X-Ray category may contain one or
  more X-Ray films
• X-Ray films and reports
• an X-Ray report may refer directly to a number of
  X-Ray films and an X-Ray film must be referred
  to directly by at least one X-Ray report

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Logical DFD of the Required System
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Structured English Supporting Appointments Report

• REPEAT
• READ next appointment
• IF Appointment-date is between Beginning-date
  and End-date
• ADD 1 to Total-number-appointments
• IF Appointment-kept-flag Y
• ADD 1 to Total-number-appointments-kept
• ENDIF
• ENDIF
• UNTIL no more appointments
• CALCULATE etc.

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Logical Data Model of the Required System
PATIENT
LDM Supporting the first requirement
be associated with
refer
to
X-RAY
REQUEST
result
in
result
from
X-RAY
APPOINTMENT
CATEGORY
result
result
contain
in
in
result
belong
from
to
result
from
X-RAY FILM
X-RAY REPORT
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Logical Data Model of the Required System
PATIENT
LDM Supporting the second requirement
be associated with
refer
to
X-RAY
REQUEST
result
in
result
from
X-RAY
APPOINTMENT
CATEGORY
result
result
contain
in
in
result
belong
from
to
result
from
directly
refer
X-RAY FILM
X-RAY REPORT
be directly
referred to
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Example Non-Functional Requirements

• Typical Issues considered
• Service level requirements
• Access restrictions
• Security
• Monitoring
• Audit and control
• Constraints

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Summary

• Meet user and business requirements
• Guidelines not exhaustive
• Reliance on fact-finding skills
• Iterative process

Taken from NCC training 1991