Requirements Analysis and

Specification
 Many projects fail:
 because they start implementing
the system without determining
whether they are building what
the customer really wants.

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Requirements Analysis and
Specification
 Goals of requirements analysis and
specification phase:
 fully understand the user requirements
 remove inconsistencies, anomalies,
etc. from requirements
 document requirements properly in an
SRS document

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Requirements Analysis and
Specification
 Consists of two distinct
activities:
 Requirements Gathering and
Analysis
 Specification

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Requirements Analysis and
Specification
 The person who undertakes requirements
analysis and specification:
 known as systems analyst:
 collects data pertaining to the product
 analyzes collected data:
 to understand what exactly needs to be done.
 writes the Software Requirements
Specification (SRS) document.

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Requirements Analysis and
Specification
 Final output of this phase:
 Software Requirements
Specification (SRS) Document.
 The SRS document is reviewed by
the customer.
 reviewed SRS document forms the
basis of all future development
activities.

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 Requirements Gathering

 Analyst gathers requirements

through:
 observation of existing systems,
 studying existing procedures,
 discussion with the customer and end-
users,
 analysis of what needs to be done, etc.

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Requirements Gathering
(CONT.)

 In the absence of a working

system,
 lot of imagination and creativity are
required.
 Interacting with the customer to
gather relevant data:
 requires a lot of experience.

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Requirements Gathering
(CONT.)

 Some desirable attributes of

a good system analyst:
 Good interaction skills,
 imagination and creativity,
 experience.

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Analysis of the Gathered
Requirements
 After gathering all the requirements:
 analyze it:
 Clearly understand the user requirements,
 Detect inconsistencies, ambiguities, and
incompleteness.
 Incompleteness and inconsistencies:
 resolved through further discussions with
the end-users and the customers.

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Inconsistent requirement
 Some part of the requirement:
 contradicts with some other part.
 Example:
 One customer says turn off heater and
open water shower when temperature >
100 C
 Another customer says turn off heater and
turn ON cooler when temperature > 100 C

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Incomplete requirement
 Some requirements have been
omitted:
 due to oversight.
 Example:
 The analyst has not recorded:
when temperature falls below 90 C
 heater should be turned ON
 water shower turned OFF.

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Analysis of the Gathered
Requirements (CONT.)

 Requirements analysis involves:

 obtaining a clear, in-depth
understanding of the product to
be developed,
 remove all ambiguities and
inconsistencies.

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Analysis of the Gathered
Requirements (CONT.)

 Several things about the project should

be clearly understood by the analyst:
 What is the problem?
 Why is it important to solve the problem?
 What are the possible solutions to the
problem?
 What complexities might arise while solving
the problem?

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Analysis of the Gathered
Requirements (CONT.)

 After collecting all data regarding

the system to be developed,
 remove all inconsistencies and
anomalies from the requirements,
 systematically organize requirements
into a Software Requirements
Specification (SRS) document.

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Software Requirements
Specification

 Main aim of requirements

specification:
 systematically organize the
requirements arrived during
requirements analysis
 document requirements properly.

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Software Requirements
Specification

 The SRS document is useful in

various contexts:
 statement of user needs
 contract document
 reference document
 definition for implementation

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Software Requirements Specification: A
Contract Document

 Requirements document is a reference

document.
 SRS document is a contract between the
development team and the customer.
 Once the SRS document is approved by the
customer,
 any subsequent controversies are settled by
referring the SRS document.

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Software Requirements Specification:
A Contract Document

 Once customer agrees to the SRS

document:
 development team starts to develop the product
according to the requirements recorded in the
SRS document.
 The final product will be acceptable to the
customer:
 as long as it satisfies all the requirements
recorded in the SRS document.
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SRS Document (CONT.)

 The SRS document is known as black-box

specification:
 the system is considered as a black box whose
internal details are not known.
 only its visible external (i.e. input/output)
behaviour is documented.
Input Data Output Data
S

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SRS Document (CONT.)

 SRS document concentrates on:

 what needs to be done
 carefully avoids the solution (“how to do”)
aspects.
 The SRS document serves as a contract
 between development team and the customer.
 Should be carefully written

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SRS Document (CONT.)

 The requirements at this stage:

 written using end-user terminology.
 later a formal requirement
specification may be developed
from it.

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Properties of a good SRS
document
 It should be concise
 and at the same time should not be
ambiguous.
 It should specify what the system must do
 and not say how to do it.
 Easy to change.,
 i.e. it should be well-structured.
 It should be consistent.
 It should be complete.

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Properties of a good SRS
document (cont...)

 It should be traceable
 you should be able to trace which part of the
specification corresponds to which part of the
design and code, etc and vice versa.
 It should be verifiable
 e.g. “system should be user friendly” is not verifiable

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SRS Document (CONT.)

 SRS document, normally

contains three important parts:
 functional requirements,
 Non functional requirements,
 constraints on the system.

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SRS Document (CONT.)

 It is desirable to consider every

system:
 performing a set of functions {fi}.
 Each function fi considered as:
 transforming a set of input data to
corresponding output data.
Input Data Output Data
fi

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Example: Functional
Requirement
 F1: Search Book
 Input:
 an author’s name:
 Output:
 details of the author’s books and the
locations of these books in the library.
Author Name Book Details
f1

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Functional Requirements

 Functional requirements describe:

 A set of high-level requirements
 Each high-level requirement:
 takes in some data from the user
 outputs some data to the user
 Each high-level requirement:
 might consist of a set of identifiable
functions

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Functional Requirements

 For each high-level requirement:

 every function is described in terms of
 input data set
 output data set
 processing required to obtain the output
data set from the input data set

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29
Nonfunctional
Requirements
 In addition to the obvious features and functions that you will
provide in your system, there are other requirements that don't
actually DO anything, but are important characteristics
nevertheless. These are called "non-functional requirements" or
sometimes "Quality Attributes." 

 For example, attributes such as performance, security, usability,

compatibility. aren't a "feature" of the system, but are a required
characteristic.

 You can't write a specific line of code to implement them, rather

they are "emergent" properties that arise from the entire solution.  

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Non functional
Requirements
 Non functional requirements include:
 Reliability: the extent to which it works as and
when needed.
 Performance: speed and throughput.
 Security: accessible and usable only in
authorized ways by authorized users.
 Maintainability: speed and reliability of
updating and/or correcting production products.

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Non functional
Requirements
Portability: ability and ease of using
the solution in different configurations
or environments.
Efficiency: taking minimal time,
effort, resources or cost to create, or
operating a solution.
Safety: not causing harm, injury or
damage.
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Constraints
 Constraints describe things that the
system should or should not do.
 For example,
 standards compliance
 how fast the system can produce results
• so that it does not overload another
system to which it supplies data, etc.

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Examples of constraints

 Hardware to be used,
 Operating system
 or DBMS to be used
 Capabilities of I/O devices
 Standards compliance
 Data representations
 by the interfaced system

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Organization of the SRS
Document
 Introduction.
 Functional Requirements
 Nonfunctional Requirements
 External interface requirements
 Performance requirements
 Constraints

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Example Functional
Requirements
 List all functional requirements
 with proper numbering.
 Req. 1:
 Once the user selects the “search” option,
 he is asked to enter the key words.
 The system should output details of all
books
 whose title or author name matches any of
the key words entered.
 Details include: Title, Author Name, Publisher
name, Year of Publication, ISBN Number,
Catalog Number, Location in the Library.

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Example Functional Requirements

 Req. 2:
 When the “renew” option is selected,
 the user is asked to enter his membership
number and password.
 After password validation,
 the list of the books borrowed by him are
displayed.
 The user can renew any of the books:
 by clicking in the corresponding renew box.

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Req. 1:
 R.1.1:
 Input: “search” option,
 Output: user prompted to enter the key words.
 R1.2:
 Input: key words
 Output: Details of all books whose title or author
name matches any of the key words.
 Details include: Title, Author Name, Publisher name, Year
of Publication, ISBN Number, Catalog Number, Location in
the Library.
 Processing: Search the book list for the keywords

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Req. 2:
 R2.1:
 Input: “renew” option selected,
 Output: user prompted to enter his
membership number and password.
 R2.2:
 Input: membership number and password
 Output:
 list of the books borrowed by user are
displayed. User prompted to enter books to be
renewed or
 user informed about bad password
 Processing: Password validation, search
books issued to the user from borrower list
and display.
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Req. 2:

 R2.3:
 Input: user choice for renewal of the
books issued to him through mouse clicks
in the corresponding renew box.
 Output: Confirmation of the books
renewed
 Processing: Renew the books selected by
the in the borrower list.
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Examples of Bad SRS
Documents
 Unstructured Specifications:
 Narrative essay --- one of the worst
types of specification document:
 Difficult to change,
 difficult to be precise,
 difficult to be unambiguous,
 scope for contradictions, etc.
 Forward References:
 References to aspects of problem
 defined only later on in the text.
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Examples of Bad SRS
Documents
 Overspecification:
 Addressing “how to” aspects
 For example, “Library member names should be
stored in a sorted descending order”
 Overspecification restricts the solution space for
the designer.
 Contradictions:
 Contradictions might arise
 if the same thing described at several places in different
ways.

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Summary
 Requirements analysis and specification
 an important phase of software
development:
 any error in this phase would affect all
subsequent phases of development.
 Consists of two different activities:
 Requirements gathering and analysis
 Requirements specification

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Summary
 The aims of requirements analysis:
 Gather all user requirements
 Clearly understand exact user requirements
 Remove inconsistencies and incompleteness.
 The goal of specification:
 systematically organize requirements
 document the requirements in an SRS
document.

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Summary
 Main components of SRS document:
 functional requirements
 Non functional requirements
 constraints

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