Object oriented analysis &design - requirement analysis

Object
Oriented

Analysis &design
Requirement Analysis

References :
OOAD by timothy.
OOAD by tulsiram sule.(techmax)

Presentation by Abhilasha Lahigude

Requirements
 What
o

o

is a requirement?

Definition:
A requirement is a statement describes either
1) an aspect of what the proposed system must do,
or 2) a constraint on the system’s development. In
either case, it must contribute in some way towards
adequately solving the customer’s problem; the set
of requirements as a whole represents a negotiated
agreement among all stakeholders.

i.e. requirement is a relatively short and concise
piece of information/statement
about what the projected system will do and how
the system will be developed
and all the stakeholders have agreed on it.

Requirement
o

Let us dissect this definition in order to better understand it:
• A requirement is a statement…: this means that each requirement is a
relatively short and concise piece of information, expressed as a fact. It
can be written as a sentence or can be expressed using some kind of
diagram. We will call a collection of requirements a requirements
document.
• …an aspect of what the proposed system must do…: most
requirements say something about the tasks the system is supposed to
accomplish. They do not describe the domain.
• …a constraint on the system’s development…: requirements often
specify the quality levels required. They may also specify details such as
the programming language to be used if this is truly important to the
customer. They should, however, avoid discussing incidental aspects of
the design.
• …contribute … towards adequately solving the customer’s problem: a
requirement should only be present if it helps solve the customer’s
problem – as we discussed in Chapter 1, this is what software
engineering is all about.
• …a negotiated agreement among all stakeholders…: a statement
about the system should not be declared to be an official requirement
until all the stakeholders (users, customers, developers and their
management) have reviewed it, have negotiated any needed
changes, and have agreed that it is valid

Types of requirements

 Requirements

major types:
1.
2.

can be divided into two

Functional.
non-functional(quality, performance,
design, platform and process).

Functional Requirements
 Functional

requirements describe what the system
should do; i.e., they describe the services provided
for the users and for other systems.
 The functional requirements discuss the functionality
required by the users from the system.
 functional
1)
2)

requirements should include :

everything that a user of the system would need to
know regarding what the system does, and
everything that would concern any other system that
has to interface to this system. Details that go any
deeper into how the requirements are implemented
should be left out.

Functional Requirements


The functional requirements can be further categorized as follows:
o

What inputs the system should accept, and under what conditions. This
includes data and commands both from the users and from other systems.

o

What outputs the system should produce, and under what conditions.

Outputs can be to the screen or printed. They can also be transmitted to other systems, such
as special I/O devices, clients or servers.
o

What data the system should store that other systems might use. This is

really a special kind of output that will eventually become an input to other systems. Data

(e.g. the specifics of a file format
used to temporarily back up some data) can be ignored until the design stage.
What computations the system should perform. The computations should be
which is stored for the exclusive use of this system

o

described at a level that all the readers can understand. For example, you would describe
a sorting process by saying that the result is to be ordered in ascending sequence
according to the account number. You would not normally specify the particular algorithm
to be used.
o

The timing and synchronization of the above. Not all systems involve timing

and synchronization – this category of functional requirements is of most importance in hard

(e.g.
telecommunications systems, systems that control power plants or
factories, and systems that run automobiles and airplanes).
real-time systems that do such things as control hardware devices

Non-functional
Requirements
A

Non-functional requirement is a statement of how
a system must behave; it is a constraint upon
system’s behaviour.
 Non-functional requirements can be categorized
as:
o
o
o

o
o

Quality constraint.
Performance constraint.
Design constraint.
Environmental / platform constraint.
Process constraint.

Non-functional
Requirements
Quality Constraint:
Quality constraints reflects the quality attributes. These quality
requirements constrain the design to meet specified levels of
quality.
Following are some quality attributes:
 Maintainability and Enhancement:In order to ensure that the
system can be adapted in the future, you should describe
changes that are anticipated for subsequent releases. This
constrains design and improves quality without adding explicit
new functional requirements.
 Reusability: Reusability is the likelihood a segment of source
code that can be used again to add new functionalities with
slight or no modification. Reusability reduces implementation
time as reusable model is already tested.
 Reliability: Reliability is specified by using mean time to failure.
It is the ability of a system to perform its functions under stated
conditions for a specified period of time.

Non-functional
Requirements
Performance constraints:
Response time: Response time is time system take to
compute the result.
Low response time is desirable.
Throughput: It is number of computation or transactions
per unit time.
Some systems take long time for processing or Some
systems are continually responding to client , it is
necessary to consider throughput.
Utilization: Utilization is resources consumed by the
system.
Utilization of resources such as memory or network
bandwidth are specified.
E.g. system should not use more than 20MBPS of
bandwidth.

Non-functional
Requirements
Design constraints:
 Availability:

Availability measures the amount of
time that a server is running and available to
respond to users.
E.g. System should not down for more than 5
minutes.
 Recovery from failure: If the hardware or software
crashes, or the power fails, then the system will be
able to recover within a certain amount of time,
and with a certain minimal loss of data.

Non-functional
Requirements
Environmental/Platform constraints:
Platform:

Platform specifies the hardware and
operating system used for developing system.
E.g. Linux operating system with 2GB RAM.
Technology to be used: It signifies the programming
language (framework) used to develop a system.
Sometimes client places constraint on programming
language to be used for developing system.
E.g. System should be developed by using java
language.

Non-functional
Requirements
Process constraints:
 Development

process to be used: In order to ensure
quality, some requirements documents specify that
certain processes be followed;
E.g. particular approaches to testing.
The details of the process should not be included in the requirements; instead a reference
should be made to other documents that describe the process.

 Cost

and delivery date.

Object oriented analysis &design - requirement analysis

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