requirements analysis and design

Requirements Analysis
and
Design

Requirement
• A thing that is needed or wanted.
• A thing that is compulsory; a necessary condition.

Types of Requirements
• Functional Requirements
• Non Functional Requirements (NFRs)
– Performance
– Security
– Logging
– Reliability

Characteristics of Good Requirements
• Correct
• Clear
• Understandable
• Unambiguous
• Testable (Verifiable)
• Feasible
• Independent
• Atomic
• Necessary
• Implementation-free
• Consistent
• Complete
• Non-redundant

Requirements
Engineering Tasks

The Problems with our Requirements Practices
• We have trouble understanding
the requirements that we do
acquire from the customer
• We often record requirements in
a disorganized manner
• We spend far too little time
verifying what we do record
• We allow change to control us,
rather than establishing
mechanisms to control change
• Most importantly, we fail to
establish a solid foundation for
the system or software that the
user wants built

The Problems with our Requirements Practices
• Many software developers argue that
– Building software is so compelling that we want to jump right in
(before having a clear understanding of what is needed)
– Things will become clear as we build the software
– Project stakeholders will be able to better understand what they
need only after examining early iterations of the software
– Things change so rapidly that requirements engineering is a waste
of time
– The bottom line is producing a working program and that all else is
secondary

A Solution: Requirements Engineering
• Begins during the communication activity and continues into the
modeling activity
• Builds a bridge from the system requirements into software design
and construction
• Allows the requirements engineer to examine
– the context of the software work to be performed
– the specific needs that design and construction must address
– the priorities that guide the order in which work is to be completed
– the information, function, and behavior that will have a profound impact on
the resultant design

Requirements Engineering Tasks
• Seven distinct tasks
– Inception
– Elicitation
– Elaboration
– Negotiation
– Specification
– Validation
– Requirements Management
• Some of these tasks may occur in parallel and all are adapted to
the needs of the project
• All strive to define what the customer wants
• All serve to establish a solid foundation for the design and
construction of the software

Requirements
Management
Validation
Inception
Elicitation
Elaboration
Negotiation
Specification

Inception Task
• During inception, the requirements engineer asks a set of questions to
establish…
– A basic understanding of the problem
– The people who want a solution
– The nature of the solution that is desired
– The effectiveness of preliminary communication and collaboration
between the customer and the developer
• Through these questions, the requirements engineer needs to…
– Identify the stakeholders
– Recognize multiple viewpoints
– Work toward collaboration
– Break the ice and initiate the communication

Questions Asked..First Set of questions Next Set of Questions Final Set of questions
These questions focus on the
customer, other stakeholders,
the overall goals, and the
benefits
These questions enable the
requirements engineer to gain a
better understanding of the
problem and allow the customer to
voice his or her perceptions about
a solution
These questions focus on
the effectiveness of the
communication activity itself
• Who is behind the request
for this work?
• Who will use the solution?
• What will be the economic
benefit of a successful
solution?
• Is there another source for
the solution that you need?
• How would you characterize
"good" output that would be
generated by a successful
solution?
• What problem(s) will this
solution address?
• Can you show me (or describe)
the business environment in
which the solution will be used?
• Will special performance issues
or constraints affect the way the
solution is approached?
• Are you the right person
to answer these
questions? Are your
answers "official"?
• Are my questions
relevant to the problem
that you have?
• Am I asking too many
questions?
• Can anyone else provide
additional information?
• Should I be asking you
anything else?

Elicitation Task
• Eliciting requirements is difficult because of
– Problems of scope in identifying the boundaries of the system or
specifying too much technical detail rather than overall system
objectives
– Problems of understanding what is wanted, what the problem
domain is, and what the computing environment can handle
(Information that is believed to be "obvious" is often omitted)
– Problems of volatility because the requirements change over time
• Elicitation may be accomplished through two activities
– Collaborative requirements gathering
– Quality function deployment

Elicitation Work Products
• A statement of need and feasibility
• A bounded statement of scope for the system or product
• A list of customers, users, and other stakeholders who
participated in requirements elicitation
• A description of the system's technical environment
• A list of requirements (organized by function) and the domain
constraints that apply to each
• A set of preliminary usage scenarios (in the form of use cases)
that provide insight into the use of the system or product under
different operating conditions
• Any prototypes developed to better define requirements
The work products will vary depending on the system, but should
include one or more of the following items

Collaborative Requirements Gathering
• Meetings are conducted and attended by both software
engineers, customers, and other interested stakeholders
• Rules for preparation and participation are established
• An agenda is suggested that is formal enough to cover all
important points but informal enough to encourage the free flow
of ideas
• A "facilitator" (customer, developer, or outsider) controls the
meeting
• A "definition mechanism" is used such as work sheets, flip
charts, wall stickers, electronic bulletin board, chat room, or
some other virtual forum
• The goal is to identify the problem, propose elements of the
solution, negotiate different approaches, and specify a
preliminary set of solution requirements

Quality Function Deployment
• This is a technique that translates the needs of the customer
into technical requirements for software
• It emphasizes an understanding of what is valuable to the
customer and then deploys these values throughout the
engineering process through functions, information, and tasks
• It identifies three types of requirements
– Normal requirements: These requirements are the objectives and
goals stated for a product or system during meetings with the
customer
– Expected requirements: These requirements are implicit to the
product or system and may be so fundamental that the customer
does not explicitly state them
– Exciting requirements: These requirements are for features that go
beyond the customer's expectations and prove to be very satisfying
when present

Elaboration Task
• During elaboration, the software engineer takes the information
obtained during inception and elicitation and begins to expand
and refine it
• Elaboration focuses on developing a refined technical model of
software functions, features, and constraints
• It is an analysis modeling task
– Use cases are developed
– Domain classes are identified along with their attributes and
relationships
– State machine diagrams are used to capture the life on an object
• The end result is an analysis model that defines the functional,
informational, and behavioral domains of the problem

Developing Use Cases
• Already Done
(Refer to Use Case diag slides)

Negotiation Task
• During negotiation, the software engineer
reconciles the conflicts between what the
customer wants and what can be achieved
given limited business resources
• Requirements are ranked (i.e., prioritized)
by the customers, users, and other
stakeholders
• Risks associated with each requirement
are identified and analyzed
• Rough guesses of development effort are
made and used to assess the impact of
each requirement on project cost and
delivery time
• Using an iterative approach, requirements
are eliminated, combined and/or modified
so that each party achieves some measure
of satisfaction

Specification Task
• A specification is the final work product produced by the requirements
engineer
• It is normally in the form of a software requirements specification(SRS)
• It serves as the foundation for subsequent software engineering activities
• It describes the function and performance of a computer-based system and
the constraints that will govern its development
• It formalizes the informational, functional, and behavioral requirements of
the proposed software in both a graphical and textual format

Software Requirements
Specification
Lab work on SRS ( Software Requirement Specification)

Validation Task
• During validation, the work products produced as a result of requirements engineering are
assessed for quality
• The specification is examined to ensure that
– all software requirements have been stated unambiguously
– inconsistencies, omissions, and errors have been detected and corrected
– the work products conform to the standards established for the process, the project, and the product
• The formal technical review serves as the primary requirements validation mechanism
– Members include software engineers, customers, users, and other stakeholders
• Do any requirements conflict with other requirements?
• Is each requirement achievable in the technical environment that will house the system or
product?
• Is each requirement testable, once implemented?
– Approaches: Demonstration, actual test, analysis, or inspection
• Does the requirements model properly reflect the information, function, and behavior of the
system to be built?
• Has the requirements model been “partitioned” in a way that exposes progressively more
detailed information about the system?

Questions to ask when Validating Requirements
• Is each requirement consistent with the overall objective for the
system/product?
• Have all requirements been specified at the proper level of
abstraction? That is, do some requirements provide a level of
technical detail that is inappropriate at this stage?
• Is the requirement really necessary or does it represent an add-
on feature that may not be essential to the objective of the
system?
• Is each requirement bounded and unambiguous?
• Does each requirement have attribution? That is, is a source
(generally, a specific individual) noted for each requirement?

Requirements Management Task
• During requirements management, the
project team performs a set of activities to
identify, control, and track requirements
and changes to the requirements at any
time as the project proceeds
• Each requirement is assigned a unique
identifier
• The requirements are then placed into one
or more traceability tables
• These tables may be stored in a database
that relate features, sources,
dependencies, subsystems, and interfaces
to the requirements
• A requirements traceability table is also
placed at the end of the software
requirements specification

Requirements Analysis
Modeling

Goals of Analysis Modeling
• Provides the first technical representation of a system
• Is easy to understand and maintain
• Deals with the problem of size by partitioning the system
• Uses graphics whenever possible
• Differentiates between essential information versus
implementation information
• Helps in the tracking and evaluation of interfaces
• Provides tools other than narrative text to describe software
logic and policy

A Set of Models
• Flow-oriented modeling – provides an indication of how data
objects are transformed by a set of processing functions
• Scenario-based modeling – represents the system from the
user's point of view
• Class-based modeling – defines objects, attributes, and
relationships
• Behavioral modeling – depicts the states of the classes and
the impact of events on these states

Overall Objectives
• Three primary objectives
– To describe what the customer requires
– To establish a basis for the creation of a software design
– To define a set of requirements that can be validated once the
software is built
• All elements of an analysis model are directly traceable to parts
of the design model, and some parts overlap

Purpose
• Specifies the software's operational characteristics
• Indicates the software's interfaces with other system elements
• Establishes constraints that the software must meet
• Provides the software designer with a representation of
information, function, and behavior
– This is later translated into architectural, interface, class/data and
component-level designs
• Provides the developer and customer with the means to assess
quality once the software is built

Analysis Rules of Thumb
• The analysis model should focus on requirements that are visible within
the problem or business domain
– The level of abstraction should be relatively high
• Each element of the analysis model should add to an overall
understanding of software requirements and provide insight into the
following
– Information domain, function, and behavior of the system
• The model should delay the consideration of infrastructure and other
non-functional models until the design phase
– First complete the analysis of the problem domain
• The model should minimize coupling throughout the system
– Reduce the level of interconnectedness among functions and classes
• The model should provide value to all stakeholders
• The model should be kept as simple as can be

Domain Analysis
• Definition
– The identification, analysis, and specification of common, reusable
capabilities within a specific application domain
– Do this in terms of common objects, classes, subassemblies, and
frameworks
• Sources of domain knowledge
– Technical literature
– Existing applications
– Customer surveys and expert advice
– Current/future requirements
• Outcome of domain analysis
– Class taxonomies
– Reuse standards
– Functional and behavioral models
– Domain languages

Analysis Modeling Approaches
• Structured analysis
– Considers data and the processes that transform the data as
separate entities
– Data is modeled in terms of only attributes and relationships (but no
operations)
– Processes are modeled to show the 1) input data, 2) the
transformation that occurs on that data, and 3) the resulting output
data
• Object-oriented analysis
– Focuses on the definition of classes and the manner in which they
collaborate with one another to fulfill customer requirements

Elements of the Analysis Model

Data Modeling
• Data Flow Diagram
Already done refer to DFD slides

Scenario Based Modeling: Use Case Diagram
• Use Case Diagram ( already done refer to use case slides)
• Activity Diagram (already done refer to Activity Diagram slides)

Class Based Modeling
• Refer to Object Oriented
Concepts slides and Class
Diagram slide

Behavioral Modeling :State Diagram
• State Diagram ( already done Refer to state diagram
slides)

Summary:
Elements of the Analysis Model
Use case text
Use case diagrams
Activity diagrams
Swim lane diagrams
Scenario-based
modeling
Class diagrams
Analysis packages
CRC models
Collaboration diagrams
Class-based
modeling
Data flow diagrams
Control-flow diagrams
Processing narratives
Flow-oriented
modeling
State diagrams
Sequence diagrams
Behavioral
modeling
Structured AnalysisObject-oriented Analysis

Purpose of Design
• Design is where customer requirements, business needs, and technical considerations all come
together in the formulation of a product or system
• The design model provides detail about the software data structures, architecture, interfaces,
and components
• The design model can be assessed for quality and be improved before code is generated and
tests are conducted
– Does the design contain errors, inconsistencies, or omissions?
– Are there better design alternatives?
– Can the design be implemented within the constraints, schedule, and cost that have been established?
• A designer must practice diversification and convergence
– The designer selects from design components, component solutions, and knowledge available through
catalogueses, textbooks, and experience
– The designer then chooses the elements from this collection that meet the requirements defined by
requirements engineering and analysis modeling
– Convergence occurs as alternatives are considered and rejected until one particular configuration of
components is chosen
• Software design is an iterative process through which requirements are translated into a
blueprint for constructing the software
– Design begins at a high level of abstraction that can be directly traced back to the data, functional, and
behavioral requirements
– As design iteration occurs, subsequent refinement leads to design representations at much lower levels
of abstraction

From Analysis Model to Design Model
• Each element of the analysis model provides information that is necessary
to create the four design models
– The data/class design transforms analysis classes into design classes along with
the data structures required to implement the software
– The architectural design defines the relationship between major structural
elements of the software; architectural styles and design patterns help achieve
the requirements defined for the system
– The interface design describes how the software communicates with systems
that interoperate with it and with humans that use it
– The component-level design transforms structural elements of the software
architecture into a procedural description of software components

51
From Analysis Model to
Design Model (continued)
Data/Class Design
(Class-based model, Behavioral model)
Architectural Design
(Class-based model, Flow-oriented model)
Interface Design
(Scenario-based model, Flow-oriented model
Behavioral model)
Component-level Design
(Class-based model, Flow-oriented model
Behavioral model)

Task Set for Software Design
1) Examine the information domain model and design appropriate data structures for data objects
and their attributes
2) Using the analysis model, select an architectural style (and design patterns) that are
appropriate for the software
3) Partition the analysis model into design subsystems and allocate these subsystems within the
architecture
a) Design the subsystem interfaces
b) Allocate analysis classes or functions to each subsystem
4) Create a set of design classes or components
a) Translate each analysis class description into a design class
b) Check each design class against design criteria; consider inheritance issues
c) Define methods associated with each design class
d) Evaluate and select design patterns for a design class or subsystem
5) Design any interface required with external systems or devices
6) Design the user interface
7) Conduct component-level design
a) Specify all algorithms at a relatively low level of abstraction
b) Refine the interface of each component
c) Define component-level data structures
d) Review each component and correct all errors uncovered
5) Develop a deployment model
 Show a physical layout of the system, revealing which components will be located where in the
physical computing environment

Quality's Role
• The importance of design is quality
• Design is the place where quality is fostered
– Provides representations of software that can be assessed for quality
– Accurately translates a customer's requirements into a finished software
product or system
– Serves as the foundation for all software engineering activities that follow
• Without design, we risk building an unstable system that
– Will fail when small changes are made
– May be difficult to test
– Cannot be assessed for quality later in the software process when time is
short and most of the budget has been spent
• The quality of the design is assessed through a series of formal
technical reviews or design walkthroughs

Goals of a Good Design
• The design must implement all of the explicit requirements
contained in the analysis model
– It must also accommodate all of the implicit requirements desired
by the customer
• The design must be a readable and understandable guide for
those who generate code, and for those who test and support
the software
• The design should provide a complete picture of the software,
addressing the data, functional, and behavioral domains from an
implementation perspective
"Writing a clever piece of code that works is one thing; designing something
that can support a long-lasting business is quite another."

Design Quality Guidelines
1) A design should exhibit an architecture that
a) Has been created using recognizable architectural styles or patterns
b) Is composed of components that exhibit good design characteristics
c) Can be implemented in an evolutionary fashion, thereby facilitating implementation and
testing
2) A design should be modular; that is, the software should be logically partitioned
into elements or subsystems
3) A design should contain distinct representations of data, architecture, interfaces,
and components
4) A design should lead to data structures that are appropriate for the classes to be
implemented and are drawn from recognizable data patterns
5) A design should lead to components that exhibit independent functional
characteristics
6) A design should lead to interfaces that reduce the complexity of connections
between components and with the external environment
7) A design should be derived using a repeatable method that is driven by
information obtained during software requirements analysis
8) A design should be represented using a notation that effectively communicates its
meaning

Design Concepts
Already done in object oriented concepts : refer to ppt of
oo-concepts

The Design Model
Data/Class Design
Interface Design

Process Dimension (Progression)
AbstractionDimension
Data/Class
Elements
Interface
Elements
Architectural
Elements
Component-level
Elements
Deployment-level
Elements
Dimensions of the Design Model
Analysis model
Design model
Low
High

Introduction
• The design model can be viewed in two different dimensions
– (Horizontally) The process dimension indicates the evolution of the parts of the
design model as each design task is executed
– (Vertically) The abstraction dimension represents the level of detail as each
element of the analysis model is transformed into the design model and then
iteratively refined
• Elements of the design model use many of the same UML diagrams used in
the analysis model
– The diagrams are refined and elaborated as part of the design
– More implementation-specific detail is provided
– Emphasis is placed on
• Architectural structure and style
• Interfaces between components and the outside world
• Components that reside within the architecture

Introduction (continued)
• Design model elements are not always developed in a
sequential fashion
– Preliminary architectural design sets the stage
– It is followed by interface design and component-level design,
which often occur in parallel
• The design model has the following layered elements
– Data/class design
– Architectural design
– Interface design
– Component-level design
• A fifth element that follows all of
the others is deployment-level design
Data/Class Design
Interface Design

Design Elements
• Data/class design
– Creates a model of data and objects that is represented at a high level
of abstraction
• Architectural design
– Depicts the overall layout of the software
• Interface design
– Tells how information flows into and out of the system and how it is
communicated among the components defined as part of the
architecture
– Includes the user interface, external interfaces, and internal interfaces
• Component-level design elements
– Describes the internal detail of each software component by way of data
structure definitions, algorithms, and interface specifications
• Deployment-level design elements
– Indicates how software functionality and subsystems will be allocated
within the physical computing environment that will support the software

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