SE - Lecture 2 - SW Devl Process.pptx

ITS 66404
Principles of Software
Engineering
Nur Haifa
Chapter 2- Software
Development
Process

Agenda
✧ Components Involved
✧ Software process models
▪ Waterfall Model/SDLC
▪ Incremental Process
▪ Evolutionary Process
▪ Concurrent models
✧ Process activities
✧ Coping with change
✧ Process improvement
Chapter 1 – Intro to Software Engineering 2

Components Involved
Chapter 2 Software Processes 3

Components of Software Engineering
An agreed, common language
used to communicate all
aspects of the system, from
requirements to final design.
EXAMPLE: UML Diagrams
NOTATIONS
A framework for the tasks required to
build high-quality software.
EXAMPLE: RUP, XP.
PROCESSES
The actual software product or
system built and put into operation
EXAMPLE: eCOMMERCE
SYSTEMS, Mobile App, Batch
Systems
PRODUCT
Tools to make working through the
process less difficult for all involved
EXAMPLE: Visual Paradigm,
Eclipse, Poseidon, Draw.io
TOOLS

Engineering involves processes
+ Small programs (<10,000 lines) can be implemented easily by
one person
+ Larger systems need a more systematic approach
+ We distinguish between the product (what we are making)
and the process (how we make it)
+ Engineering deals explicitly with process issues
5

Software Development Life Cycle
SDLC has several clearly defined phases
1. Requirements gathering
Finding out what the user wants
2. Systems analysis
Understanding/documenting requirements
3. Design
Planning a possible solution
4. Implementation
Building a solution
5. Testing
Ensuring it meets requirements
6. Deployment and Maintenance
Requirements gathering and systems analysis are performed iteratively.
Design/Implementation/Testing are done sequentially.
6

Other parts of the life cycle
Other aspects of developing software
Feasibility analysis
Is it technically possible to build the system?
Does the company have the ability to build it
People
Skills
Finance
Time
7

Project scoping
Deals with putting limits on how much you want to create/clearly specifying what
you want to achieve.
You may decide to leave network play out of a game.
An accounting package may be limited to one database back-end.
A music player may only play songs encoded in MP3 format
The product may have to be developed with a budget no greater than
$400,000
The product may have to be created within 12 months
8

Project management
Estimating development time
Ensuring people are used effectively
Ensuring good communication and a healthy work environment
Managing budgets
Training and handover
Maintenance
These issues won’t be covered in this course.
9

The stages of software development
We'll look at each of these in turn.
10

Requirements
Requirements are things that the user wants
the system to do.
They are grouped into
Functional - behaviours we expect the system to
have
Non Functional - other features to which the system
must conform.
Can be extremely hard to capture
Hard to document
Hard to get from the user
11

Analysis
The requirements are analysed and
documented in detail - we attempt to
have an understanding of what the
requirements mean, and search for all
possible consequences.
Sometimes requirements are given to you.
You have to understand the terms used
Detail the relationships between items
Understand the order in which processes must
occur
Sometimes you have to create the
requirements
Interviewing clients
Examining existing systems 12

Design
Analysis is concerned with what the
client wants, and what the client
understands/cares about.
Design deals with how the system will
be implemented. You might have
to choose...
Database
Implementation Language
How to organise the implementation
Hardware requirements
Design stage usually ends with (at
least) class descriptions/methods
13

Implementation
Each class is implemented according to
the design document.
Each class is tested to ensure it
matches the class’s expected
behaviour.
Producing correct output given correct input.
Meeting timing requirements
The classes are integrated to produce
the final system.
14

Testing
The final system is tested to see if it
meets the original requirements.
The components of the system are
pieced together, and the
interaction between them is tested.
User manuals/procedures are tested
Backup procedures are tested.
15

The software process
✧ A structured set of activities required to develop a
software system.
✧ Many different software processes but all involve:
▪ Specification – defining what the system should do;
▪ Design and implementation – defining the organization of the system and
implementing the system;
▪ Validation – checking that it does what the customer wants;
▪ Evolution – changing the system in response to changing customer needs.
✧ A software process model is an abstract representation of a
process. It presents a description of a process from some
particular perspective. Chapter 2 Software Processes 16

Software process descriptions
✧ When we describe and discuss processes, we usually talk
about the activities in these processes such as specifying a
data model, designing a user interface, etc. and the
ordering of these activities.
✧ Process descriptions may also include:
▪ Products, which are the outcomes of a process activity;
▪ Roles, which reflect the responsibilities of the people involved in the
process;
▪ Pre- and post-conditions, which are statements that are true before and
after a process activity has been enacted or a product produced.

Software process models

Plan-driven and agile processes
✧ Plan-driven processes are processes where all of the process
activities are planned in advance and progress is measured
against this plan.
✧ In agile processes, planning is incremental and it is easier to
change the process to reflect changing customer requirements.
✧ In practice, most practical processes include elements of both
plan-driven and agile approaches.
✧ There are no right or wrong software processes.

Software process models
✧ The waterfall model
▪ Plan-driven model. Separate and distinct phases of specification and development.
✧ Incremental development
▪ Specification, development and validation are interleaved. May be plan-driven or agile.
✧ Integration and configuration
▪ The system is assembled from existing configurable components. May be plan-driven or
agile.
✧ In practice, most large systems are developed using a process that
incorporates elements from all of these models.

The waterfall model

Waterfall model phases
✧ There are separate identified phases in the waterfall model:
▪ Requirements analysis and definition
▪ System and software design
▪ Implementation and unit testing
▪ Integration and system testing
▪ Operation and maintenance
✧ The main drawback of the waterfall model is the difficulty of
accommodating change after the process is underway. In
principle, a phase has to be complete before moving onto the
next phase.

Waterfall model problems
✧ Inflexible partitioning of the project into distinct stages makes it
difficult to respond to changing customer requirements.
▪ Therefore, this model is only appropriate when the requirements are well-
understood and changes will be fairly limited during the design process.
▪ Few business systems have stable requirements.
✧ The waterfall model is mostly used for large systems
engineering projects where a system is developed at several
sites.
▪ In those circumstances, the plan-driven nature of the waterfall model helps
coordinate the work.

Incremental development

Incremental development benefits
✧ The cost of accommodating changing customer requirements is
reduced.
▪ The amount of analysis and documentation that has to be redone is much less than is
required with the waterfall model.
✧ It is easier to get customer feedback on the development work that
has been done.
▪ Customers can comment on demonstrations of the software and see how much has
been implemented.
✧ More rapid delivery and deployment of useful software to the
customer is possible.
▪ Customers are able to use and gain value from the software earlier than is possible with
a waterfall process.

Incremental development problems
✧ The process is not visible.
▪ Managers need regular deliverables to measure progress. If systems are
developed quickly, it is not cost-effective to produce documents that reflect
every version of the system.
✧ System structure tends to degrade as new increments are
added.
▪ Unless time and money is spent on refactoring to improve the software, regular
change tends to corrupt its structure. Incorporating further software changes
becomes increasingly difficult and costly.

Integration and configuration
✧ Based on software reuse where systems are integrated from
existing components or application systems (sometimes
called COTS -Commercial-off-the-shelf) systems).
✧ Reused elements may be configured to adapt their behaviour
and functionality to a user’s requirements
✧ Reuse is now the standard approach for building many types
of business system
▪ Reuse covered in more depth in Chapter 15.

Types of reusable software
✧ Stand-alone application systems (sometimes called COTS)
that are configured for use in a particular environment.
✧ Collections of objects that are developed as a package to be
integrated with a component framework such as .NET or
J2EE.
✧ Web services that are developed according to service
standards and which are available for remote invocation.

Reuse-oriented software engineering

Key process stages
✧ Requirements specification
✧ Software discovery and evaluation
✧ Requirements refinement
✧ Application system configuration
✧ Component adaptation and integration

Advantages and disadvantages
✧ Reduced costs and risks as less software is developed from
scratch
✧ Faster delivery and deployment of system
✧ But requirements compromises are inevitable so system may not
meet real needs of users
✧ Loss of control over evolution of reused system elements

Process activities

Process activities
✧ Real software processes are inter-leaved sequences of technical,
collaborative and managerial activities with the overall goal of
specifying, designing, implementing and testing a software system.
✧ The four basic process activities of specification, development,
validation and evolution are organized differently in different
development processes.
✧ For example, in the waterfall model, they are organized in sequence,
whereas in incremental development they are interleaved.

The requirements engineering process

Software specification
✧ The process of establishing what services are required and the
constraints on the system’s operation and development.
✧ Requirements engineering process
▪ Requirements elicitation and analysis
• What do the system stakeholders require or expect from the system?
▪ Requirements specification
• Defining the requirements in detail
▪ Requirements validation
• Checking the validity of the requirements

Software design and implementation
✧ The process of converting the system specification into an
executable system.
✧ Software design
▪ Design a software structure that realises the specification;
✧ Implementation
▪ Translate this structure into an executable program;
✧ The activities of design and implementation are closely related
and may be inter-leaved.

A general model of the design process

Design activities
✧ Architectural design, where you identify the overall structure of the
system, the principal components (subsystems or modules), their
relationships and how they are distributed.
✧ Database design, where you design the system data structures
and how these are to be represented in a database.
✧ Interface design, where you define the interfaces between system
components.
✧ Component selection and design, where you search for reusable
components. If unavailable, you design how it will operate.

System implementation
✧ The software is implemented either by developing a program or
programs or by configuring an application system.
✧ Design and implementation are interleaved activities for most
types of software system.
✧ Programming is an individual activity with no standard process.
✧ Debugging is the activity of finding program faults and correcting
these faults.

Software validation
✧ Verification and validation (V & V) is intended to show that a
system conforms to its specification and meets the
requirements of the system customer.
✧ Involves checking and review processes and system testing.
✧ System testing involves executing the system with test cases
that are derived from the specification of the real data to be
processed by the system.
✧ Testing is the most commonly used V & V activity.

Stages of testing

Testing stages
✧ Component testing
▪ Individual components are tested independently;
▪ Components may be functions or objects or coherent groupings of these
entities.
✧ System testing
▪ Testing of the system as a whole. Testing of emergent properties is
particularly important.
✧ Customer testing
▪ Testing with customer data to check that the system meets the customer’s
needs.

Testing phases in a plan-driven software process (V-
model)

Software evolution
✧ Software is inherently flexible and can change.
✧ As requirements change through changing business
circumstances, the software that supports the business must
also evolve and change.
✧ Although there has been a demarcation between development
and evolution (maintenance) this is increasingly irrelevant as
fewer and fewer systems are completely new.

System evolution

Coping with change
✧ Change is inevitable in all large software projects.
▪ Business changes lead to new and changed system requirements
▪ New technologies open up new possibilities for improving
implementations
▪ Changing platforms require application changes
✧ Change leads to rework so the costs of change include
both rework (e.g. re-analysing requirements) as well as
the costs of implementing new functionality

Coping with changing requirements
✧ System prototyping, where a version of the system or part of
the system is developed quickly to check the customer’s
requirements and the feasibility of design decisions. This
approach supports change anticipation.
✧ Incremental delivery, where system increments are delivered to
the customer for comment and experimentation. This supports
both change avoidance and change tolerance.

Software prototyping
✧ A prototype is an initial version of a system used to demonstrate
concepts and try out design options.
✧ A prototype can be used in:
▪ The requirements engineering process to help with requirements elicitation and
validation;
▪ In design processes to explore options and develop a UI design;
▪ In the testing process to run back-to-back tests.

Benefits of prototyping
✧ Improved system usability.
✧ A closer match to users’ real needs.
✧ Improved design quality.
✧ Improved maintainability.
✧ Reduced development effort.

The process of prototype development

Prototype development
✧ May be based on rapid prototyping languages or tools
✧ May involve leaving out functionality
▪ Prototype should focus on areas of the product that are not well-understood;
▪ Error checking and recovery may not be included in the prototype;
▪ Focus on functional rather than non-functional requirements such as
reliability and security

Throw-away prototypes
✧ Prototypes should be discarded after development as they are
not a good basis for a production system:
▪ It may be impossible to tune the system to meet non-functional requirements;
▪ Prototypes are normally undocumented;
▪ The prototype structure is usually degraded through rapid change;
▪ The prototype probably will not meet normal organisational quality standards.

Incremental delivery
✧ Rather than deliver the system as a single delivery, the
development and delivery is broken down into increments
with each increment delivering part of the required
functionality.
✧ User requirements are prioritised and the highest priority
requirements are included in early increments.
✧ Once the development of an increment is started, the
requirements are frozen though requirements for later
increments can continue to evolve.

Incremental development and delivery
✧ Incremental development
▪ Develop the system in increments and evaluate each increment before
proceeding to the development of the next increment;
▪ Normal approach used in agile methods;
▪ Evaluation done by user/customer proxy.
✧ Incremental delivery
▪ Deploy an increment for use by end-users;
▪ More realistic evaluation about practical use of software;
▪ Difficult to implement for replacement systems as increments have less
functionality than the system being replaced.

Incremental delivery

Incremental delivery advantages
✧ Customer value can be delivered with each increment, so
system functionality is available earlier.
✧ Early increments act as a prototype to help elicit
requirements for later increments.
✧ Lower risk of overall project failure.
✧ The highest priority system services tend to receive the most
testing.

Incremental delivery problems
✧ Most systems require a set of basic facilities that are
used by different parts of the system.
▪ As requirements are not defined in detail until an increment is to be
implemented, it can be hard to identify common facilities that are
needed by all increments.
✧ The essence of iterative processes is that the
specification is developed in conjunction with the
software.
▪ However, this conflicts with the procurement model of many
organizations, where the complete system specification is part of the
system development contract.

Summary
✧ Software processes are the activities involved in producing a
software system. Software process models are abstract
representations of these processes.
✧ General process models describe the organization of software
processes.
▪ Examples of these general models include the ‘waterfall’ model, incremental
development, and reuse-oriented development.
✧ Requirements engineering is the process of developing a
software specification.

Summary
✧ Design and implementation processes are concerned with
transforming a requirements specification into an executable
software system.
✧ Software validation is the process of checking that the system
conforms to its specification and that it meets the real needs of the
users of the system.
✧ Software evolution takes place when you change existing software
systems to meet new requirements. The software must evolve to
remain useful.
✧ Processes should include activities such as prototyping and
incremental delivery to cope with change.

What are the types of software
process models?
Sample footer text 3/1/20XX 61

Quiz1
What are the lifecycle of a software development?
A. SDLL
B. SDLC
C. SystemOps
D. SoftwareDev
Sample footer text 3/1/20XX 62

Components of Software Engineering
64
A framework for
the tasks required
to build high-
quality software.
An agreed, common
language used to
communicate all
aspects of the system,
from requirements to
final design.
Tools to make
working through the
process less difficult
for all involved
The actual software
product or system
built and put into
operation
Tools
Visual
Paradigm
Eclipse
Poseidon
Process
RUP
XP
Notation
UML
Product
eCommerc
e System
Mobile
App

SE - Lecture 2 - SW Devl Process.pptx

More Related Content

Similar to SE - Lecture 2 - SW Devl Process.pptx (20)

More from TangZhiSiang (12)

Recently uploaded (20)

SE - Lecture 2 - SW Devl Process.pptx