SDLC – A Brief Introduction IVS-TRAINING

Ground Rules Please mute your mobile phones Stick to timeliness Help each other in learning – as learning is a continuous process Please participate actively to make the session interactive:

Session Objectives Life Cycle of Software Development. Models of SDLC Concepts of various models of SDLC

At the End of Session you would be able to: What is SDLC? Various SDLC Models. Difference between SDLC and Exploratory models.

Contents Product, Process and Methods Methodologies followed in late 60’s for software Development What is SDLC? SDLC Models Classifications of SDLC Model Sequential Model Progressive Model Iterative Model Spiral model Other Models Differences between Exploratory & SDLC Models

Product, Process and Methods Product includes some of: hardware , software , documentation , installation, etc. Process Process defines a framework for a set of key process areas that must be established for effective delivery of software engineering technology. involves all of: communication (internal and external) , standards (definition and adherence) , planning and monitoring , tools and methodologies , quality assurance Role of Processes Increasingly, software suppliers recognize that software development process capability is a key source of competitive advantage. Competition forces suppliers to improve processes to meet the conflicting demands of higher quality, lower cost, and compressed schedules. Method Methods provides the technical “how to’s” for building software

Methodologies followed in late 60’s for software Development

Methodologies followed in late 60’s for software Development The Software was developed on a Trial & Error basis. No Specific Process was followed during the development of the Product. Defects were detected only after the product is delivered to the external Users. This resulted in software crisis Software fail to meet user requirements. Softwares used to crash frequently. Development of Software became expensive. Software became difficult to alter, debug, and enhance. The Software was often delivered late. Software use resources non-optimally.

Some Root Causes for Failure Inaccurate understanding of end-user-needs Ad hoc requirements management Ambiguous and imprecise communication Overwhelming complexity Undetected inconsistencies in requirements, design and implementations Insufficient testing resulting in late discovery of serious flaws Poor software quality Failure to attack risk Insufficient use of automation tools

Software Development Life Cycle (SDLC)

What is SDLC ? The various activities which are undertaken when developing software are commonly modeled as a software development lifecycle. The software development lifecycle begins with the identification of a requirement for software and ends with the formal verification of the developed software against that requirement. The software development lifecycle does not exist by itself, it is in fact part of an overall product lifecycle. Within the product lifecycle, software will undergo maintenance to correct errors and to comply with changes to requirements. The simplest overall form is where the product is just software, but it can become much more complicated, with multiple software developments each forming part of an overall system to comprise a product.

SDLC - Models SDLC - Models

SDLC Models There are a number of different models for software development lifecycles which explains the series of steps through which the product progresses. Life cycle models describe the interrelationships between software development phases. It specifies the relationships between project phases, including transition criteria, feedback mechanisms, milestones, baselines, reviews, and deliverables. Typically, a life cycle model addresses the following phases of a software project: requirements phase, design phase, implementation, integration, testing, operations and maintenance.

Importance of Lifecycle Models Provide guidance for project management what major tasks should be tackled next? milestones! what kind of progress has been made? The necessity of lifecycle models character of software development has changed early days: programmers were the primary users modest designs; potential of software unknown more complex systems attempted more features, more sophistication  greater complexity, more chances for error heterogeneous users

Classifications of SDLC Model Spiral Incremental

1. Sequential Model The models used for the software development lifecycle have been sequential, with the development progressing through a number of well defined phases. The sequential phases are usually represented V Model Waterfall Model.

Different Phases of Sequential Model : Requirements phase - in which the requirements for the software are gathered and analyzed, to produce a complete and unambiguous specification of what the software is required to do Detailed Design phase - where the detailed implementation of each component is specified. Code and Unit Test phase - in which each component of the software is coded and tested to verify that it faithfully implements the detailed design. Software Integration phase - in which progressively larger groups of tested software components are integrated and tested until the software works as a whole. System Integration phase - in which the software is integrated to the overall product and tested. Acceptance Testing phase, where tests are applied and witnessed to validate that the software faithfully implements the specified requirements. Note: Software specifications will be products of the first three phases of this lifecycle model. The remaining four phases all involve testing the software at various levels, requiring test specifications against which the testing will be conducted as an input to each of these phases.

a. V Model Requirement Specifications User Acceptance Testing High Level Design System Testing Detail Design Integration Testing Program Specification Unit Testing Coding

b. Waterfall Model Requirements Specification Architectural Design Detailed Design Code and Unit Testing Software Integration System Integration Acceptance Testing

Advantages of Waterfall Model Enforced discipline through documents no phase is complete until the docs are done & checked by SQA group concrete evidence of progress Testing is inherent in every phase continuously as well as at end of phases Verification of the Software is easy.

Drawbacks of Waterfall Model Document-driven model customers cannot understand these imagine an architect just showing you a textual spec! first time client sees a working product is after it has been coded. Problem here? leads to products that don’t meet customers needs Assumes feasibility before implementation re-design is problematic works best when you know what you’re doing when requirements are stable & problem is well-known

2. Progressive Model A common problem with software development is that software is needed quickly, but it will take a long time to fully develop. The solution is to form a compromise between timescales and functionality, providing "interim" deliveries of software, with reduced functionality, but serving as a stepping stones towards the fully functional software. It is also possible to use such a stepping stone approach as a means of reducing risk. The usual names given to this approach to software development are progressive development or phased implementation. Within a progressive development lifecycle, each individual phase of development will follow its own software development lifecycle, typically using a V or waterfall model.

2. Progressive Model - Structure Phase 1 Development Interim Delivery 1 Phase 2 Development Interim Delivery 2 Final Phase Final Delivery 2

3. Iterative Model Requirements Design Review Implementation and Test An iterative lifecycle model does not attempt to start with a full specification of requirements. Instead, development begins by specifying and implementing just part of the software, which can then be reviewed in order to identify further requirements. This process is then repeated, producing a new version of the software for each cycle of the model.

3. Iterative Model - Phases Requirements phase, in which the requirements for the software are gathered and analyzed. Iteration should eventually result in a requirements phase which produces a complete and final specification of requirements. Design phase, in which a software solution to meet the requirements is designed. This may be a new design, or an extension of an earlier design. Implementation and Test phase, when the software is coded, integrated and tested. Review phase - in which the software is evaluated, the current requirements are reviewed, and changes and additions to requirements proposed

3. Spiral model The Spiral Model - an iterative (evolutionary) system development life cycle developed by Boehm (1988) which incorporates risk assessment. Developed in recognition of the fact that systems development projects tend to repeat the stages of analysis, design and code as part of the prototyping process. Model closely related to RAD, as it implies iterative development with a review possible after each iteration or spiral - which corresponds to the production of one prototype or incremental version. Spiral model includes best features of both the classic Waterfall SDLC and the Prototyping approach.

Spiral model ………contd Each spiral consists of four main activities: Planning: setting project objectives; defining alternatives; further planning on the next spiral; etc. Risk Analysis: analysis of alternatives & the identification & solution of risks. Development: designing, coding and testing etc. in increments. Evaluation: user evaluation of each spiral and then the final product.

Other SDLC Models Used Build and fix Model Incremental Model Prototyping Model Rapid Application Development Model

Lifecycle Models Build-and-fix develop system without specs or design modify until customer is satisfied Why doesn’t build-and-fix scale? changes during maintenance most expensive!

Incremental Model Divide project into builds each adds new functions Verify Requirements phase Specification Architectural design Operations mode Retirement Perform detailed design, imple- mentation, and integration. Test. Deliver to client. For each build: Divide project into builds each adds new functions each build integrated w/ structure & product tested as a whole Advantages ? operation product in weeks less traumatic to organization smaller capital outlay Disadvantages ? need an open architecture a big advantage come maintenance! too few builds  build-and-fix too many builds  overhead Development Maintenance

Modern Software Development Differences Between the Exploratory Style and Modern Software Development Practices Modern Software Development Use of Life Cycle Models resulting in software development through several well-defined stages Emphasis on detection of errors as close to their point of introduction as possible. Errors detected in each phase of development The entire development cycle is divided into distinct phases Periodic reviews during each phase of development cycle Software testing has become systematic Better visibility of design and code resulting in production of good quality and consistent and standard documents Thorough planning in terms of estimation scheduling monitoring mechanisms Exploratory Style Software developed on Trail and Error basis Emphasis on Error correction Errors detected only during testing Emphasis only on coding during the entire development cycle Review at the end of the development phase No specific testing process Less attention was being given to producing good quality and consistent documents Inefficient planning

Questions?

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