Software Engineering-Lecture 1

MARWARI COLLEGE, RANCHI

(AN AUTONOMOUS UNIT OF RANCHI UNIVERSITY FROM 2009)

- Prakash Kumar, Dept. of CA

-Archana Kumari, Dept. of CA
-Raju Manjhi, Dept. of CA

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Software Engineering:

Software engineering is the establishment and use of engineering principle to obtain economically software i.e. reliable and work efficient on real machine.

According to IEEE Software engineering is the application of a systematic discipline and quantifiable approach to the development, operation and maintenance of software.

   Software engineering is a layered technology

1)    Tools

2)    Method

3)    Process

4)    Quality

1. Quality:-The bedrock that supports Software engineering is quality focus.

2. Process:-The foundation of Software engineering is process layer that holds the technology layer to enable rational and timely development of computer system.

3.Method:-The method provide technology “how do’s for building software”.

4.Tools: - The total provides automated or semi automated for the process and method.

Software: -     Software is-

1. Introduction when executed provides desired   features and performance.

2. Data structure that enable program to manipulate information.

3. Document that describe the operation and use of the program.

FEATURES / CHARACTERISTIC SOFTWARE

1. Software is developed and engineered.

2. Software does not wear out.

3. Generally it is customized.

4. Software is flexible.

5. Re-usability of component

6. Maintainability.

Category of software

1. System software

2. Application software

3. Engineering & Scientific software.

4. Enabled software

5. Web application software

6. Artificial intelligence software.

Enabled Software: - Enabled software resides within a product or system and use to implement and control feature and functions for the end of user for the system of itself.

         

Need of Software Engineering

The need of software engineering arises because of higher rate of change in user requirements and environment on which the software is working.

• Large software – When the size of software becomes large engineering has to step to give it a scientific process.
• Scalability- If the software process were not based on scientific and engineering concepts, it would be easier to re-create new software than to scale an existing one.
• Cost- As hardware industry has shown its skills and huge manufacturing has lower down the price of computer and electronic hardware. But the cost of software remains high if proper process is not adapted.
• Dynamic Nature- The always growing and adapting nature of software hugely depends upon the environment in which user works.
• Quality Management- Better process of software development provides better and quality software product.

Characteristics of good software

A software product can be judged by what it offers and how well it can be used. This software must satisfy on the following grounds:

• Operational
• Transitional
• Maintenance

Well-engineered and crafted software is expected to have the following characteristics:

Operational

This tells us how well software works in operations. It can be measured on:

• Budget
• Usability
• Efficiency
• Correctness
• Functionality
• Dependability
• Security
• Safety

Transitional

This aspect is important when the software is moved from one platform to another:

• Portability
• Interoperability
• Reusability
• Adaptability

Maintenance

This aspect briefs about how well software has the capabilities to maintain itself in the ever-changing environment:

• Modularity
• Maintainability
• Flexibility
• Scalability

Thus, Software engineering is a branch of computer science, which uses well-defined engineering concepts required to produce efficient, durable, scalable, in-budget and on-time software products.

Essential Attributes of a good software

Software component

A software component is a software element that conforms to a component model and can be independently deployed and composed without modification according to a composition standard. A component model defines specific interaction and composition standards. A component model implementation is the dedicated set of executable software elements required to support the execution of components that conform to the model. A software component infrastructure is a set of interacting software components designed to ensure that a software system or subsystem constructed using those components and interfaces will satisfy clearly defined performance specifications. These definitions demonstrate the important relationship between a software component infrastructure, software components, and a component model.

Software process

A software process is a set of activities that leads to the production of a software product. These activities may involve the development of software from scratch in a standard programming language like Java or C. Increasingly, however, new software is developed by extending and modifying existing systems and by configuring and integrating off-the-shelf software or system components.

Software processes are complex and, like all intellectual and creative processes, rely on people making decisions and judgments.

Although there are many software processes, some fundamental activities are common to all software processes:

1. Software specification: The functionality of the software and constraints on its operation must be defined.

2. Software design and implementation:  The software to meet the specification must be produced.

3. Software validation:  The software must be validated to ensure that it does what the customer wants.

4. Software evolution:  The software must evolve to meet changing customer needs.

Software process models

Waterfall Model:

Description

The waterfall Model is a linear sequential flow. In which progress is seen as flowing steadily downwards (like a waterfall) through the phases of software implementation. This means that any phase in the development process begins only if the previous phase is complete. The waterfall approach does not define the process to go back to the previous phase to handle changes in requirement. The waterfall approach is the earliest approach and most widely known that was used for software development.

The usage

Projects which not focus on changing the requirements, for example, projects initiated from request for proposals (RFPs), the customer has a very clear documented requirements

Advantages and Disadvantages

Advantages	Disadvantages
§  Easy to explain to the users. §  Structures approach. §  Stages and activities are well defined. §  Helps to plan and schedule the project. §  Verification at each stage ensures early detection of errors/misunderstanding. §  Each phase has specific deliverables.	§  Assumes that the requirements of a system can be frozen. §  Very difficult to go back to any stage after it finished. §  A little flexibility and adjusting scope is difficult and expensive. §  Costly and required more time, in addition to the detailed plan.

V-Shaped Model

Description

It is an extension of the waterfall model, Instead of moving down in a linear way, the process steps are bent upwards after the implementation and coding phase, to form the typical V shape. The major difference between V-shaped model and waterfall model is the early test planning in the V-shaped model.

The usage

§  Software requirements clearly defined and known

§  Software development technologies and tools are well-known

Advantages and Disadvantages

Advantages	Disadvantages
§  Simple and easy to use §  Each phase has specific deliverables. §  Higher chance of success over the waterfall model due to the development of test plans early on during the life cycle. §  Works well for where requirements are easily understood. §  Verification and validation of the product in early stages of product development.	§  Very inflexible, like the waterfall model. §  Adjusting scope is difficult and expensive. §  The software is developed during the implementation phase, so no early prototypes of the software are produced. §  The model doesn’t provide a clear path for problems found during testing phases. §  Costly and required more time, in addition to detailed plan

Prototyping Model

Description

It refers to the activity of creating prototypes of software applications, for example, incomplete versions of the software program being developed. It is an activity that can occur in software development. It used to visualize some component of the software to limit the gap of misunderstanding the customer requirements by the development team. This also will reduce the iterations may occur in waterfall approach and hard to be implemented due to the inflexibility of the waterfall approach. So, when the final prototype is developed, the requirement is considered to be frozen.

It has some types, such as:

§  Throwaway prototyping: Prototypes that are eventually discarded rather than becoming a part of the finally delivered software

§  Evolutionary prototyping: prototypes that evolve into the final system through an iterative incorporation of user feedback.

§  Incremental prototyping: The final product is built as separate prototypes. At the end, the separate prototypes are merged in an overall design.

§  Extreme prototyping: used at web applications mainly. Basically, it breaks down web development into three phases, each one based on the preceding one. The first phase is a static prototype that consists mainly of HTML pages. In the second phase, the screens are programmed and fully functional using a simulated services layer. In the third phase, the services are implemented

The usage

§  This process can be used with any software developing life cycle model. While this shall be chosen when you are developing a system has user interactions. So, if the system does not have user interactions, such as a system does some calculations shall not have prototypes.

Advantages and Disadvantages

Advantages	Disadvantages
§  Reduced time and costs, but this can be a disadvantage if the developer loses time in developing the prototypes. §  Improved and increased user involvement.	§  Insufficient analysis· User confusion of prototype and finished system. §  Developer misunderstanding of user objectives. §  Excessive development time of the prototype. §  Expense of implementing prototyping

Spiral Model (SDM)

Description

It is combining elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. This model of development combines the features of the prototyping model and the waterfall model. The spiral model is favored for large, expensive, and complicated projects. This model uses many of the same phases as the waterfall model, in essentially the same order, separated by planning, risk assessment, and the building of prototypes and simulations.

The usage

It is used in the large applications and systems which built-in small phases or segments.

Advantages and Disadvantages

Advantages	Disadvantages
§  Estimates (i.e. budget, schedule, etc.) become more realistic as work progressed because important issues are discovered earlier. §  Early involvement of developers. §  Manages risks and develops the system into phases.	§  High cost and time to reach the final product. §  Needs special skills to evaluate the risks and assumptions. §  Highly customized limiting re-usability

Iterative and Incremental Model

Description

It is developed to overcome the weaknesses of the waterfall model. It starts with an initial planning and ends with deployment with the cyclic interactions in between. The basic idea behind this method is to develop a system through repeated cycles (iterative) and in smaller portions at a time (incremental), allowing software developers to take advantage of what was learned during the development of earlier parts or versions of the system.

It can consist of mini waterfalls or mini V-Shaped model

The usage

It is used in shrink-wrap application and large system which built-in small phases or segments. Also, can be used in a system has separated components, for example, ERP system. Which we can start with the budget module as a first iteration and then we can start with inventory module and so forth.

Advantages and Disadvantages

Advantages	Disadvantages
§  Produces business value early in the development lifecycle. §  Better use of scarce resources through proper increment definition. §  Can accommodate some change requests between increments. §  More focused on customer value than the linear approaches. §  Problems can be detected earlier.	§  Requires heavy documentation. §  Follows a defined set of processes. §  Defines increments based on function and feature dependencies. §  Requires more customer involvement than the linear approaches. §  Partitioning the functions and features might be problematic. §  Integration between iteration can be an issue if this is not considered during the development.

Agile Model

Description

It is based on iterative and incremental development, where requirements and solutions evolve through collaboration between cross-functional teams.

Scrum Agile Model

The usage

It can be used with any type of the project, but it needs more engagement from the customer and to be interactive. Also, it can be used when the customer needs to have some functional requirement ready in less than three weeks and the requirements are not clear enough.

Advantages and Disadvantages

Advantages	Disadvantages
§  Decrease the time required to avail some system features. §  Face to face communication and continuous inputs from customer representative leaves no space for guesswork. §  The end result is the high-quality software in the least possible time duration and satisfied customer.	§  Scalability. §  The ability and collaboration of the customer to express user needs. §  Documentation is done at later stages. §  Reduce the usability of components. §  Needs special skills for the team.

Software Development Life Cycle

Software Development Life Cycle, SDLC for short, is a well-defined, structured sequence of stages in software engineering to develop the intended software product.

SDLC Activities

SDLC provides a series of steps to be followed to design and develop a software product efficiently. SDLC framework includes the following steps: 

Communication

This is the first step where the user initiates the request for a desired software product. The user contacts the service provider and tries to negotiate the terms, submits the request to the service providing organization in writing.

Requirement Gathering

This step onwards the software development team works to carry on the project. The team holds discussions with various stakeholders from problem domain and tries to bring out as much information as possible on their requirements. The requirements are contemplated and segregated into user requirements, system requirements and functional requirements. The requirements are collected using a number of practices as given - Software Engineering

 studying the existing or obsolete system and software,

 conducting interviews of users and developers,

 referring to the database or

 collecting answers from the questionnaires.

Feasibility Study

After requirement gathering, the team comes up with a rough plan of software process. At this step the team analyzes if software can be designed to fulfill all requirements of the user, and if there is any possibility of software being no more useful. It is also analyzed if the project is financially, practically, and technologically feasible for the organization to take up. There are many algorithms available, which help the developers to conclude the feasibility of a software project.

System Analysis

At this step the developers decide a roadmap of their plan and try to bring up the best software model suitable for the project. System analysis includes understanding of software product limitations, learning system related problems or changes to be done in existing systems beforehand, identifying and addressing the impact of project on organization and personnel etc. The project team analyzes the scope of the project and plans the schedule and resources accordingly.

Software Design

Next step is to bring down whole knowledge of requirements and analysis on the desk and design the software product. The inputs from users and information gathered in requirement gathering phase are the inputs of this step. The output of this step comes in the form of two designs; logical design, and physical design. Engineers produce meta-data and data dictionaries, logical diagrams, data-flow diagrams, and in some cases pseudo codes.

Coding

This step is also known as programming phase. The implementation of software design starts in terms of writing program code in the suitable programming language and developing error-free executable programs efficiently.

Testing

An estimate says that 50% of whole software development process should be tested. Errors may ruin the software from critical level to its own removal. Software testing is done while coding by the developers and thorough testing is conducted by testing experts at various levels of code such as module testing, Software Engineering program testing, product testing, in-house testing, and testing the product at user’s end. Early discovery of errors and their remedy is the key to reliable software.

Integration

Software may need to be integrated with the libraries, databases, and other program(s). This stage of SDLC is involved in the integration of software with outer world entities.

Implementation

This means installing the software on user machines. At times, software needs post-installation configurations at user end. Software is tested for portability and adaptability and integration related issues are solved during implementation.

Operation and Maintenance

This phase confirms the software operation in terms of more efficiency and less errors. If required, the users are trained on, or aided with the documentation on how to operate the software and how to keep the software operational. The software is maintained timely by updating the code according to the changes taking place in user end environment or technology. This phase may face challenges from hidden bugs and real-world unidentified problems.