A process model can be defined as a strategy (also known as software engineering paradigm), comprising process, methods, and tools layers as well as the generalphases for developing the software. It provides a basisfor controlling various activities required to develop and maintain the software. Inaddition, it helps the software development team in facilitating and understandingthe activities involved in the project.

A process model for software engineering depends on the nature and application of the software project. Thus, it is essential to define process models for each software project. IEEE defines a process model as ‘a framework containing the processes, activities, and tasks involved in the development, operation, and maintenance of a software product, spanning the life of the system from the definition of its requirements to the termination of its use.’ A process model reflects the’ goals of software development such as developing a high quality product and meeting the schedule on time. In addition, it provides a flexible framework for enhancing the processes. Other advantages of the software process model are listed below.

Enables effective communication: It enhances understanding and provides a specific basis for process execution.

Facilitates process reuse: Process development is a time consuming and expensive activity. Thus, the software development team utilizes the existing processes for different projects.

Effective: Since process models can be used again and again; reusable processes provide all effective means for implementing processes for software development.

Facilitates process management: Process models provide a framework for defining process status criteria and measures for software development. Thus, effective management is essential to provide a clear description of the plans for the software project.

Every software development process model takes requirements as input and delivers products as output. However, a process should detect defects in the phases in which they occur. This requires Verification and Validation (V&V) of the products after each and every phase of the software development life cycle.

Verification is the process of evaluating a system or its components for determining the product developed at the end of each phase of the software development. IEEE defines verification as ‘a process for determining whether the software products of an activity fulfill the requirements or conditions imposed on them in the previous activities.’ Thus, verification confirms that the product is transformed from one form to another as intended and with sufficient accuracy.

Validation is the process of evaluating the product at the end of each phase to check whether the requirements are fulfilled. In addition, it is the process of establishing a procedure and method, which provides the intended outputs. IEEE defines validation as ‘a process for determining whether the requirements and the final, as-built system or software product fulfils its specific intended use.’ Thus, validation substantiates the software functions with sufficient accuracy with respect to its requirements specification.

Various kinds of process models are waterfall model, prototyping model, spiral model, incremental model, time-boxing model, RAD model, V model, build and fix model, and formal method model.

Waterfall Model

In the waterfall model (also known as the classical life cycle model), the development of software proceeds linearly and sequentially from requirement analysis to design, coding, testing, integration, implementation, and maintenance. Thus, this model is also known as the linear sequential model.

This model is simple to understand and represents processes which are easy to manage and measure. The waterfall model comprises different phases and each phase has its distinct goal. After the completion of one phase, the development of software moves to the next phase. Each phase modifies the intermediate product to develop a new product as an output. The new product becomes the input of the next process. Table lists the inputs and outputs of each phase of waterfall model.

                 Table Inputs and Outputs of each Phase of Waterfall Model

As stated earlier, the waterfall model comprises several phases, which are listed below.

System/information engineering modeling: This phase establishes the requirements for all parts of the system. Software being a part of the larger system, a subset of these requirements is allocated to it. This system view is necessary when software interacts with other parts of the system including hardware, databases, and people. System engineering includes collecting requirements at the system level while information engineering includes collecting requirements at a level where all decisions regarding business strategies are taken.

Requirements analysis: This phase focuses on the requirements of the software to be developed. It determines the processes that are to be incorporated during the development of the software. To specify the requirements, users’ specifications should be clearly understood and their requirements be analyzed. This phase involves interaction between the users and the software engineers and produces a document known as Software Requirements Specification (SRS).

Design: This phase determines the detailed process of developing the software after the requirements have been analyzed. It utilizes software requirements defined by the user and translates them into software representation. In this phase, the emphasis is on finding solutions to the problems defined in the requirements analysis phase. The software engineer is mainly concerned with the data structure, algorithmic detail and interface representations.

Coding: This phase emphasizes translation of design into a programming language using the coding style and guidelines. The programs created should be easy to read and understand. All the programs written are documented according to the specification.

Testing: This phase ensures that the software is developed as per the user’s requirements. Testing is done to check that the software is running efficiently and with minimum errors. It focuses on the internal logic and external functions of the software and ensures that all the statements have been exercised (tested). Note that testing is a multistage activity, which emphasizes verification and validation of the software.

Implementation and maintenance: This phase delivers fully functioning operational software to the user. Once the software is accepted and deployed at the user’s end, various changes occur due to changes in the external environment (these include-upgrading a new operating system or addition of a new peripheral device).The changes also occur due to changing requirements of the user and changes occurring in the field of technology. This phase focuses on modifying software, correcting errors, and improving the performance of the software.

Various advantages and disadvantages associated with the waterfall model are listed in Table.

                Table Advantages and Disadvantages of Waterfall Model

The existence of software process does not guarantee the timely delivery of the software and its ability to meet the user’s expectations. The process needs to be assessed in order to ensure that it meets a set of basic process criteria, which is essential for implementing the principles of software engineering in an efficient manner. The process is assessed to evaluate methods, tools, and practices, which are used to develop and test the software. The aim of process assessment is to identify the areas for improvement and suggest a plan for making that improvement. The main focus areas of process assessment are listed below.

1. Obtaining guidance for improving software development and test processes
2. Obtaining an independent and unbiased review of the process
3. Obtaining a baseline (defined as a set of software components and documents that have been formerly reviewed and accepted; that serves as the basis for further development) for improving quality and productivity of processes.

Software process assessment examines whether the software processes are effective and efficient in accomplishing the goals. This is determined by the capability of selected software processes. The capability of a process determines whether a process with some variations is capable of meeting user’s requirements. In addition, it measures the extent to which the software process meets the user’s requirements. Process assessment is useful to the organization as it helps in improving the existing processes. In addition, it determines the strengths, weaknesses and the risks involved in the processes.

The process assessment leads to process capability determination and process improvement. Process capability determination is an organized assessment, which analyzes the software processes in an organization. In addition, process capability determination identifies the capabilities of a process and the risks involved in it. The process improvement identifies the changes to be made in the software processes. The software capability determination motivates the organization to perform software process improvement.

Different approaches are used for assessing software process. These approaches are SPICE (ISO/IEC15504), ISO 9001:2000, standard CMMI assessment method for process improvement, CMM-based appraisal for internal process improvement, and Bootstrap,

SPICE (Software Process Improvement and Capability Determination) is a standard used for both process improvement and process capability determination. SPICE provides a framework for assessing the software process and is used by the organizations involved in planning, monitoring, developing, managing, and improving acquisitions. It is carried out in accordance with the International Organization for Standardization (ISO) and International Electro-technical Committee (IEC), which are used together and known as ISO/IEC 15504. The functions of SPICE (ISO/IEC 15504) are listed below.

1. To develop process-rating profiles instead of pass or fail criteria
2. To consider the environment in which the assessed process operates
3. To facilitate self assessment
4. To ensure suitability for all applications and all sizes of organizations.

SPICE (ISO/IEC 15504) constitutes a set of documents that is used to guide goals and fundamental activities and grade the organization according to its level of capability. In addition, it determines the capability of a process in an organization, based on the results of the assessment of the processes and products. It also develops a maturity model for process improvement. This model is known as SPICE reference model. It is applicable for all processes and comprises following six levels.

1. Not performed: At this level, the processes are unable to accomplish the required outcomes. Thus, no identifiable products are created.
2. Performed informally: At this level, the implemented process accomplishes the defined outcomes. It is not planned and tracked; rather it depends on individual knowledge and identifiable products.
3. Planned and tracked: At this level, the defined process delivers products according to quality requirements within a specified time. The processes and products are verified according to the procedures, standards, and requirements.
4. Well-defined: At this level, the processes based on software engineering principles which are capable of achieving defined outcomes are used.
5. Quantitatively controlled: At this level, the performance measures, prediction capability and objective management are evaluated quantitatively. In addition, existing processes perform consistently within the defined limits to accomplish the desired outputs.
6. Continuously improved: At this level, the existing processes adapt to meet future business goals. For continuous improvement, various kinds of statistical methods are used.

ISO (International Organization for Standardization) established a standard known as ISO 9001:2000 to determine the requirements of quality management systems. A quality management system refers to the activities within an organization, which satisfies the quality related expectations of customers. Organizations ensure that they have a quality management system by demonstrating their conformance to the ISO 9001:2000 standard. The major advantage of this standard is that it achieves a better understanding and consistency of all quality practices throughout the organization. In addition, it strengthens the customer’s confidence in the product. This standard follows a plan-do-check-act (PDCA) cycle, which includes a set of activities that are listed below.

1. Plan: Determines the processes and resources which are required to develop a quality product according to the user’s satisfaction.
2. Do: Performs activities according to the plan to create the desired product.
3. Check: Measures whether the activities for establishing quality management according to the requirements are accomplished. In addition, it monitors the processes and takes corrective actions to improve them.
4. Act: Initiates activities which constantly improve processes in the organization.

An appraisal examines processes to determine their strengths and weaknesses in an organization. The appraisal used in an organization evaluates the internal processes (series of procedures occurring in the organization) for establishing or updating process improvement. In addition, appraisal includes measuring the process improvement progress by conducting audits of the processes. To conduct an appraisal, a scheme known as SCAMPI was developed by the Software Engineering Institute (SEI).

SCAMPI is used for process improvement by gaining insight into the process capability in the organization. The major advantage of SCAMPI is that it supports process improvement and establishes a consensus within the organization regarding areas where the process improvements are needed. The major characteristics of SCAMPI are listed in Table.

                                                Table SCAMPI Characteristics

SCAMPI enables an organization to select and follow an approach for developing a plan for appraisal, which is appropriate for the requirements. These appraisal requirements in CMMI (ARC) comprise criteria for developing, defining, and utilizing the appraisal methods (namely, Class A, Class B, and Class q, which are based on Capability Maturity Model Integration (CMMI) as an improved framework. The objectives of SCAMPI are listed below.

1. To identify strengths and weaknesses of existing processes in the organization
2. To specify an integrated appraisal method for internal process improvement
3. To act as a motivation for initiating and focusing on software process improvement.

SCAMPI is an appropriate tool for benchmarking within the organization. This process emphasizes a rigorous method that is capable of achieving high accuracy and reliability of appraisal results. The major characteristics of classes ‘A’, ‘B’, and ‘C’ are listed in Table. Class ‘A’ assessment method should satisfy all appraisal requirements of CMMI. The major characteristic of Class ‘A’ assessment is a detailed assessment of process (es).With a thorough coverage, the strengths and weaknesses of processes are determined. SCAMPI is a Class ‘A’ assessment method for process improvement.

Class ‘B’ appraisal method should comply with a subset of ARC requirements. As shown in Table, requirements of the Class ‘A’ method are optional for, Class ‘B’. Class ‘B’ assessment helps the organization to gain insight into its process capability. It focuses on areas that need improvement. It does not emphasize detailed coverage and is not efficient for level rating. These types of appraisals are considered efficient for initial assessment in organizations that have just started to use CMMI for process improvement activities. In addition, it is useful in providing a cost effective measure for performing interim assessment and capability evaluations.

                                        Table Characteristics of Appraisal Methods

Class ‘C’ appraisal methods are inexpensive and used for a short duration. In addition, they provide quick feedback to the result of the assessment. In other words, these appraisal methods are useful for periodic assessment of the projects.

Class ‘B’ and Class ‘C’ appraisals are useful for organizations that do not require generation of ratings. The primary reason for all appraisal methods should be to identify the strengths and weaknesses of the processes for their improvements.

CBA-IPI tool is used in an organization to gain insight into the software development capability. For this, the strengths and weaknesses of the existing process are identified in order to prioritize software improvement plans and focus on software improvements, which are beneficial to the organization. The organization’s software process capability is assessed by a group of individuals known as the assessment team, which generates findings and provides ratings according to the CMM (Capability Maturity Model). These findings are collected from questionnaires, document reviews and interviews with the managers of the organization. Thus, the primary goal of CBA IPI is to provide an actual picture of the existing processes in an organization. To achieve this, the assessment team performs the following functions.

1. Provides data as a baseline to the organization in order to check its software capability
2. Identifies issues that have an impact on the process improvement
3. Provides sufficiently complete findings to the organization. These are used to guide the organization in planning .and prioritizing future process improvement activities.

For an assessment to be considered in CBAIPI, it should satisfy the minimum requirements concerning the assessment team, assessment plan, data collection, data validation, and reporting of the assessment results. These requirements are listed in Table.

                                               Table Requirements in CBA IPI

The CBA IPI method is similar to SCAMPI as both are used for process assessment in an organization. However, differences do exist between the two approaches. These differences are listed in Table.

                              Table Differences between CBA IPI and SCAMPI

Bootstrap is an improvement on SEI approaches for process assessment and improvement and covers the requirements laid by ISO 9000. This approach evaluates and improves the quality of software development and management process of an organization. It defines a framework for assessing and promoting process improvement. The basic objectives of this approach are listed below.

1. To support evaluation of the process capability
2. To identify the strengths and weaknesses of the processes in the organization being assessed
3. To support the accomplishment of goals in an organization by planning improved actions
4. To increase the effectiveness of the processes while implementing Standard requirements in the organization.

The main feature of the bootstrap approach is the assessment process, which leads to an improvement in the software development processes. During the assessment, the organizational processes are evaluated to define each process. Note that after the assessment is done, data is collected in a central database. In addition, it provides two questionnaires (forms containing a set of questions, which are distributed to people to gain statistical information): the first to gather data about the organization that develops the software and the second to gather data about the projects.

To accomplish a set of tasks, it is important to go through a sequence of predictable steps. This sequence of steps refers to a road map, which helps in developing a timely, high quality, and highly efficient product or system. Road map, commonly referred to as software process, comprises activities, constraints, and resources that are used to produce an intended system. Software process helps to maintain a level of consistency and quality in products or services that are produced by different people.

The software development process, also known as the software life cycle, describes the evolution of the software product from its conception through itsdesign, implementation, delivery, and finally to its maintenance. This chapterdiscusses software process, standards used to assess software process, variousprocess models, and the organizational process.

SOFTWARE PROCESS, PROJECT, AND PRODUCT

Software engineering comprises interrelated and recurring entities, which are essential for software development. Software is developed efficiently and effectively with the help of well defined activities or processes. In general, a process is defined as a series of steps involving activities and resources, which produces the desired output. Software process is defined as a collection of procedures to develop the software product according to certain goals or standards. Generally, the following points are noted about software process.

1. It uses resources subject to given constraints and produce intermediate and final products.
2. It is composed of sub processes that are organized in such a manner that each sub process has its own process model.
3. It is carried out with an entry and exit criteria that helps in monitoring the beginning and completion of the activity.
4. It includes guidelines, which explain the objectives of each activity.
5. It is vital because it imposes uniformity on the set of activities.
6. It is regarded as more than just a procedure, tools or techniques, which are collectively used in a structured manner to produce a product.
7. It includes various technical and managerial issues, which are required to develop the software.

                         The characteristics of software processes are listed in Table.

A project is defined as a specification essential for developing or maintaining a specific product. Software project is developed when software processes are executed for certain specific requirements of the user. Thus, by using software process, the software project can be easily developed. The activities in software project comprise various tasks for managing resources and developing products. The software project involves people (developers, project manager, end-users, and so on) also referred to as participants who use software processes to create a product according to the user’s requirements. The participants play a major role in the development of the project and select the appropriate process for the project. In addition, a project is efficient if it is developed within the time constraint. The outcome or the result of the software project is known as a product. Thus, a software project uses software processes to create a product.

Software process can be used in the development of many software projects, each of which can produce one or more software products. Software project begins with requirements and ends with the accomplishment of the requirements. Thus, the software process should be performed to develop the final software by accomplishing user’s requirements.

Software Process Components

The objective of the software process is to develop a product, which accomplishes user’s requirements. The major components of the software process include a process management process and a product engineering process. The Process Management Process (PMP) aims at improving software processes so that a cost effective and high-quality product is developed. For this, the existing processes of the completed projects are examined. The process of comprehending the existing process, analyzing its properties, determining how to improve it, and then effecting the improvement is carried out by PMP.A group known as the Software Engineering Process Group (SEPG) performs the activities of the process management.

Based on above mentioned analysis, the product engineering processes are improved, thereby improving the software process. The aim of the product engineering process is to develop the product according to the user’s requirements. The product engineering process comprises three major components, which are listed below.

Development process: It is the process which is used during the development of the software. It specifies the development and quality assurance activities that are to be performed. Programmers, designers, testing personnel, etc., perform these processes.

Project management process: It is concerned with the set of activities or tasks, which are used to successfully accomplish a set of goals. It provides the means to plan, organize, and control the allocated resources to accomplish project costs, time, and performance objectives. For this, various processes, techniques, and tools are used to achieve the objectives of the project. Project management team performs the activities of this process.

Configuration control process: It manages changes that occur as a result of modifying the requirements. In addition, it maintains integrity of the products with the changed requirements. The activities in configuration control processes are performed by a group called the Configuration Control Board (CCB).

Note that the project management process and configuration control process depend on the development process. The management process aims to control the development process, depending on the activities in the development process.

Process Framework

Process framework determines the processes which are essential for completing a complex software project. This framework identifies certain activities, known as framework activities, which are applicable to all software projects regardless of their type and complexity. Some of the framework activities are listed below.

1. Communication: It involves communication with the user so that the requirements are easily understood.
2. Planning: It establishes a plan for accomplishing the project. It describes the schedule for the project, the technical tasks involved, expected risks, and the required resources.
3. Modeling: It encompasses creation of models, which allow the developer and the user to understand software requirements and the designs to achieve those requirements.
4. Construction: It combines generation of code with testing to uncover errors in the code.
5. Deployment: It implies that the final product (software) is delivered to the user. The user evaluates the delivered product and provides feedback based on the evaluation.

In addition to framework activities, process framework also comprises a set of activities known as umbrella activities, which are used throughout the software process. These activities are listed below.

1. Software project tracking and control: It monitors the actual process so that management can take necessary steps if the software project deviates from the plans laid down. It involves tracking procedures and reviews to check whether the software project is according to user’s requirements. A documented plan is used as a basis for tracking the software activities and revising the plans.
2. Formal technical reviews: It assesses the code, products and documents of software engineering practices to detect and remove errors.
3. Software quality assurance: It assures that the software is according to the requirements. In addition, it is designed to evaluate the processes of developing and maintaining quality of the software.
4. Reusability management: It determines the criteria for products reuse and establishes mechanisms to achieve reusable Components.
5. Software configuration management: It manages the changes made in the software processes of the products throughout the life cycle of the software project. It controls changes made to the configuration and maintains the integrity in the software development process.
6. Risk management: It identifies, analyzes, evaluates and eliminates the possibility of unfavourable deviations from expected results, by following a systematic activity and then develops strategies to manage them.

Software engineering employs a well defined and systematic approach to develop software. This approach is considered to be the most effective way of producing high-quality software. However, despite this systematic approach in software development, there are still some serious challenges faced by software engineering. Some of these challenges are listed below.

1. The methods used to develop small or medium-scale projects are not suitable when it comes to the development of large-scale or complex systems.
2. Changes in software development are unavoidable. In today’s world, changes occur rapidly and accommodating these changes to develop complete software is one of the major challenges faced by the software engineers.
3. The advancement in computer and software technology has necessitated for the changes in nature of software systems. The software systems that cannot accommodate changes are not of much use. Thus, one of the challenges of software engineering is to produce high quality software adapting to the changing needs within acceptable schedules. To meet this challenge, the object oriented approach is preferred, but accommodating changes to software and its maintenance within acceptable cost is still a challenge.
4. Informal communications take up a considerable portion of the time spent on software projects. Such wastage of time delays the completion of projects in the specified time.
5. The user generally has only a vague idea about the scope and requirements of the software system. This usually results in the development of software, which does not meet the user’s requirements.
6. Changes are usually incorporated in documents without following any standard procedure. Thus, verification of all such changes often becomes difficult.
7. The development ofl1igh-quality and reliable software requires the software to be thoroughly tested. Though thorough testing of software consumes the majority of resources, underestimating it because of any reasons deteriorates the software quality.

In addition to the above mentioned key challenges, the responsibilities of the system analyst, designers, and programmers are usually not well defined. Also, if the user requirements are not precisely defined, software developers can misinterpret the meaning. All these challenges need to be addressed in order to ensure that the software is developed within the specified time and estimated costs and also meets the requirements specified by the user.

Software engineering discipline is the result of advancement in the field of technology. In this section, we will discuss various innovations and technologies that led to the emergence of software engineering discipline.

Early Computer Programming

As we know that in the early 1950s, computers were slow and expensive. Though the programs at that time were very small in size, these computers took considerable time to process them. They relied on assembly language which was specific to computer architecture. Thus, developing a program required lot of effort. Every programmer used his own style to develop the programs.

High Level Language Programming

With the introduction of semiconductor technology, the computers became smaller, faster, cheaper, and reliable than their predecessors. One of the major developments includes the progress from assembly language to high-level languages. Early high level programming languages such as COBOL and FORTRAN came into existence. As a result, the programming became easier and thus, increased the productivity of the programmers. However, still the programs were limited in size and the programmers developed programs using their own style and experience.

Control Flow Based Design

With the advent of powerful machines and high level languages, the usage of computers grew rapidly: In addition, the nature of programs also changed from simple to complex. The increased size and the complexity could not be managed by individual style. It was analyzed that clarity of control flow (the sequence in which the program’s instructions are executed) is of great importance. To help the programmer to design programs having good control flow structure, flowcharting technique was developed. In flowcharting technique, the algorithm is represented using flowcharts. A flowchart is a graphical representation that depicts the sequence of operations to be carried out to solve a given problem.

Note that having more GOTO constructs in the flowchart makes the control flow messy, which makes it difficult to understand and debug. In order to provide clarity of control flow, the use of GOTO constructs in flowcharts should be avoided and structured constructs-decision, sequence, and loop-should be used to develop structured flowcharts. The decision structures are used for conditional execution of statements (for example, if statement). The sequence structures are used for the sequentially executed statements. The loop structures are used for performing some repetitive tasks in the program. The use of structured constructs formed the basis of the structured programming methodology.

Structured programming became a powerful tool that allowed programmers to write moderately complex programs easily. It forces a logical structure in the program to be written in an efficient and understandable manner. The purpose of structured programming is to make the software code easy to modify when required. Some languages such as Ada, Pascal, and dBase are designed with features that implement the logical program structure in the software code.

Data-Flow Oriented Design

With the introduction of very Large Scale Integrated circuits (VLSI), the computers became more powerful and faster. As a result, various significant developments like networking and GUIs came into being. Clearly, the complexity of software could not be dealt using control flow based design. Thus, a new technique, namely, data-flow-oriented technique came into existence. In this technique, the flow of data through business functions or processes is represented using Data-flow Diagram (DFD). IEEE defines a data-flow diagram (also known as bubble chart and work-flow diagram) as ‘a diagram that depicts data sources, data sinks, data storage, and processes performed on data as nodes, and logical flow of data as links between the nodes.’

Object Oriented Design

Object-oriented design technique has revolutionized the process of software development. It not only includes the best features of structured programming but also some new and powerful features such as encapsulation, abstraction, inheritance, and polymorphism. These new features have tremendously helped in the development of well-designed and high-quality software. Object-oriented techniques are widely used these days as they allow reusability of the code. They lead to faster software development and high-quality programs. Moreover, they are easier to adapt and scale, that is, large systems can be created by assembling reusable subsystems.

Software engineering shares common interest with other engineering disciplines. Like other engineering domains where a given problem (for example, building a bridge) can be solved by following a series of interrelated steps, the software development process also comprises a number of steps or phases. The main objective of software engineering is to develop methods for large systems, which help developers obtaining high-quality software in minimum time and at low cost. Therefore, it is essential to perform software development in phases. This phased development of software is often referred to as the software development life cycle (SDLC) or software life cycle.

A software development process comprises different phases. These phases follow a top-to-bottom approach, implying that the phases take inputs from the previous phases, add features, and then produce outputs. The outputs from different phases are referred to as intermediate product, work product, or derivable. Various phases involved in the systematic development of software. The phases of the software development process are shown as a comparison to the process of building a bridge in Table.

                               Table   Building Bridge and Corresponding SDLC Phase

This phase commences with discussion on the requests made by the user. The requests can be for a new system or for modifying the existing one. In this phase, it is determined whether the user’s requirements can be met with the available hardware and software technologies. Preliminary investigation verifies the problem and understands the need for the required system. It involves determining whether the proposed system is beneficial for business and can be developed within the specified budget. In addition, the time factor that determines the duration of the project is also considered.

Preliminary investigation should be quick and cost effective. The output of preliminary investigation decides whether the new system should be developed. There are three constraints on which the decision to go ahead or not depends. These are listed below.

1. Technical: This evaluation determines whether technology needed for the proposed system is available and if it is available, then how it can be integrated within the organization. Technical evaluation also determines whether the existing system can be upgraded to use new technology and’ whether the organization has the expertise to use it.
2. Time: This evaluation determines the time needed to complete a project. Time factor is an important issue in software development as cost increases with an increase in the time period of a project.
3. Budgetary: This evaluation looks at the financial aspect of the project. Budgetary evaluation determines whether the investment needed to implement the system will be recovered at later stages.

This phase studies the problems or requirements of software in detail. These requirements define the processes to be managed during the software development. After analyzing the requirements of the user, a requirements statement known as Software Requirements Specification (SRS) is developed. After analysis, planning for the project begins, which includes developing plans that describe the activities to be performed during the project development such as software configuration management plans, project and scheduling, and quality assurance plans. In addition, the resources required during the project are also determined.

In this phase, the requirements are given a ‘defined’ form. Design can be defined as a process of deciding information structures in terms of efficiency, flexibility, and reusability. Software design serves as the blueprint for the implementation of requirements in the software system. Each element of the analysis model in the analysis phase provides information that can be used for creating design models. The requirements specification of software together with data, functional, and behavioural model provides a platform to feed the design task to achieve the desired functionality and quality.

First, a top level design is made to outline the problem solution. Next, detailed designing is carried out to specify all the details needed so that the programmers can easily implement the1design. Some of the basic design principles that are used for a good design practice are listed below.

1. Software design should be traceable to the analysis model: As a single design element often traces multiple requirements, it becomes essential to have a means for tracking how requirements are satisfied by a design model.
2. Software design should demonstrate uniformity and integration: A design is said to be uniform if its appearance is consistent in the design model. In most cases, rules, formats, and styles are defined in advance to the design team before the design work begins.
3. Software design should be structured to adapt to changes: The software design should be flexible enough to adapt to changes easily. To achieve the flexibility, the basic design concepts such as abstraction, refinement, and modularity should be applied effectively.
4. Software design should endeavour to minimize conceptual (Semantic) Errors: The design team ensures that major conceptual elements of designsuch as ambiguity and inconsistency have been addressed in advance.

The coding phase can be defined as a process of translating the software requirements into a programming language, using tools that are available. Writing an efficient software code requires a thorough knowledge of programming language and its tools. Therefore, it is important to choose the appropriate programming language according to the user’s requirements. A program code is efficient if it makes optimal use of resources and contains minimum errors.

To write software code efficiently and with minimum errors in a programming language, a coding style is followed. A coding style comprises several guidelines known as coding guidelines that are used to implement individual programming language constructs, comments, formatting, and so on. The objective of using these guidelines is to reduce complexity and errors in programs and improve the understanding of the source code. A set of comprehensive coding guidelines encompasses all aspects of code development. To ensure that all developers work in a harmonized manner (the source code should reflect a harmonized style as if a single developer has written the entire code in one session), the developers should be aware of the coding guidelines before the inception of a software project.

Software testing is performed to ensure that the software is free from errors. Efficient testing improves the quality of software. To achieve high-quality software, testing requires a thorough analysis of the software in a systematic manner. A test plan is created to test software in a planned and systematic manner. In addition, software testing is performed to ensure that the software produces the correct output. This implies that outputs produced should be according to user requirements, produced by following rules and guidelines. These rules and guidelines that are followed while performing testing are known as principles of software testing and help perform testing efficiently and effectively. The commonly followed principles for software testing are listed below.

• Define the expected output: When programs are executed during software testing, they mayor may not produce the expected output. This can be due to different errors present in the software. Hence, before software testing begins, it is necessary to define the expected output.
• Inspect output of each test completely: The output of each test should be inspected thoroughly in order to determine the performance and functionality of the software.
• Include test cases for invalid and unexpected conditions: Software produces correct outputs when it is tested using precise or expected inputs. However, if an unexpected input is given to software, it may produce erroneous outputs. Hence, it is necessary to develop test cases that detect errors, when unexpected and incorrect inputs are given.
• Test the modified program to check its expected performance: Sometimes, when certain modifications (such-as adding new functions) are made in the software, it may produce unexpected outputs. Hence it is necessary to test the software after modifications to check whether it performs in the expected manner.
• Plan test to find errors: Testing is planned with an intention of finding errors in software. It should be viewed as a process that locates errors rather than as one that proves the correctness of the software.

This phase comprises a set of software engineering activities that occur after the software has been delivered to the user. The objective of this phase is to make the software operational as per the user requirements and to provide continuity of service. To achieve this objective, software maintenance focuses on fixing errors, recovering from failures such as hardware failures or incompatibility of hardware with software. In addition, it facilitates future maintenance work by modifying the software code and databases used in the software.

After the software is developed and delivered, it may require changes. Sometimes, changes are made in a software system when user requirements are not completely met. To make changes in a software system, the software maintenance process evaluates, controls, and implements changes. Note that changes can also be forced on the software system because of changes in government regulations or in policies of the organization.

Software is developed using different software process models. It must be noted that software maintenance is applicable to every software system regardless of the software process model followed. Software maintenance is performed to accomplish tasks such as detecting and fixing errors, supporting enhancements, and improving software to accomplish user requirements.

Over the last 50 years there has been revolutionary advancement in the field of technology, leading to improvements in hardware performance and profound changes in computing architectures. This advancement has led to the production of complex computer-based systems that are capable of providing information in a wide variety of formats. The increase in computer power has made unrealistic computer applications a feasible proposition, marking the genesis of an era where software products are far more complex as compared to their predecessors. By using software engineering practices, these complex systems can be developed in a systematic and efficient manner. [Read more…] about Definition of Software Engineering and Software Engineering Layers

In the late 1960s, it became clear that the development of software is different from manufacturing other products. This is because employing more manpower (programmers) later in the software development does not always help speed up the development process. Instead, sometimes it may have negative impacts like delay in achieving the scheduled targets, degradation of software quality, etc. Though software has been an important element of many systems since a long time, developing software within a certain schedule and maintaining its quality is still difficult.

History has seen that delivering software after the scheduled date or with errors has caused large scale financial losses as well as inconvenience to many. Disasters such as the Y2Kproblem affected economic, political, and administrative systems of various countries around the world. This situation, where catastrophic failures have occurred, is known as software crisis. The major causes of software crisis are the problems associated with poor quality software such as malfunctioning of software systems, inefficient development of software, and the most important, dissatisfaction amongst the users of the software.

The software market today has a turnover of more than millions of rupees. Out of this, approximately thirty Percent of software is used for personal computers and the remaining software is developed for specific users or organizations. Application areas such as the banking sector are completely dependant on software application. Software failures in these technology-oriented areas have led to considerable loss in terms of time, money, and even human lives. History has been witness to many such failures, some of which are listed below.

1. The Northeast blackout in 2003 has been one of the major power system failures in the history of North America. This blackout involved failure of 100 power plants due to which almost 50 million customers faced power loss that resulted in financia110ss of approximately $6 billion. Later, it was determined that the major reason behind the failure was a software bug in the power monitoring and management system.
2. Year 2000 (Y2K) problem refers to the widespread snags in processing dates after the year 2000. The roots ofY2K problem can be traced back to 1960-80 when developers shortened the 4-digit date format like 1972 to a 2-digit format like 72 because of limited memory. At that time they did not realize that year 2000 will be shortened to 00 which is less than 72. In the 1990s, experts began to realize this major shortcoming in the computer application and then millions were spent to handle this problem.
3. In 1996, Arian-5 space rocket, developed at the cost of $7000 million over a period of 10 years was destroyed within less than a minute after its launch. The crash occurred because there was a software bug in the rocket guidance system.
4. In 1996, one of the largest banks of US credited accounts of nearly 800 customers with approximately $9241acs. Later, it was detected that the problem occurred due to a programming bug in the banking software.
5. During the Gulf War in 1991, the United States of America used Patriot missiles as a defense against Iraqi Scud missiles. However, the Patriot failed to hit the Scud many times. As a result, 28 US soldiers were killed in Dhahran, Saudi Arabia. An inquiry into the incident concluded that a small bug had resulted in the miscalculation of missile path.

The development of software requires dedication and understanding on the developers’ part. Many software problems arise due to myths that are formed during the initial stages of software development. Unlike ancient folklore that often provides valuable lessons, software myths propagate false beliefs and confusion in the minds of management, users and developers.

Managers, who own software development responsibility, are often under strain and pressure to maintain a software budget, time constraints, improved quality, and many other considerations. Common management myths are listed in Table.

                                                 Table Management Myths

In most cases, users tend to believe myths about the software because software managers and developers do not try to correct the false beliefs. These myths lead to false expectations and ultimately develop dissatisfaction among the users. Common user myths are listed in Table.

                                                    Table User Myths

In the early days of software development, programming was viewed as an art, but now software development has gradually become an engineering discipline. However, developers still believe in some myths-. Some of the common developer myths are listed in Table.

                                                 Table Developer Myths

In earlier times, software was simple in nature and hence, software development was a simple activity. However, as technology improved, software became more complex and software projects grew larger. Software development now necessitated the presence of a team, which could prepare detailed plans and designs, carry out testing, develop intuitive user interfaces, and integrate all these activities into a system. This new approach led to the emergence of a discipline known as software engineering. [Read more…] about What is software? Characteristics and Classification of Software.