Systems development life cycle

A systems development life cycle is composed of a number of clearly defined and distinct work phases which are used by systems engineers and systems developers to plan for, design, build, test, and deliver information systems. Like anything that is manufactured on an assembly line, an SDLC aims to produce high-quality systems that meet or exceed customer expectations, based on customer requirements, by delivering systems which move through each clearly defined phase, within scheduled time frames and cost estimates.[3] Computer systems are complex and often (especially with the recent rise of service-oriented architecture) link multiple traditional systems potentially supplied by different software vendors. To manage this level of complexity, a number of SDLC models or methodologies have been created, such as waterfall, spiral, Agile software development, rapid prototyping, incremental, and synchronize and stabilize.[4]

SDLC can be described along a spectrum of agile to iterative to sequential methodologies. Agile methodologies, such as XP and Scrum, focus on lightweight processes which allow for rapid changes (without necessarily following the pattern of SDLC approach) along the development cycle.[5] Iterative methodologies, such as Rational Unified Process and dynamic systems development method, focus on limited project scope and expanding or improving products by multiple iterations. Sequential or big-design-up-front (BDUF) models, such as waterfall, focus on complete and correct planning to guide large projects and risks to successful and predictable results. Other models, such as anamorphic development, tend to focus on a form of development that is guided by project scope and adaptive iterations of feature development.

In project management a project can be defined both with a project life cycle (PLC) and an SDLC, during which slightly different activities occur. According to Taylor (2004), "the project life cycle encompasses all the activities of the project, while the systems development life cycle focuses on realizing the product requirements".[6]

The SDLC is not a methodology per se, but rather a description of the phases in the life cycle of a software application. In a broad sense, these phases are: investigation, analysis, design, build, test, implement, and maintenance and support. All software development methodologies follow the SDLC phases but the method of doing that varies vastly between methodologies. In the Scrum framework,[7] for example, one could say a single user story goes through all the phases of the SDLC within a single two-week sprint. Contrast this to the waterfall methodology, as another example, where every business requirement (recorded in the analysis phase of the SDLC in a document called the Business Requirements Specification) is translated into feature/functional descriptions (recorded in the design phase in a document called the Functional Specification) which are then all built in one go as a collection of solution features typically over a period of three to nine months, or more. These methodologies are different approaches, yet they both contain the SDLC phases in which a requirement is born, then travels through the life cycle phases ending in the final phase of maintenance and support, after-which the whole life cycle typically starts again for a subsequent version of the software application.

The product life cycle describes the process for building information systems in a very deliberate, structured and methodical way, reiterating each stage of the product's life. The systems development life cycle, according to Elliott & Strachan & Radford (2004), "originated in the 1960s, to develop large scale functional business systems in an age of large scale business conglomerates. Information systems activities revolved around heavy data processing and number crunching routines".[8]

Several systems development frameworks have been partly based on SDLC, such as the structured systems analysis and design method (SSADM) produced for the UK government Office of Government Commerce in the 1980s. Ever since, according to Elliott (2004), "the traditional life cycle approaches to systems development have been increasingly replaced with alternative approaches and frameworks, which attempted to overcome some of the inherent deficiencies of the traditional SDLC".[8]

The system development life cycle framework provides a sequence of activities for system designers and developers to follow. It consists of a set of steps or phases in which each phase of the SDLC uses the results of the previous one.[9][10]

The SDLC adheres to important phases that are essential for developers—such as planning, analysis, design, and implementation—and are explained in the section below. This includes evaluation of the currently used system, information gathering, feasibility studies, and request approval. A number of SDLC models have been created, including waterfall, fountain, spiral, build and fix, rapid prototyping, incremental, synchronize, and stabilize.[11][12] The oldest of these, and the best known, is the waterfall model, a sequence of stages in which the output of each stage becomes the input for the next.[10] These stages can be characterized and divided up in different ways, including the following:[9][10][13][14]

A ten-phase version of the systems development life cycle[9]

• Preliminary analysis: Begin with a preliminary analysis, propose alternative solutions, describe costs and benefits, and submit a preliminary plan with recommendations.

1. Conduct the preliminary analysis: Discover the organization's objectives and the nature and scope of the problem under study. Even if a problem refers only to a small segment of the organization itself, find out what the objectives of the organization itself are. Then see how the problem being studied fits in with them.
2. Propose alternative solutions: After digging into the organization's objectives and specific problems, several solutions may have been discovered. However, alternate proposals may still come from interviewing employees, clients, suppliers, and/or consultants. Insight may also be gained by researching what competitors are doing.
3. Cost benefit analysis: Analyze and describe the costs and benefits of implementing the proposed changes. In the end, the ultimate decision on whether to leave the system as is, improve it, or develop a new system will be guided by this and the rest of the preliminary analysis data.

• Systems analysis, requirements definition: Define project goals into defined functions and operations of the intended application. This involves the process of gathering and interpreting facts, diagnosing problems, and recommending improvements to the system. Project goals will be further aided by analysis of end-user information needs and the removal of any inconsistencies and incompleteness in these requirements.

A series of steps followed by the developer include:[15]

1. Collection of facts: Obtain end user requirements through documentation, client interviews, observation, and questionnaires.
2. Scrutiny of the existing system: Identify pros and cons of the current system in-place, so as to carry forward the pros and avoid the cons in the new system.
3. Analysis of the proposed system: Find solutions to the shortcomings described in step two and prepare the specifications using any specific user proposals.

• Systems design: At this step, desired features and operations are described in detail, including screen layouts, business rules, process diagrams, pseudocode, and other documentation.

Role in system design: client,ux designer, project manager, business analyst, software developer, QA speacialist

• Development: The real code is written here.
• Integration and testing: All the modules are brought together into a special testing environment, then checked for errors, bugs, and interoperability.
• Acceptance, installation, deployment: This is the final stage of initial development, where the software is put into production and runs actual business.
• Maintenance: During the maintenance stage of the SDLC, the system is assessed/evaluated to ensure it does not become obsolete. This is also where changes are made to initial software.
• Evaluation: Some companies do not view this as an official stage of the SDLC, while others consider it to be an extension of the maintenance stage, and may be referred to in some circles as post-implementation review. This is where the system that was developed, as well as the entire process, is evaluated. Some of the questions that need to be answered include if the newly implemented system meets the initial business requirements and objectives, if the system is reliable and fault-tolerant, and if it functions according to the approved functional requirements. In addition to evaluating the software that was released, it is important to assess the effectiveness of the development process. If there are any aspects of the entire process (or certain stages) that management is not satisfied with, this is the time to improve.
• Disposal: In this phase, plans are developed for discontinuing the use of system information, hardware, and software and making the transition to a new system. The purpose here is to properly move, archive, discard, or destroy information, hardware, and software that is being replaced, in a manner that prevents any possibility of unauthorized disclosure of sensitive data. The disposal activities ensure proper migration to a new system. Particular emphasis is given to proper preservation and archiving of data processed by the previous system. All of this should be done in accordance with the organization's security requirements.[16]

In the following diagram, these stages of the systems development life cycle are divided in ten steps, from definition to creation and modification of IT work products:

Not every project will require that the phases be sequentially executed; however, the phases are interdependent. Depending upon the size and complexity of the project, phases may be combined or may overlap.[9]

The systems analysis and design (SAD) is the process of developing information technology systems (ITS) that effectively use hardware, software, data, processes, and people to support the company's businesses objectives. It is a process of planning a new business system or replacing an existing system by defining its components or modules to satisfy specific requirements. System analysis and design can be considered the meta-development activity, which serves to set the stage and bound the problem. SAD can be leveraged to set the correct balance among competing high-level requirements in the functional and non-functional analysis domains. System analysis and design interact strongly with distributed enterprise architecture, enterprise I.T. Architecture, and business architecture, and relies heavily on concepts such as partitioning, interfaces, personae and roles, and deployment/operational modeling to arrive at a high-level system description. This high-level description is then further broken down into the components and modules which can be analyzed, designed, and constructed separately and integrated to accomplish the business goal. SDLC and SAD are cornerstones of full life cycle product and system planning.

Object-oriented analysis (OOA) is the process of analyzing a task (also known as a problem domain), to develop a conceptual model that can then be used to complete the task. A typical OOA model would describe computer software that could be used to satisfy a set of customer-defined requirements. During the analysis phase of problem-solving, a programmer might consider a written requirements statement, a formal vision document, or interviews with stakeholders or other interested parties. The task to be addressed might be divided into several subtasks (or domains), each representing a different business, technological, or other areas of interest. Each subtask would be analyzed separately. Implementation constraints, (e.g., concurrency, distribution, persistence, or how the system is to be built) are not considered during the analysis phase; rather, they are addressed during object-oriented design (OOD).

The conceptual model that results from OOA will typically consist of a set of use cases, one or more UML class diagrams, and a number of interaction diagrams. It may also include some kind of user interface mock-up.

The input for object-oriented design is provided by the output of object-oriented analysis. Realize that an output artifact does not need to be completely developed to serve as input of object-oriented design; analysis and design may occur in parallel, and in practice the results of one activity can feed the other in a short feedback cycle through an iterative process. Both analysis and design can be performed incrementally, and the artifacts can be continuously grown instead of completely developed in one shot.

Some typical (but common to all types of design analysis) input artifacts for object-oriented:

• Conceptual model: Conceptual model is the result of object-oriented analysis, it captures concepts in the problem domain. The conceptual model is explicitly chosen to be independent of implementation details, such as concurrency or data storage.
• Use case: Use case is a description of sequences of events that, taken together, lead to a system doing something useful. Each use case provides one or more scenarios that convey how the system should interact with the users called actors to achieve a specific business goal or function. Use case actors may be end users or other systems. In many circumstances use cases are further elaborated into use case diagrams. Use case diagrams are used to identify the actor (users or other systems) and the processes they perform.
• System Sequence Diagram: System Sequence diagram (SSD) is a picture that shows, for a particular scenario of a use case, the events that external actors generate, their order, and possible inter-system events.
• User interface documentations (if applicable): Document that shows and describes the look and feel of the end product's user interface. It is not mandatory to have this, but it helps to visualize the end-product and therefore helps the designer.
• Relational data model (if applicable): A data model is an abstract model that describes how data is represented and used. If an object database is not used, the relational data model should usually be created before the design, since the strategy chosen for object-relational mapping is an output of the OO design process. However, it is possible to develop the relational data model and the object-oriented design artifacts in parallel, and the growth of an artifact can stimulate the refinement of other artifacts.

Few people in the modern computing world would use a strict waterfall model for their SDLC as many modern methodologies have superseded this thinking. Some will argue that the SDLC no longer applies to models like Agile computing, but it is still a term widely in use in technology circles. The SDLC practice has advantages in traditional models of systems development that lends itself more to a structured environment. The disadvantages to using the SDLC methodology is when there is need for iterative development or (i.e. web development or e-commerce) where stakeholders need to review on a regular basis the software being designed.

A comparison of the strengths and weaknesses of SDLC:

An alternative to the SDLC is rapid application development, which combines prototyping, joint application development and implementation of CASE tools. The advantages of RAD are speed, reduced development cost, and active user involvement in the development process.

The system lifecycle in systems engineering is a view of a system or proposed system that addresses all phases of its existence to include system conception, design and development, production and/or construction, distribution, operation, maintenance and support, retirement, phase-out and disposal.[20]

• Application lifecycle management
• Decision cycle
• IPO model
• Software development methodologies

• Cummings, Haag (2006). Management Information Systems for the Information Age. Toronto, McGraw-Hill Ryerson
• Beynon-Davies P. (2009). Business Information Systems. Palgrave, Basingstoke. ISBN 978-0-230-20368-6
• Computer World, 2002, Retrieved on June 22, 2006 from the World Wide Web:
• Management Information Systems, 2005, Retrieved on June 22, 2006 from the World Wide Web:

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