The systems development life cycle (SDLC), also referred to as the application development life-cycle, is a term used in systems engineering, information systems and software engineering to describe a process for planning, creating, testing, and deploying an information system.
The systems development life-cycle concept applies to a range of hardware and software configurations, as a system can be composed of hardware only, software only, or a combination of both.
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.
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".
SDLC can be described along a spectrum of agile to iterative to sequential.
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.
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".
SDLC is used during the development of an IT project, it describes the different stages involved in the project from the drawing board, through the completion of the project.
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.
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. It includes evaluation of present system, information gathering, feasibility study and request approval.
A number of SDLC models have been created: waterfall, fountain, spiral, build and fix, rapid prototyping, incremental, and synchronize and stabilize.
WYCS uses the waterfall model: a sequence of stages in which the output of each stage becomes the input for the next.
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.
These stages can be characterized and divided up in different ways, including the following:
During this step, we must consider all current priorities that would be affected and how they should be handled. Before any system planning is done, a feasibility study should be conducted to determine if creating a new or improved system is a viable solution.
This will help to determine the costs, benefits, resource requirements, and specific user needs required for completion.
The development process can only continue once management approves of the recommendations from the feasibility study.
Following are different components of the feasibility study:
- Operational feasibility
- Economic feasibility
- Technical feasibility
- Human factors feasibility
- Legal/Political feasibility
- System analysis
The goal of system analysis is to determine where the problem is, in an attempt to fix the system. This step involves breaking down the system in different pieces to analyze the situation, analyzing project goals, breaking down what needs to be created and attempting to engage users so that definite requirements can be defined.
In systems design, the design functions and operations are described in detail, including screen layouts, business rules, process diagrams and other documentation. The output of this stage will describe the new system as a collection of modules or subsystems.
The design stage takes as its initial input the requirements identified in the approved requirements document. For each requirement, a set of one or more design elements will be produced as a result of interviews, workshops, and/or prototype efforts.
Design elements describe the desired system features in detail, and generally include functional hierarchy diagrams, screen layout diagrams, tables of business rules, business process diagrams, pseudo-code, and a complete entity-relationship diagram with a full data dictionary. These design elements are intended to describe the system in sufficient detail, such that skilled developers and engineers may develop and deliver the system with minimal additional input design.
Environments are controlled areas where systems developers can build, distribute, install, configure, test, and execute systems that move through the SDLC. Each environment is aligned with different areas of the SDLC and is intended to have specific purposes.
Examples of such environments include the:
Where developers can work independently of each other before trying to merge their work with the work of others.
Common Build Environment
Where merged work can be built, together, as a combined system.
Systems Integration Testing Environment
Where basic testing of a system's integration points to other upstream or downstream systems can be tested.
User Acceptance Testing Environment
Where business stakeholders can test against their original business requirements
Where systems finally get deployed to, for final use by their intended end users.
The code is tested at various levels in software testing. Unit, system and user acceptance testing’s are often performed
The following are types of testing that may be relevant, depending on the type of system under development:
- Defect testing the failed scenarios, including defect tracking
- Path testing
- Data set testing
- Unit testing
- System testing
- Integration testing
- Black-box testing
- White-box testing
- Regression testing
- Automation testing
- User acceptance testing
- Software performance testing
- Training and transition
Once a system has been stabilized through adequate testing, the SDLC ensures that proper training on the system is performed or documented before transitioning the system to its support staff and end users.
Training usually covers operational training for those people who will be responsible for supporting the system as well as training for those end users who will be using the system after its delivery to a production operating environment.
After training has been successfully completed, systems engineers and developers transition the system to its final production environment, where it is intended to be used by its end users and supported by its support and operations staff.
The deployment of the system includes changes and enhancements before the decommissioning or sunset of the system.
Maintaining the system is an important aspect of SDLC. As key personnel change positions in the organization, new changes will be implemented.
There are two approaches to system development; there is the traditional approach (structured) and object oriented.
Information Engineering includes the traditional system approach, which is also called the structured analysis and design technique.
The object oriented approach views the information system as a collection of objects that are integrated with each other to make a full and complete information system.
The final phase of the SDLC is to measure the effectiveness of the system and evaluate potential enhancements.
The picture below shows all the different steps in the SDLC:
Strengths & Weaknesses
The table below show the strengths and weaknesses of following an SDLC: