The Systems Development Life Cycle is the big picture of creating an information system that handles a major task (referred to as an application). The applications usually consist of many programs. An example would be the Department of Defense supply system, the customer system used at your local bank, the repair parts inventory system used by car dealerships. There are thousands of applications that use an information system created just to help solve a business problem.
Another example of an information system would be the "101 Computer Games" software you might buy at any of several retail stores. This is an entertainment application, that is we are applying the computer to do a task (entertain you). The software actually consists of many different programs (checkers, chess, tic tac toe, etc.) that were most likely written by several different programmers.
Computer professionals that are in charge of creating applications often have the job title of System Analyst. The major steps in creating an application include the following and start at Planning step.
During the Design phase the System Analyst will document the inputs, processing and outputs of each program within the application. During the Implementation phase programmers would be assigned to write the specific programs using a programming language decided by the System Analyst. Once the system of programs is tested the new application is installed for people to use. As time goes by, things change and a specific part or program might need repair. During the Maintenance phase, it goes through a mini planning, analysis, design and implementation. The programs that need modifcation are identifed and programmers change or repair those programs. After several years of use, the system usually becomes obsolete. At this point a major revision of the application is done. Thus the cycle repeats itself.