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1. Software Development Life Cycle. The process of developing a software product from conception (the requirements stage) through design, development, testing, release and finally support and maintenance. It is referred to as a cycle because, subsequent releases of a software product will require each one of those stages to be visited.

The Software Development Life Cycle will tend (see note below) the following stages:

  1. Analysis or Requirements specification
    The step of identifying what the software (or software update) needs to do.
  2. Design
    The step of identifying how to meet the requirements.
  3. Implementation or Coding
    The step of doing the work, turning the design into software to meet the requirements.
  4. Testing
    The step of testing the produced software to ensure that it meets the requirements.
  5. Support and Maintenance
    The step of supporting the software once it is being used by end users, identifying and addressing bugs and other issues. This may also lead to new requirements being identified and the software development life cycle beginning again for those new requirements.

There are a number of different software development methodologies and approaches, and each may have different stages (or names for those stages) in the software development life cycle. So the above should only be treated as a guide - all the steps above will (or should) exist regardless of the development methodology but some may be broken into several steps, some may introduce additional steps (for example "Installation and Acceptance") and others may be combined or renamed and the order may be muddled (for example Design and Implementation are often merged in smaller projects).

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2. Systems Development Life Cycle.

An alternative name for "Software Development Life Cycle (SDLC)". Although technically "Systems Development Life Cycle" refers to the development of systems whereas "Software Development Life Cycle" refers to the development of (just) software, the two are generally regarded as synonymous.

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3. Synchronous Data Link Control. A communications protocol developed by IBM. SDLC is a layer 2 protocol (in the OSI 7 layer model).

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