"In formal methods, refinement is the verifiable transformation of an abstract (high-level) formal specification into a concrete (low-level) executable program. Stepwise refinement allows this process to be done in stages. Logically, refinement normally involves implication, but there can be additional complications. Data refinement is used to convert an abstract data model (in terms of sets for example) into implementable data structures (such as arrays). Operation refinement converts a specification of an operation on a system into an implementable program (e.g., a procedure). The postcondition can be strengthened and/or the precondition weakened in this process. This reduces any nondeterminism in the specification, typically to a completely deterministic implementation."

http://en.wikipedia.org/wiki/Refinement

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Note added at 14 mins (2006-01-30 21:48:46 GMT)
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sau mai bine spus ..."imbunatatiri progrsive"

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Note added at 16 mins (2006-01-30 21:51:09 GMT)
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"imbunatatiri progresive" - typo!