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After we have built our system, verification and validation

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is that phase of software development that aims to

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check that the software system meets its specification and

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fulfills its intended purpose. More precisely, we can look

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at verification and validation independently. And validation is the

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activity that answers the question did we build the

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right system. Did we build the system that the

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customer wants? That will make the customer happy. Whereas verification

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answers a different question which is did we build the system

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right. So given a description of the system that is the one

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that we derived from the customer through the collection of requirements

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and then design and so on, did we build a system that

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actually implements the specification that we defined? And when we look

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at verification there's many, many ways of doing verification and in fact

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in the mini course number four we will cover verification extensively. The

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only thing I want to mention here is the fact that verification

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can be performed at different levels. In particular, it can be

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performed at the unit level in which we test that the individual

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units work as a expected. Can be performed in the integration level

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in which what we test is the interaction between the different units.

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So we want to make sure that the different modules talk

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to each other in the right way. And finally, there is system

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testing in which we test the system as a whole and we

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want to make sure that all the system, all the different pieces

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of the system work together in the right

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way. And this is also the level at which

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then we will apply validation and some other

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testing techniques like stress testing or robustness testing and

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so on. And as I said I'm not going to say anything more on this topic because

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we will cover verification, and validation, and testing in

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particular in great details in mini course number four.