System Integration

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Requirement Specification

A requirement specification is a document that defines what a system should do, what its performance and functional parameters are.

 

It is a kind of order form in that this is what is expected of the system, it is what has been ordered.

 

If you order a pizza you may state that you want a salami and cheese topping with extra tomatoes.  Your requirement can be broken down into 4 specific requirements: -

 

1. A pizza.

2. A salami topping.

3. A cheese topping.

4. Extra tomatoes.

 

The above requirements are the explicit requirements, i.e. the stated requirements.  There are also implicit requirements, i.e. requirements that are not stated but are expected.  Some implicit requirements are: -

 

1. The pizza is hot.

2. The pizza is round in shape.

3. It is within the price range normally expected of a pizza.

4. It is delivered by a waiter who is clean in appearance.

 

Although you have not explicitly stated that that the price range is within a certain band you would expect it to be so and would be justified in rejecting the pizza is, say, you were told it would cost £1000.  You would also be justified in rejecting the pizza if it did not conform to any of the other implied requirements.

 

Just because a requirement is not explicitly stated does not mean it is not a requirement.

 

Just as these implied requirements apply to a pizza they apply to any piece of equipment that is ordered.

 

Some common implied requirements are: -

 

1. It meets all national and international laws.

2. It meets all the conventions expected within the industry, e.g. defense equipment is expected to be of higher quality than equipment in other markets.

3. It can be disposed of, at the end of its life, without excessive expense.

 

The requirement specification is usually at the route of a lot of future system problems, a great deal of attention needs to be given to this document.  Getting the document correct gives any system a solid foundation for future success.