17 - Refinements All design involves refinement-moving from...

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Refinements All design involves refinement--moving from a high-level understanding to an implementation Multiple layers may be involved (not just two) depending on the complexity of the problem To execute a multilayer design properly, three properties must obtain: 1. The top layer must faithfully represent the requirements 2. Each layer must be internally consistent 3. Each lower layer must faithfully represent the layer above it
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Valid Refinements Designer needs to demonstrate that the design satisfies the requirements specification This demonstration can be expressed using a set of verification conditions, sometimes called proof obligations The demonstration itself can be formal or informal depending on the process used
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Exercise • Assumptions – The requirements are expressed as a UML analysis model – We are using OCL for specification – We are concerned with the specification of a single class ( A ) – We are only concerned with functional requirements Question 1 – What should our specification of this class include?
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Exercise • Assumptions – The requirements are expressed as a UML analysis model – We are using OCL for specification – We are concerned with the specification of a single class ( A ) – We are only concerned with functional requirements Question 1 – What should our specification of this class include? – Attributes (types, sizes, properties, etc.) – Operations (signatures, pre/post conditions) – Invariants over the attributes
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Exercise - 2 Property 1 states that our specification for class A must match the requirements – Question: How would we normally accomplish this?
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