Page 196 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes 12.2.8 The Use of Structure

 Large specifications are rigid to understand so it is significant that a specification language
comprises structuring facilities which permit specifications to be developed incrementally.

12.2.9 Theoretical Aspects: Formally

 A formal specification language is a triple:
< Syn, Sem, Sat >
where Syn and Sem are sets and Sat, a subset of Syn X Sem, is a relation between them.
 Syn is called the language's syntactic domain, Sem is the semantic domain and Sat is the
satisfies relation.
 Given a specification language,
<Syn, Sem, Sat>

 if Sat(syn,sem) then syn is a specification of sem and sem is a specific and of syn.
12.2.10 Theoretical Aspects: Less Formally

 A formal specification language offers
 A notation (its syntactic domain),
 A universe of objects (its semantic domain), and
 A precise rule defining which objects satisfy each requirement.

 A specification is a sentence written in terms of the elements of the syntactic domain; it
indicates a specific and set, a subset of the semantic domain.
 A specific and is an object pleasing a specification – the satisfies relation offers the meaning
for the syntactic elements.

Example: An Example of a Simple Specification Language
 Backus-Naur form:
 syntactic domain  a set of grammars
 semantic domain  a set of strings

 Every string is a particular and of each grammar that produces it.
 Every specific and set is a formal language.

Self Assessment

Fill in the blanks:
6. A ................................ is a requirement articulated in a language whose vocabulary, syntax
and semantics are formally defined.
7. ................................ conditions are predicates over the inputs and outputs of a function.
8. The specification language, Z (pronounced 'zed') uses ................................ to structure
specifications.

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