Page 201 - DCAP507_SYSTEM_SOFTWARE

Unit 12: Formal Systems and Programming Languages

12.4 Summary Notes

 A formal system comprises a formal language and a set of inference rules.
 Formal methods are system design methods that use thoroughly declared mathematical
models to construct software and hardware systems. In distinction to other design systems,
formal methods use mathematical evidence as a match to system testing so as to make
sure correct behavior.
 Formal methods vary from other design systems via the use of formal verification systems.
 Throughout the formal specification phase, the engineer thoroughly defines a system by
means of a modeling language.
 A formal specification is a requirement articulated in a language whose vocabulary, syntax
and semantics are formally defined.
 Large specifications are rigid to understand so it is significant that a specification language
comprises structuring facilities which permit specifications to be developed incrementally.

 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 grammar is a set of rules by which applicable sentences in a language are created.

12.5 Keywords

Formal System: A formal system comprises a formal language and a set of inference rules.
Formal Specification: A formal specification is a requirement articulated in a language whose
vocabulary, syntax and semantics are formally defined.

Grammar: A grammar is a set of rules by which applicable sentences in a language are created.
Here's a trivial example of English grammar.
Specification: 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.

12.6 Review Questions

1. What are formal systems? Illustrate the use of formal systems in programming languages.
2. Elucidate the steps included in formal design.

3. Discuss why formal methods are only being slowly acknowledged by engineers.
4. What is formal specification? Illustrate with example.
5. Illustrate the advantages and disadvantages of formal specification.
6. Enlighten the Pre and Post-Conditions used in formal specification.
7. What is grammar? Give an example of an English grammar.

8. Define a grammar for strings where the number of a's is equal to the number b’s.
9. Define a grammar where the number of a's is not equal to the number b’s.
10. Explain the concept of Parse Representation with example.

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