Page 194 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes  Animation of a specification to offer a prototype system, and mathematical study.
 Formal specs may be used as a conduct to the creation of test cases for any specific component
of the system.

12.2.2 Disadvantages of Formal Specifications

 Software management is intrinsically conservative and is unwilling to adopt new
techniques if the payoff is not instantly obvious.

 Most analysts and programmers have not been skilled in formal specification techniques.
 Clients are not probable to be recognizable with formal specifications and may be unwilling
to fund expansion activities that they do not understand and thus cannot control.

 Some classes of systems are still complicated to specify by means of current techniques.
 There is widespread unawareness of existing specification techniques and their uses.
 Most research efforts have been directed at the expansion of notations and not with tool support.

12.2.3 Notations

 Notations like VDM involve the use of a number of particular symbols which must be
memorized and this leads to a important learning curve.
 Some notations include a mnemonic notation that is less alien and can be typed in by
means of a standard keyboard.

 The specification language, Z (pronounced 'zed') uses graphics to structure specifications.
 This enhances its readability and encourages incremental growth of specifications.

12.2.4 Developing a Simple Formal Specification

 The simplest form is axiomatic specification where a system is signified as a set of functions
(which are stateless), and

 This technique is at present used only for small systems or system components.

!
Caution Each function is specified using pre and post-conditions.

12.2.5 Pre and Post-Conditions

 These conditions are predicates over the inputs and outputs of a function.
 A predicate is just a boolean expression which is true or false and whose variables are the
parameters of the function being specified.

 Predicates include:
 operators (like =, >, <, not, and, or),
 the universal and existential quantifiers, and
 the operator in which is used to choose the range over which the quantifier applies.

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