Software Engineering Chapter 10 Formal Specification Ku-Yaw Chang [email protected] Assistant Professor Department of Computer Science and Information

Software EngineeringSoftware Engineering

Chapter 10Chapter 10Formal SpecificationFormal Specification

Ku-Yaw ChangKu-Yaw [email protected]@mail.dyu.edu.tw

Assistant ProfessorAssistant ProfessorDepartment of Computer Science and Information EngineeringDepartment of Computer Science and Information Engineering

Da-Yeh UniversityDa-Yeh University

22Ku-Yaw ChangKu-Yaw Chang Formal SepcificationFormal Sepcification

ObjectivesObjectives

Understand why formal specification techniques help Understand why formal specification techniques help discover problems in system requirements;discover problems in system requirements;

Understand the use of algebraic techniques of formal Understand the use of algebraic techniques of formal specification to define interface specifications;specification to define interface specifications;

Understand how formal, model-based formal techniques Understand how formal, model-based formal techniques are used for behavioral specfication.are used for behavioral specfication.


PreamblePreamble

Traditional engineering disciplinesTraditional engineering disciplines Mathematical analysisMathematical analysis

A routine part of the process of developing and validating a A routine part of the process of developing and validating a product designproduct design

Software engineering has not followed the same Software engineering has not followed the same pathpath Formal methods are not widely usedFormal methods are not widely used


PreamblePreamble

Formal methodsFormal methods Mathematical representation of softwareMathematical representation of software Expressed in a language whose vocabulary, syntax Expressed in a language whose vocabulary, syntax

and semantics are formally definedand semantics are formally defined

Most software developments do not use formal Most software developments do not use formal methodsmethods Successful software engineeringSuccessful software engineering Market changesMarket changes

Quality vs. time to marketQuality vs. time to market Limited scope of formal methodsLimited scope of formal methods Limited scalability of formal methodsLimited scalability of formal methods


ContentsContents

10.1 Formal specification in the software process10.1 Formal specification in the software process

10.2 Sub-system interface specification10.2 Sub-system interface specification

10.3 Behavioral specification10.3 Behavioral specification


Formal SpecificationFormal Specification

Formal specificationFormal specification After system requirementsAfter system requirements Before detailed system designBefore detailed system design A tight feedback loop betweenA tight feedback loop between

the detailed requirements specificationthe detailed requirements specification

the formal specificationthe formal specification

One of the main benefitsOne of the main benefits Ability to uncover problems and ambiguities in the Ability to uncover problems and ambiguities in the

system requirementssystem requirements


Specification and DesignSpecification and Design

Increasing contractor involvement

Decreasing client involvement

Specification

Design

Userrequirements

definition

Systemrequirementsspecification

Architecturaldesign

Formalspecification

High-leveldesign


Formal SpecificationFormal Specificationin the Software Processin the Software Process

Systemrequirementsspecification

Formalspecification

High-leveldesign

Userrequirements

definition

Systemmodelling

Architecturaldesign


Software Development CostsSoftware Development Costswith Formal Specificationwith Formal Specification

Specification

Specification

Design andimplementation

Design andimplementation

Validation

Validation

Cost



Two fundamental approachesTwo fundamental approaches An algebraic approachAn algebraic approach

In terms of operations and their relationshipsIn terms of operations and their relationships A model-based approachA model-based approach

A model is built using mathematical constructsA model is built using mathematical constructs



Different languagesDifferent languages


ContentsContents





Sub-system Interface SpecificationSub-system Interface Specification

A large systemA large system Be decomposed into sub-systemsBe decomposed into sub-systems

Sub-systems make use of other sub-systemsSub-systems make use of other sub-systems

Define sub-system interfacesDefine sub-system interfaces An essential part of the specification processAn essential part of the specification process Sub-systems can be designed and implemented Sub-systems can be designed and implemented

independentlyindependently Clear and unambiguous sub-system interface Clear and unambiguous sub-system interface

specificationsspecifications


Sub-system Interface ObjectsSub-system Interface Objects

Interfaceobjects

Sub-systemA

Sub-systemB


Structure of an Object SpecificationStructure of an Object Specification

IntroductionIntroduction Defines the sort (the type name) and declares other Defines the sort (the type name) and declares other

specifications that are used.specifications that are used.

DescriptionDescription Informally describes the operations on the type.Informally describes the operations on the type.

SignatureSignature Defines the syntax of the operations in the interface and their Defines the syntax of the operations in the interface and their

parameters.parameters.

AxiomsAxioms Defines the operation semantics by defining axioms which Defines the operation semantics by defining axioms which

characterize behavior.characterize behavior.


The Structure ofThe Structure ofan Algebraic Specificationan Algebraic Specification

sort < name >imports < LIST OF SPECIFICATION NAMES >

Informal description of the sort and its operations

Operation signatures setting out the names and the types ofthe parameters to the operations defined over the sort

Axioms defining the operations over the sort

< SPECIFICATION NAME >


A Simple List SpecificationA Simple List Specification

Head (Create) = Undefined exception (empty list)Head (Cons (L, v)) = if L = Create then v else Head (L)Length (Create) = 0Length (Cons (L, v)) = Length (L) + 1Tail (Create ) = CreateTail (Cons (L, v)) = if L = Create then Create else Cons (Tail (L), v)

sort Listimports INTEGER

Defines a list where elements are added at the end and removedfrom the front. The operations are Create, which brings an empty listinto existence, Cons, which creates a new list with an added member,Length, which evaluates the list size, Head, which evaluates the frontelement of the list, and Tail, which creates a list by removing the head fromits input list. Undefined represents an undefined value of type Elem.

Create ListCons (List, Elem) ListHead (List) ElemLength (List) IntegerTail (List) List

LIST ( Elem )


ContentsContents




The EndThe End

Documents

Software Engineering Chapter 10 Formal Specification Ku-Yaw Chang [email protected] Assistant Professor Department of Computer Science and Information