程序代写代做代考 Java Software Construction & Design 1

Software Construction & Design 1

The University of Sydney Page 1

Software Design and

Construction 2

SOFT3202 / COMP9202

Software Verification

Theory and Examples

School of Information Technologies

Dr. Basem Suleiman

The University of Sydney Page 2

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Agenda

– Software Verification Theory

– Design by Contract
– Pre-conditions and post-conditions

– Class invariants

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Software Validation and

Verification

Theory

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Software Testing – Revisit

– Software process to
– Demonstrate that software meets its requirements (validation testing)

– Find incorrect or undesired behavior caused by defects/bugs (defect testing)
• E.g., System crashes, incorrect computations, unnecessary interactions and data

corruptions

– Part of software verification and validation (V&V) process

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Software Verification and Validation

– Software testing is part of software Verification and Validation (V&V)

– The goal of V&V is to establish confidence that the software is “fit for purpose”

– Software Validation
– Are we building the right product?

– Ensures that the software meets customer expectations/needs

– Software Verification
– Are we building the product right?

– Ensures that the software meets its stated functional and non-functional

requirements

The University of Sydney Page 7

Software V&V

– Software Verification
– Concerned with the software requirements/specifications

– Can be ambiguous

– Software Validation
– Customer/end user’s expectation

– Disambiguate the requirements

The University of Sydney Page 8

V-Model

– Link each phase of the SDLC with its associated testing phase

– Each verification stage relates to a validation stage

https://www.buzzle.com/editorials/4-5-2005-68117.asp

https://www.buzzle.com/editorials/4-5-2005-68117.asp

The University of Sydney Page 9

Software Verification

– Artifact/specification verification
– Review the resulted software artifacts to verify that specifications are met

– Check the output of each software development phase against the input

specification (specs.)

– Design specifications against requirement specifications
• Detailed design correctly implement the requirements (F & NF)

– Construction (code) against the design specs.
• Source code/user interfaces correctly implements the design specs.

– Include inspections, reviews, walkthrough

The University of Sydney Page 10

Static Verification

– Static Verification

– Static system analysis to discover problems

– May be applied to requirements, design/models, configuration and test data

– Reviews

– Walk through

– Code inspection

The University of Sydney Page 11

Software Validation

– Artifact/specification validation
– Validate the requirements from the end user perspective

– Check that the needs of all stakeholders (users, managers, investors) are met
– Validate the output of main development stages from the stakeholder’s point of

view

• Validate if the requirements represent the will and goals of the

stakeholders

– Include Unit testing, integration/functional testing, and user acceptance

testing

The University of Sydney Page 14

Design by Contract

The University of Sydney Page 15

Contract

– A lawful agreement between two parties in which both
parties accept obligations and on which both parties can
found their rights

– The remedy for breach of a contract is usually an award of
money to the injured party

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Object-Oriented Contract

– Specifies the expected services that can be provided if
certain conditions are satisfied

– Services = “Obligations” and conditions = “Rights”

– Breach of a contract results in generating an exception

The University of Sydney Page 17

Design by Contract (DbC)

– A software design approach for program correctness

– Known as contract programing, programming by contract,
design-by-contract programming

– Definition of formal, precise and verifiable interface
specification for software components

– Pre-conditions, postconditions and invariants (contract)

The University of Sydney Page 18

Design by Contract (DbC)

By Fabuio [CC0], from Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Design_by_contract.svg

https://commons.wikimedia.org/wiki/File:Design_by_contract.svg

The University of Sydney Page 19

Contracts in OO Design

Object-oriented contract

– Describes the services that are provided by an object if
certain conditions are fulfilled

– services = “obligations”, conditions = “rights”

– An OO-contract for each service specifically describes:
– The conditions under which the service will be provided

– A specification of the result of the service that is provided

– The remedy for breach of an OO-contract is the generation
of an exception

The University of Sydney Page 20

Object-Oriented Contract –

– Examples:
– A letter posted before 18:00 will be delivered on the next working day

to any address within Australia

– For the price of $7 a letter with a maximum weight of 80 grams will be
delivered anywhere in Australia within 4 hours of pickup

– Exercise: identify the conditions/rights and obligations/services of the
above delivery services.

The University of Sydney Page 21

Modeling Constraints

with Contracts

The University of Sydney Page 23

Modeling Constraints with Contracts

– Example of constraints in Arena:
– An already registered player cannot be registered again

– The number of players in a tournament should not be more than
maxNumPlayers

– One can only remove players that have been registered

– We model them with contracts

– Contracts can be written in OCL

The University of Sydney Page 24

Modeling OO-Contracts – Formal Specifcation

– Natural Language

– Mathematical Notation

– Models and contracts:
– A language for the formulation of constraints with the formal strength

of the mathematical notation and the easiness of natural language:

 UML + OCL (Object Constraint Language)

– Uses the abstractions of the UML model

– OCL is based on predicate calculus

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Contracts and Formal Specification

– A Contract share same assumptions about the class

– Three constraints:
– Invariant:

• A predicate that is always true for all instances of a class

– Precondition (“rights”):

• Must be true before an operation is invoked

– Postcondition (“obligation”):

• Must be true after an operation is invoked.

The University of Sydney Page 26

Formal Specification

– A contract is called a formal specification, if the invariants,
rights and obligations in the contract are unambiguous

The University of Sydney Page 27

Expressing Constraints in UML Models

HashTable

put(key,entry:Object)
get(key):Object
remove(key:Object)
containsKey(key:Object):boolean
size():int

numElements:int

<>
numElements >= 0<>

!containsKey(key)

<>
containsKey(key)

<>
containsKey(key)

<>
!containsKey(key)

<>
get(key) == entry

The University of Sydney Page 28

Use Contracts in Requirements Analysis

– Many constraints represent domain-level information

– Why not use them in requirements analysis?

– Increase requirements precision

– Yield more questions for the end user

– Clarify the relationships among several objects

– Constraints are sometimes used during requirements
analysis, however there are trade-offs

The University of Sydney Page 30

Object Constraint

Language (OCL)

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Object Constraint Language (OCL)

– Formal language for expressing constraints over a set of objects and their
attributes

– Part of the UML standard

– Used to write constraints that cannot otherwise be expressed in a diagram

– Declarative

– No side effects

– No control flow

– Based on Sets and Multi Sets

The University of Sydney Page 32

OCL Basic Concepts

– OCL expressions

– Return True or False

– Are evaluated in a specified context

– All constraints apply to all instances

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Example – Tournament Class

Tournament

– maxNumPlayers: int

+ acceptPlayer(p:Player)

+ removePlayer(p:Player)

+ getMaxNumPlayers():int

+ getPlayers(): List

+ isPlayerAccepted(p:Player):boolean

The University of Sydney Page 34

OCL Simple Predicates

“The maximum number of players in any tournament should be a
positive number.”

context Tournament inv: self.getMaxNumPlayers() > 0

Notes:

– OCL uses the same dot notation as Java

The University of Sydney Page 35

OCL Preconditions – Examples

“The acceptPlayer(p) operation can only be invoked if player p has not yet
been accepted in the tournament.”

context Tournament::acceptPlayer(p) pre:

not self.isPlayerAccepted(p)

Questions:

– What is the context the pre-condtion?

– What is “isPlayerAccepted(p)”?

The University of Sydney Page 36

OCL Postconditions – Example

“The number of accepted player in a tournament increases by one after
the completion of acceptPlayer()”

context Tournament::acceptPlayer(p) post:

self.getNumPlayers() =

self@pre.getNumPlayers() + 1

Notes:

– self@pre: the state of the tournament before the invocation of the operation

– self: denotes the state of the tournament after the completion of the operation

The University of Sydney Page 37

OCL Contract for acceptPlayer() in Tournament

context Tournament::acceptPlayer(p) pre:

not isPlayerAccepted(p)

context Tournament::acceptPlayer(p) pre:

getNumPlayers() < getMaxNumPlayers() context Tournament::acceptPlayer(p) post: isPlayerAccepted(p) context Tournament::acceptPlayer(p) post: getNumPlayers() = @pre.getNumPlayers() + 1 The University of Sydney Page 38 OCL Contract for removePlayer() in Tournament context Tournament::removePlayer(p) pre: isPlayerAccepted(p) context Tournament::removePlayer(p) post: not isPlayerAccepted(p) context Tournament::removePlayer(p) post: getNumPlayers() = @pre.getNumPlayers() - 1 The University of Sydney Page 39 Java Implementation of Tournament class (Contract as a set of JavaDoc comments) public class Tournament { /** The maximum number of players * is positive at all times. * @invariant maxNumPlayers > 0

*/

private int maxNumPlayers;

/** The players List contains

* references to Players who are

* are registered with the

* Tournament. */

private List players;

/** Returns the current number of

* players in the tournament. */

public int getNumPlayers() {…}

/** Returns the maximum number of

* players in the tournament. */

public int getMaxNumPlayers() {…}

/** The acceptPlayer() operation

* assumes that the specified

* player has not been accepted

* in the Tournament yet.

* @pre !isPlayerAccepted(p)

* @pre getNumPlayers()includes(p)

The University of Sydney Page 47

OCL Sets, Bags and Sequences

– Sets, Bags and Sequences are predefined in OCL
– Subtypes of Collection

– OCL offers a large number of predefined operations on
collections. All of the form:

collection->operation(arguments)

The University of Sydney Page 48

OCL-Collection

– The OCL-Type Collection is the generic superclass of a collection of objects
of Type T

– Subclasses of Collection are

– Set: Set in the mathematical sense. Every element can appear only once

– Bag: A collection, in which elements can appear more than once (also called
multiset)

– Sequence: A multiset, in which the elements are ordered

– Example for Collections:

– Set(Integer): a set of integer numbers

– Bag(Person): a multiset of persons

– Sequence(Customer): a sequence of customers

The University of Sydney Page 49

OCL-Operations for OCL-Collections (1)

size: Integer

Number of elements in the collection

includes(o:OclAny): Boolean

True, if the element o is in the collection

count(o:OclAny): Integer

Counts how many times an element is contained in the collection

isEmpty: Boolean

True, if the collection is empty

notEmpty: Boolean

True, if the collection is not empty

The OCL-Type OclAny is the most general OCL-Type

The University of Sydney Page 50

OCL-Operations for OCL-Collections(2)

union(c1:Collection)
Union with collection c1

intersection(c2:Collection)
Intersection with Collection c2 (contains only elements, which appear in the collection as
well as in collection c2 auftreten)

including(o:OclAny)
Collection containing all elements of the Collection and element o

select(expr:OclExpression)
Subset of all elements of the collection, for which the OCL-expression expr is true

The University of Sydney Page 51

Evaluating OCL Expressions
The value of an OCL expression is an object or a collection of objects.

– Multiplicity of the association-end is 1

– The value of the OCL expression is a single object

– Multiplicity is 0..1

– The result is an empty set if there is no object, otherwise a single object

– Multiplicity of the association-end is *

– The result is a collection of objects

• By default, the navigation result is a Set

• When the association is {ordered}, the navigation results in a
Sequence

• Multiple “1-Many” associations result in a Bag

The University of Sydney Page 52

OCL Quantifiers

forAll

– forAll (variable|expression) is True if expression is True for all
elements in the collection

exist

– exists (variable|expression) is True if there exists at least one
element in the collection for which expression is True

The University of Sydney Page 53

OCL Quantifiers – forAll Example

Given the following OCL quantifier

context Tournament inv:

matches->forAll(m:Match |

m.start.after(t.start) and m.end.before(t.end))

Exercise: explain what this OCL attempts to verify.

The University of Sydney Page 55

OCL Quantifiers – Exists Example

Given the following OCL quantifier

context Tournament inv:

matches->exists(m:Match | m.start.equals(start))

The University of Sydney Page 59

References

– Ian Sommerville. 2016. Software Engineering (10th ed.) Global Edition.
Pearson.

– Wikipedia, Software Verification and Validation,
https://en.wikipedia.org/wiki/Software_verification_and_validation

– Object-Oriented Software Engineering: Using UML, Patterns, and Java, 3rd
Edition, Bernd Bruegge & Allen H. Dutoit, Pearson.

http://vig.prenhall.com/catalog/academic/product/0,4096,0130471100,00.html

The University of Sydney Page 60

W12 Tutorial: Practical

Exercises

Design Pattern Assignment

Demo

W12 Lecture: Specification

Languages

The University of Sydney Page 69

Specifying the Model Constraints: Using asSet

Local attribute navigation

context Tournament inv:

end – start <= Calendar.WEEK Directly related class navigation context Tournament::acceptPlayer(p) pre: league.players->includes(p)

players

* tournaments

{ordered}

Tournament

+start:Date

+end:Date

+acceptPlayer(p:Player)

*

League

+start:Date

+end:Date

+getActivePlayers()

*

Player

+name:String

+email:String

* players

tournaments*

Indirectly related class navigation
context League::getActivePlayers

post:

result=tournaments.players->asSet

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