UML and WSDL for JISC e-Learning Projects INTRODUCTION TO UML Richard Hopkins [email protected] NeSC Training Team Member [email protected].

UML and WSDL for JISC e-Learning Projects

INTRODUCTION TO UML

Richard Hopkins [email protected]

NeSC Training Team Member

JISC UML/WSDL – Introduction to UML, 9th Nov. 2004 2

Goals and Overview

Goals –To enable you to understand the UML part of the first example To explain the context and overall approach for UML

OverviewUML History and conceptsSimple use of most essential diagrams

Requirements Structure Behaviour


History of UML

Use of diagramsIn any discipline for the construction of complex artefactsNeed to use diagrams, as tools for

Thinking Communicating

As discipline matures, diagrams become - Standardised – For effective communication between all practitioners Stylized – Specialised technical language for compact representation

UML – M is for ModelsA diagram is a model of the (proposed) systemA partial representation of some aspect of the system


History of UML

Historically A variety of stylised diagram languagesEach associated with a design methodology

A formalised Process for arriving at a design

E.g., for Object-oriented design (early 90’s) Grady Booch’s OOD – Object-Oriented Design James Rumbaugh’s OMT – Object-oriented Modelling and Design Ivar Jacobson’s OOSE – Object-Oriented Software Engineering

Competing MethodologiesRather improbably –

Rumbaugh joined Booch, with intention of merging their methods

They bought out Jacobsonn’s company – Objectory These three aimed for a single Unified Method


Methodolgy vs Notation

Generally need different methodologies for different contexts

Small application in four weeks by single programmerLarge system in four years by 200-strong development organisation

Often “use of X methodology” was actuallyuse of “X’s”notation with methodology appropriate to context

Strong reasons for using the same notation

Concept of Unified Method, changed to Unified Modelling Language


Methodology vs Notation

UML is NOT a methodologyUML is a notation for recording the results of

A requirements gathering / design processCarried out using some methodology – maybe!

Any kind of diagram can be used for any purpose that is useful

Sufficiently general that could be used with any imaginable O-O methodology

However, for concreteness we will assume a particular general methodology -


An Overall Development Process

Partially articulated requirements

Capture Requirements

Use Case Diag. Requirements

ConstructModel of

Overall system Class Diag. Structure

Sequence Diag. Behaviour

These diagram types, and the process can be used both forDesigning a new systemUnderstanding an existing system


Requirements




Introducing the Library Example

A computer system for a university library; some “facts”

The library has members –StaffStudents

The library contains items -Books

possibly several copies of each book Some books are for short-term loan only – only students can do short-term loans

Journals Only staff may borrow journals

The functionalities includeKeeping track of when items are borrowed/returnedAllow users to search for a book and check availability


Some Queries

The library has members –StaffStudents

The library containsBooks;

possibly several copies of each book Some books are for short-term loan only – only students can do short-

term loans

Journal Only staff may borrow journals

The functionalities includeKeeping track of when items are borrowed/returnedAllow users to search for a book and check availability

Can someone be both?

Do we mean copies?

Is “user” something different from “member?Henceforth use “user”


Requirements Engineering

Natural language statement of requirements is typically riddled with ambiguities and inconsistencies

Requirements Engineering is the discipline of dealing with this

Developing UML models helps with identifying and clarifying requirements

But still depends on natural language documentation

It helps, but does not guarantee complete consistent set of requirements


Requirements - Simple Use Cases

An Actor –a user of the system, in a particular role

“BookBorrower” is a role played by library membersUsually a person, but could be another system

An entity outside the system being modelledIn web services – usually another web service

BookBorrower

Borrow Copy of book

UpdateCatalogue

Librarian

A Use Case –A task that an actor needs to perform with the help of the system“Borrow Copy of Book” describes the successful outcome – there will be variants for the exception cases -

This Actor participates in this Use Case


Simple Use Cases

Not a very rich diagram – later on we will see richer diagramsNeeds more explanation – associated documentation

Limitations of natural language!

BookBorrower

Borrow Copy of book

Use Case Documentation

Use Case: Borrow copy of book.

• A bookBorrower presents a book.

• The system checks that the potential borrower is a member of the library,

• and that s/he does not already have the maximum permitted number of books on loan.

• The maximum is 6 unless the member is is a staff member, in which case it is 12.

• If both ckecks succeed, the system records that this library member has this copy of the book on loan.

• Otherwise it refuses the loan.

UpdateCatalogue

Librarian


STRUCTURE




Structure - Class Design

UML is for Object-Oriented DesignThe state of the system is a collection of ObjectsEach Object is an instance of a ClassThe structure of the system is characterised by the class and their inter-relationships

Key is identifying the classeskinds of things manipulated within the system

Standard Technique - Noun identification

Take a concise description of the systemIdentify the words/phrases that denote things


Noun Identification

Some Facts –

The library contains books and journals.

It may have several copies of a given book.

The system must keep track of when items are borrowed and returned

The system must allow users to borrow items subject to rules –

A student can borrow up to six items …


Class Design – Which Nouns?Library

Book

Journal

Item

System

Rule

User

Student

☺

NO – Not “within the system”

Yes if rules are updatable

No if rules are built in

Yes – All these are things which the system needs to trackAlthough they are not independent – Journal is a special case of item Student is a special case of user

Here a “book”, “student” etc. within the system – Represents an actual entity in the external world Partially Tracks what is happening to the real world entity

☺

☺

☺

☺


Class Diagram

A box for each ClassThere are relationships between classes

Otherwise don’t need a diagram!!!

User

Student Staff

Item

Journal Book

Specialisation/GeneralisationUser is a generalisation of both

Student Staff

Any instance of Student is also an instance of User

Student

Later we will see other class relationships


Class Attributes and Operations

Book

Title : String

Item

Journal

Attribute – Information associated with each instance of the class –

what’s important for understanding; not all that exists in a programming language class implementing it

Each attribute will have a type


Class Attributes and Operations

Book

Title : String

copiesOnShelf() : Integer

Item

Journal

An operation – something that instances of this class can do, which can be externally invoked

A unit of functionality which is externally exposedEquivalent to a Java Method

copiesOnShelf() : IntegerTo provide the invoker with a number which is the number of copies of the book which are available for borrowing.

copies(in onShelf:Bool, out copyNos[0..*] Integer) : Status

UML terminology is message-passing - An object’s operation is invoked by another object sending it a message


Web Services as Objects

A WSDL definition corresponds to a class “a service type”

An actual web service conforming to that definition is an instance of that classBut service types are often not found by “noun identification”

Often more byIdentifying Functions, rather than things

Legacy Overall domain understanding (guesswork / intuition) Notion of layered architecture

Viewing a function-provider as a service object


Example some Web ServicesA Web services Framework for E-learning (surprise!)

User Agents (layer)

Portal Timetabling Library Authoring Tool . . .

Application Service (layer)

Group Management Resource Discovery Resource Management . . .

Common Services (layer)

. . .Authentication Authorisation Search Messaging

Naturally a domain noun? –YesNo

(As perceived by domain non-expert!)


BEHAVIOUR




Behaviour - Sequence Diagrams

To Document how objects work together to achieve an overall function of the system –

An Interaction Diagram

Each sequence diagram shows an example “walk-through”

Typically for a use case

Not for all of themFor

Complex situations Where clarification seems needed


Sequence Diagram - participants

For Use Case : Borrow copy of book

BookBorrower

theUser: User theCopy: Copy theBook: Book

Identify the participantsExternal Actor from the use caseObjects within the system

This is an instance diagram –

Name each object, and identify its classtheUser – object which is the internal representation of the user playing the BookBorrower role“theUser : User” seems redundant, but could have several User participants


Sequence Diagram – LifelinesBookBorrower


time

Object existence lifeline Period of activation

1:

3:2:

4:

1. BookBorrower invokes the use case – activating the corresponding User object, theUser

2. theUser tells theCopy object that it is now borrowed – it changes its state3. theCopy tells theBook that it has been borrowed – its reduces its count of

available copies4. TheUser confirms success to BookBorrower

The replies to 2 and 3 not shown because not particularly important, whereas the confirmation to external user is.

Sending a message

The reply


Sequence Diagram – Operations

BookBorrower


time

Object existence lifeline Period of activation

1: borrow(theCopy)

3: borrowed()2: borrow()

4: borrowStatus

Associate with the message line –The information communicatedUsually the operation invoked and possibly its parameters

Sending a message

The reply


Final PointsUML is a language to enable expression

Its up to you what you express and what you don’t

Which cases you give sequence diagramsWhich attributes you include for a class. . .

Based on maximising usefulness to the reader

Rather than rigid rules

Butit maybe you organisation’s standards, rather than your personal judgement

UML and WSDL for JISC e-Learning Projects INTRODUCTION TO UML Richard Hopkins [email protected] NeSC Training Team Member [email protected].

Documents

methodology uml

uml overview uml history

jisc umlwsdl introduction

history of uml use of

methodology vs notation

compact representation

developing uml models

use case slide