Lecture 04 DomainModelling 2spp

7/25/2019 Lecture 04 DomainModelling 2spp

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Requirements analysis and

modelling the domain

Software Development Practices

Lecture 4

Where are you at?Assignment #1

Due next week, Wednesday 3rd September at 12:30 pm

Submission via Blackboard Turnitin

Assignment #2

To be released next week, Wednesday afternoon

Group assignment (Group of 3-4 students, from the same

tutorial session)

Form your group early start NOW

Progress will be monitored by your tutor on a weekly basis

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SDP Roadmap

Problem analysis Domain modelling domain diagrams

Modelling behaviour use cases, use case diagrams

Adding detail to domain model class diagrams

Dynamic behaviour sequence, collaboration diagrams

etc

Defining Architecture deployment diagrams

Detailed design wireframes

Testing3

Overview of This Lecture Introduction to Case Studies

Requirement Gathering

Use Case Modeling

Domain Modeling / Business Modeling

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Case Study 1: The Restaurant

Example developed in the Practical Object-Oriented DesignWith UML by Mark Priestley, chapter 4.

Support the day-to-day operations of restaurant by improvingthe processes of:

Making Reservations

Allocating Tables

Current System is based on manual booking system:

Hand-written forms in large folder.

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Case Study 1: The Restaurant Current system uses manual booking sheets.

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Case Study 1: The Restaurant

Three sittings (slots) in an eveningBooking can span more than one slot

Each Booking records:

Contact Name and Phone Number

Annotation made for various events:

Arrival of customer (Cross out record)

Table switch (Arrow to new table)

Cancellation

Time to vacate

Walk-In Customer7

Case Study 1: Restaurant Problems with the manual systems/Pain points:

Slow

Confusing and difficult to read/modifiy

No backup copies

Hard to get useful management data

Goal: Develop an automated computerized version.

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Case Study 2: The Monopoly Game

Chosen because of its familiarity.

A game played almost in every country.

Developed in theApplying UML and Patterns by Craig Larman,

Chapter 3.

The software version will run assimulation:

User starts the simulation by indicating the number of simulated players.

All turns are simulated with result (trace) printed.

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Where are we now?

Requirement

Analysi s &

Design

Implementation

Deployment

Business

Modeling Business Modeling

Understanding the problem domain.


Understanding the requirements.

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Testing


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Requirement: Overview

Early phase of the development.

Inputs:

informal specification.

Activities:

create use case model.

define use cases.

create domain model.

create glossary.

create activity diagram.

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Use Case View

Intended to provide a structured view of the system's functionality.

Description of how users interact with the system.

Supported by UMLuse case diagrams.

Serves as the starting point for all subsequent development.

Three important definitions:

Use Case

Scenario

Actor

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Use Case and Scenarios

Use Case: The different tasks that users can perform while interacting

with the system.

Scenarios aka. Courses of events:

Are particular instances of the use case:

Basic Scenario: normal flow.

Alternative Scenario: optional flow.

Exceptional Scenario: erroneous flow.

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Actor

Roles played by users when interacting with a system, e.g.:

Receptionist (makes bookings);

Head waiter (assigns tables etc).

Individual user may play one or more roles at different times.

Often corresponds to certain level of access, e.g., logging

into Swinburne website as Staff or Student.

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Use Case Diagram

UML diagram to summarize the relationship between actors

and use cases.

Diagram Element:

Actor Communication Use Case

Use Case

Dependency

Inherit(Actor Relationship) Constraints

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Case Study 1: Use Cases A preliminary list of use cases:

1 Record new booking.

2 Cancel a booking.

3 Record customer arrival.

4 Transfer a customer from one table to another.

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Case Study 1: Use Case Diagram

Show use cases, actors and who does what.

System

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Use Cases DescriptionA use case comprises all the possible interactions that a user

can have when performing a given task.

Often a dialogue between system and user.

These are described as scenarios, or courses of events.

A full description of a use case includes:

an actor;

preconditions; success guarantees;

abasic scenario;

a number ofalternative and exceptional scenarios, also calledextensions. 18


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Basic Scenario

Describes what happens in the normal case. For example, for Record Booking:

Record Booking: Basic Scenario

Receptionist enters date of requested reservation;

System displays bookings for that date;

There is a suitable table available: Receptionist enters details

(customers name, phone number, time of booking, number of

covers, table number);

System records and displays new booking.

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Use Case Templates UML does not define a standard format for use case

descriptions.

Various templates have been defined to structure

descriptions.

Essentially a list of subheadings such as:

Name (of the use case)

Actors/goal

Preconditions:

Success guarantees/ postconditions:

Scenarios (basic + extensions)20


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Other Use Case Description Template

1. Receptionist enters date of

requested reservation;

3. there is a suitable table available:

Receptionist enters details

(customers name, phone

number, time of booking, numberof covers, table number);

2. System displays bookings for that

date.

4. System records and displays new

booking.

This version emphasizes the exchange between user andsystem, e.g.:

Actor System

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User Interface Prototype During the use case modeling activity, it is usually useful to have a

rough idea of the user interface, e.g.:

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Al ternat ive Scenarios

Describe predicted alternative flows.

For example, if no table is available:

Record Booking No Table Available: Alternative Scenario

1 Receptionist enters date;

2 System displays bookings;

3 no table available: end of use case.

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Exceptional Scenarios Situations where a mistake has been made.

E.g., allocate a booking to a small table:

Record Booking table too small: Exceptional Scenario

1 receptionist enters date;

2 system displays bookings;

3 receptionist enters details;

4 system asks for confirmation of oversize booking;

5 if no, use case terminates with no booking made;

6 if yes, booking recorded with warning flag.

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Shared Functionality

Different use cases can overlap.

E.g., Record Arrival:

Record Arrival: Basic Scenario

head waiter enters date;

system displays bookings;

head waiter confirms arrival for booking;

system records this and updates display.

First two steps shared with Record Booking (eventhough different actor).

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Use Case Inclusion Move shared functionality to a separate use case:

Record Booking: Basic Scenario (revised)

receptionist performs Display Bookings;

receptionist enters details;

system records and displays new booking.

Include this in other use cases, e.g.:

Display Bookings: Basic Scenario

user enters a date;

system displays bookings for that date.

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The Dependency

UML shows inclusion as a dependency between use cases,labelled with the stereotype on the dashed

arrow:

System

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Case Study 1: Use Case Diagram (Revised)

System

Display

booking

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Actor Generalization

The last diagram shows that the Receptionist can performsthe Display bookings use case independently from the RecordBooking use case.

Head Waiters can also performs Display bookings use case.

Introduce a more general actor Staffto show what the othertwo actors have in common.

The initial actors are specializations of the general actor.

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Actor Generalization Notation

System

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Use Case Extension

Recording a walk-in can be described as an exceptionalcourse of events:

someone arrives but theres no booking recorded.

It could also be a separate use case:

a customer arrives and asks if there's a free table.

Then, it can extend Record Arrival:

even without a booking, the customer stays to eat.

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Use Case ExtensionRecord Walk-in: Basic Scenario:

1 Head waiter performs Display Bookings use case;

2 Head waiter enters details (time, number of covers and the table

allocated to the customer);

3 System records and displays new booking.

Very similar to Record Arrival use case. Can we simplify?

dependency is inappropriate. (why?) Record Walk-in is performed in some cases of Record Arrival,

when there is no booking for the customer.

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The Dependency

Use case extension is shown with a dependency. Record walk-in optionally extends the functionality of Record arrival.

States the constraint (condition) which causes the branch off.

System

No Prior

Booking

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Case Study 1: Complete Use Case Diagram

System

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Guidelines

Use case: Should cover full sequence of steps from the beginning of a task until

the end.

Should describe users interaction with the system.

Should not describeactual computations.

Should be as independent as possible from any particular userinterface design.

Should only include actions in which the actor interacts with thecomputer.

Use case diagram should be used to supplement the use casedescription, not as the main artifact.

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Use Cases: Strengths Simple and Familiar

Can be understood easily by untrained personnel, e.g., the

customer.

Involve the customer early in the development.

Emphasize the user goals and perspective.

Scale in term of sophistication and formality.

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Use Cases: Problems

Care must be taken to ensure the use cases arecomplete and unambiguous.

Only actor initiated activities are recorded.

Software requirement derived from use cases often

mimics the manual system too closely.

Preventing any innovative or more efficient way to be

developed.

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Domain Modelling

Using UML diagram to construct a model of the real-world

system:

Understand the problem domain.

Model recorded as a simplified class diagram.

Seamless development:

The same notation is used for analysis and design.

The design can evolve from the initial domain model.

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Domain Model Notation

A subset of class diagram model elements are used.

Class Name

Attr ibutes

Class

Association

Name

MultiplicityMultiplicity

ClassGeneralization Constraints

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Domain Model Notation Classes represent real-world entities.

At tr ibutes represent the data held about entities.

Associations represent relationships between the entities.

Generalization can be used to simplify the structure of the

model.

Constraints can be used to indicate conditions.

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Case Study 1: Customers and Reservations

Basic business fact: customers make reservations.

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Defining a Relationship Give a name to the relationship:

use a verb so that the relationship can be read as a sentence:

Acustomercanmake many reservations.

How many people make a reservation?

one principal contact whose details are held;

that principal contact can make more than one reservation (e.g., by

postponing the time);

the expected number of diners can be modelled as an attribute of

the reservation.

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Case Study 1: Tables and Reservation

Is table number an attribute of Reservation? Better modelled as a separate class:

tables exist even if there are no reservations;

other attributes of tables, e.g., size, can be stored.Thisimagecannotcurrently bedisplayed.

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Use of Constraints

Not all domain properties can be shown graphically:

e.g., it should be impossible to double-book a table.

Constraints add information to models:

written in a note connected to the model element being

constrained.

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Use of Generalization

A superclass can be used to show the properties shared bydifferent types of booking.

Thisimagecannotcurrently bedisplayed.

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Correctness How do we know when a domain model is complete?

we don't: there are lots of plausible models in most cases.

Domain modelling is not an end in itself, but a guide to

further development.

Realizing use cases tests the domain model, and will

usually lead to refinements.

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Supplementary Documents

Common Supplementary Documentation:Glossary.

Activity Diagram.

Glossary:

Amini dictionary that captures concepts and vocabulary relevant in

the problem domain.

Avoids misunderstanding and facilitate communication.

Activity Diagram

UML diagram that describes activities.

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Case Study 1: Partial Glossary Booking: an assignment of diners to a table.

Covers: the number of diners for a booking.

Customer: a person who makes a reservation.

Reservation: a booking made in advance.

Walk-in: a booking that is not made in advance.

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Summary

Introduction to Case Studies


Use Case Modeling

Domain Modeling / Business Modeling

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References Evans, E. (2004), Domain-driven design : tackling complexity in

the heart of software, Boston, Mass.: Addison-Wesley (LibraryCall Number: 005.1 EVA-D)

Booch et. al. (1998)The unified modelling language user guide,Amazon.com, 2nd edition. (Swinburne library electronic resource)

Larman, C (2006)Applying UML and Patterns, 3rd Ed PrenticeHall

Fowler, M. (2004), UML Distilled: a brief guide to the standardobject modeling language, Addison-Wesley

Simon, B., McRobb, S. & Farmer, R. (2006), Object-orientedsystems analysis and design using UML, London : McGraw-HillEducation, 3rd Edition (Library Call Number: 005.117 BEN-O3)

Bruegge, B & Dutoit, A (2010), OO Software Engineering usingUML, Patterns and Java, 3rdEdition, Prentice Hall

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Lecture 04 DomainModelling 2spp

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Transcript of Lecture 04 DomainModelling 2spp