Jan 21, 200291. 3913 Ron McFadyen1 Ch 10. Domain Model: Visualizing Concepts Domain model illustrated with a class diagram (with no operations defined)

Jan 21, 2002 91. 3913 Ron McFadyen 1

Ch 10. Domain Model: Visualizing Concepts

Domain model

• illustrated with a class diagram (with no operations defined)

• emphasis on real-world objects

• a visual dictionary

• a map of concepts in a domain

• contains

• (conceptual) classes from the problem domain

• associations

• attributes

Jan 21, 2002 91. 3913 Ron McFadyen 2


Domain model

• Bottom of Page 138

•“ … the most common mistake when creating a domain model is to represent something as an attribute when it should have been a concept. “

If we do not think of some conceptual class X as a number or text in the real world, X is probably a conceptual class, not an attribute.

Jan 21, 2002 91. 3913 Ron McFadyen 3

Identifying conceptual classes

Linguistic analysis

• identify the nouns present in Use Cases and other descriptions

Using analysis patterns (advanced)

• Analysis Patterns, Fowler 1995

• Data Model Patterns, Hay 1996 Read th

ese books

(next y

ear or s

o)

Jan 21, 2002 91. 3913 Ron McFadyen 4

Identifying Classes

Books and journals The library contains books and journals. It may have several copies of a given book. Some of the books are for short term loans only. All other books may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals.

Borrowing The system must keep track of when books and journals are borrowed and returned, enforcing the rules described above

Noun Identification

Jan 21, 2002 91. 3913 Ron McFadyen 5

Identifying Classes - candidate list

library

book

journal

copy of a given book

short term loan

library member

week

Member of the library

item

time

member of staff

system

rule

discard - outside scope

discard - not an object (yet, anyway)

discard - redundant see “Members of the library”

discard - not a thing (here)

discard - too vague, turns out to be book or journal

discard - outside scope

discard - part of the meta-language, not part of the domain

discard - part of the meta-language

Jan 21, 2002 91. 3913 Ron McFadyen 6

Identifying Classes - result

book

journal



member of staff

Domain Classes

The domain is the application area we are working in

These classes describe our problem space

Natural classes from the problem space the user can appreciate

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Identifying Objects - result

book

journal



member of staff

Class Diagram

We can place these in a diagram and illustrate how they are related by creating the appropriate associations

Jan 21, 2002 91. 3913 Ron McFadyen 8

A Class Diagram

Book

CopyLibraryMember

MemberOfStaff Journal

0..1 0..*

0..1 0..*

1..*

1is a copy of

borrows/returns

borrows/returns

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Flight

destination

arrival

vsFlight

destination

arrival

Airport

Destination and arrival airports as attributes

Destination and arrival airports as assocations

Preferred

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Specification (Description) conceptual classes

P. 142: Include a specification class when

• we need a description of something irrespective of its existence

• deletions result in loss of information

• it reduces duplicated information

Sale

SaleLineItem ProductSpecification

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Specification (Description) conceptual classes - Airline Example

Flight is a class that keeps track of flight number, date and time for a flight, departure and arrival airports.

departs from

arrives in arrival

departure

*

* 11

Flight

numberdatetime

nameaddress

Regardless of the date/time of a flight, the number and the airports involved stay constant.

Airport

Jan 21, 2002 91. 3913 Ron McFadyen 12

Specification (Description) conceptual classes - Airline Example

Flight

datetime

Larman suggests the use of a Description/Specification Conceptual Class to hold these attributes

- to avoid an anomaly relating to information disappearing due to objects being deleted.

FlightDescription

number*

1

departs from

arrives in arrival

departure

*

* 11

nameaddress

Airport

Jan 21, 2002 91. 3913 Ron McFadyen 13

Page 164:

• Focus on those associations for which knowledge of the relationship needs to be preserved for some duration

• “need-to-know” associations

• Avoid showing redundant or derivable associations

Associations

• correspond to verbs expressing a relationship between classes• objects do not exist in isolation - they fit together in some way

Jan 21, 2002 91. 3913 Ron McFadyen 14

“need-to-know” associations

Flight

datetime

Our database needs to record, to keep track of, when flights are scheduled, where they fly from and to - I.e. we need to know (or be able to derive) this information.

FlightDescription

number*

1

departs from

arrives in arrival

departure

*

* 11

nameaddress

Airport

Jan 21, 2002 91. 3913 Ron McFadyen 15

no redundant associations

departs from

arrives inarrival

departure

Flight

datetime

nameaddress

We can always derive the departure and arrival airports for a flight, so we don’t need to have these 2 redundant relationships

AirportFlightDescription

number*

1

*

*

1

1

arrival

departure

Jan 21, 2002 91. 3913 Ron McFadyen 16

*

0..1

Page 158: “ a person can be Married-to only one other person at any particular moment, even though ...

Person

is Married to

?

Multiplicity

Jan 21, 2002 91. 3913 Ron McFadyen 17

*

0..1

Page 158: “ the car is only Stocked-by one dealer ...

Car

Stocked-by

?

Dealer

Multiplicity

Jan 21, 2002 91. 3913 Ron McFadyen 18

1

0..1

Page 159: “ … The answer depends on our interest in using the model ...

Store

Stocks

?

Item

Multiplicity

*

Jan 21, 2002 91. 3913 Ron McFadyen 19

Page 160:

?0..11Person

Supervises

Multiplicity

*

Jan 21, 2002 91. 3913 Ron McFadyen 20

• Pages 156, 162: “association checklist”• typical ways in which associations arise

• A is physically contained in B … Section in a Book

• A is an organizational subunit of B … Faculty in a University

• etc

Associations

Jan 21, 2002 91. 3913 Ron McFadyen 21

P. 165 :

Larman indicates that some of these may not be needed

- not really part of the requirements

- may not need-to-know all that are shown here

Associations

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• attributes are preferably primitive (or just data types)

boolean, date, number, string, ...

Invoice

invDate: date

Attributes

Jan 21, 2002 91. 3913 Ron McFadyen 23

• Non-primitive types• where the associated things don’t need to be distinguished, such as phone number, quantities, points …•the abstraction makes sense in the problem domain

• a phone number has many parts• an item number that has subparts in its encoding• price is a Currency• amount is a Currency• qty_ordererd is a Quantity• these make sense in the problem domain• price * qty_ordered makes sense

Attributes

Jan 21, 2002 91. 3913 Ron McFadyen 24

•An Invoice will have a grand total•Each Invoice Line will have a quantity ordered and a subtotal

InvLineamount: Currencyqty_ordered: Quantity

Quantity

amount: Number

InvoiceinvDate: dateamount: Currency

Attributes

Currency

amount: Number

Jan 21, 2002 91. 3913 Ron McFadyen 25

Page 172: No Foreign Keys as attributes in the Domain Model• foreign keys are considered later in design

• example: an Invoice is not shown with an attribute for Customer; that is handled by the association between Customer and Invoice

Invoice

invDate: date

Customer

name: stringaddress: string

Attributes

Jan 21, 2002 91. 3913 Ron McFadyen 26

Page 175: Derived attributes

• the UML notation is to prefix the attribute with a /

SalesLineItem

/quantity/subtotal

Item1..*0, 1

In this case, according to the model, there could be several items related to one line in the sale. These items are all the same type, and the quantity is therefore derivable by counting the number of related items. We are just adding more information to the model.

Attributes

Jan 21, 2002 91. 3913 Ron McFadyen 27

Video

ID

Stocks

Rents

Rents-from

11..*

1 *1*

VideoStore

addressnamephoneNumber

Customer


Video store example

Jan 21, 2002 91. 3913 Ron McFadyen 28

VideoRental

dueDatereturnDatereturnTime

CashPayment

amount : Money

Video

ID

Stocks

Rents

Rents-from

Pays-for

Initiates

11

1..*

1

1

1

1..*

1 *1*

RentalTransaction

date1

* *

VideoStore


Customer


1

Records-rental-of

0..1

1

Video store example

More detail added:

Jan 21, 2002 91. 3913 Ron McFadyen 29

titlesubjectCategory

Video

ID


Where do we keep track of the title or other descriptions for things like the videos that are rented?

?

Jan 21, 2002 91. 3913 Ron McFadyen 30

Catalog

VideoDescription

titlesubjectCategory

Video

ID

Stocks

Owns-a

Described-by

1

1

*

1

1

1

* *

1..*

VideoStore


1


VideoDescription is a class that keeps track of the title and subject category for videos.

Documents

Jan 21, 200291. 3913 Ron McFadyen1 Ch 10. Domain Model: Visualizing Concepts Domain model illustrated with a class diagram (with no operations defined)