1. Domain Model: Visualizing Concepts
Ch. 9

2. Domain Models
A Domain Model illustrates meaningful concepts in a problem domain.
Does a domain model represent real things or SW components?
Is a domain model static or interactive?
It may show:
concepts
associations between concepts
attributes of concepts
Avoid Analysis Paralysis!
Domain Model <> Class Diagram!
DM: representation of real-situation conceptual classes not of sw objects == Visual dictionary, shows abstraction of conceptial classes

3. Domain Models
A Domain Model is a description of things in the real world.
A Domain Model is not a description of the software design.
What is a concept?
Item
Store * 1
address
name
Stocked-in

4. Conceptual Classes in the Sale Domain
What is the distinction between OO and structured analysis?
Store
POS
Sale
Partial Domain Model.
Symbol: words or image
Intention: definition
Extension: examples to which conceptual class applies

5. Strategies to Identify Conceptual Classes
Use a conceptual class category list.
Use noun phrase identification.
Why create domain model? Domain layer supports a mental layer between our mental model of the domain, lower representation gap with OO, DM inspires objects and names in OO, reduce representational gap: use actual objects and definitions to inspire coding objects and class blueprints

6. Use a conceptual class category list
Concept Category Example
Physical or tangible objects POS
Specifications, designs, or
descriptions of things ProductSpecification
Places Store
Transactions Sale, Payment
Transaction line items SalesLineItem
Roles of people Cashier
Containers of other things Store, Bin
(See complete list in Larman 2nd. ed., pp )

7. Finding Conceptual Classes with Noun Phrase Identification
1. This use case begins when a Customer arrives at a POS checkout with items to purchase.
2. The Cashier starts a new sale.
3. Cashier enters item identifier. …
How to: find nouns, draw as classes, add associations, attributes
Do not reinvent the wheel

8. The Need for Specification or Description Conceptual Classes
What is wrong with this picture?
Consider the case where all items are sold, and thus deleted from the computer memory.
How much does an item cost?
Item
description
price
serial number
itemID

9. The Need for Specification or Description Conceptual Classes
The memory of the item’s price was attached to inventoried instances, which were deleted.
Notice also that in this model there is duplicated data (description, price, itemID).
Item
description
price
serial number
itemID

10. The Need for Specification or Description Conceptual Classes
When should we add a specification or description concept?
ProductSpecification
description
price
itemID 1
Describes *
Conceptual classes – categories, noun phrase identification,
Item
serial number

11. The NextGen POS (partial) Domain Model
Item
Store
Sale
Sales
LineItem
Cashier
Customer
Manager
Payment
Product
Catalog
Product
Specification

12. Adding Associations “Direction reading arrow” has no meaning
other than to indicate direction of reading
the association label.
Optional (often excluded)
POS
Records-current
Sale
Association: relationship between classes, meaningful, interesting connection, preserved for some duration, between what models do wen need a memory of a relationship “need to remember”. NOT a statement about data flows!
Paths of navigation and visibility
ClassName – VerbPhrase - ClassName 1 1
Association name

13. Finding Associations –Common Associations List
Category Examples
A is a physical part of B* Drawer - POS
A is a logical part of B SalesLineItem - Sale
A is physically contained in/on B POS - Store
A is logically contained in B ItemDescription - Catalog
A is a description of B ItemDescription - Item
A is a line item of a transaction
or report B SalesLineItem - Sale
A is known/logged/recorded/
captured in B Sale - POS
A is a member of B Cashier - Store
...
(See complete list in Larman 2nd. ed.,
pp )
* High-priority associations

14. Multiplicity Store Stocks Item 1 * Multiplicity *: zero or more
Multiplicity: how many instances of class A can be associated with an instance of class B

15. Multiplicity * T Zero or more; “many” 1..* T One or more 1..40 T
One to forty 5 T
Exactly five
3, 5, 8 T
Exactly three, five
or eight.

16. Naming Associations
Store
Name an association based on a TypeName-VerbPhrase- TypeName format.
Association names should start with a capital letter.
A verb phrase should be constructed with hyphens.
The default direction to read an association name is left to right, or top to bottom. 1
Contains
1..*
POS 1
Captures
1..*
Paid-by
Sale
Payment 1 1

17. Multiple Associations Between Two Types
It is not uncommon to have multiple associations between two types.
In the example, not every flight is guaranteed to land at an airport.
Flies-to
0..1 *
Flight
Airport
Flies-from * 1

18. Adding Attributes Sale date startTime: Time Attributes
Attribute: logical data value of an object
Visibility name: type multiplicity – default [property-string]
/ derived attribute: calculated
-, +: private, public
Domain model: no types of attributes!
Guidelines for modeling data types: represent smt as a new data type class in domain model if:
It is composed of separate sections
Operations associated with it
Has other attributes
Is quantity with unit
It is an abstraction

19. Valid Attribute Types Cashier Not a simple attribute name
currentRegister
Cashier
Register
name
uses
number 1 1

20. Domain Model Conclusion
Records-sale-of 1
0..1
Described-by *
Product
Catalog
Product
Specification
Sales
LineItem
Contains
description
price
itemID 1
1..*
quantity 1
Used-by
1..* *
Describes
1..*
Store
Item 1 *
Contained-in
Logs-completed
address
name
Stocks 1 * 1 *
Sale 1
Houses
1..*
date
time
Captured-on
POS
Manager
Started-by 1 1 1 1
Conclusion: is DM correct? Yes if it captures the essential abstractions and information required. Avoid waterfall mindset of analysis paralysis, limit domain modeling to a few hrs per iteration 1 1
Paid-by
Initiated-by 1 1 1
Records-sales-on
Payment
Customer
Cashier 1
amount