2. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Learning Objectives
• State why domain modelling is done
• List the steps in Noun Phrase Approach for finding
candidate classes
• Apply the technique to find candidate classes
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3. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Domain Modelling
• What is a “domain”?
– Area of interest
– Area of the problem to be
solved
• Domain Modelling
– Modelling (to represent) the
business domain (problem
domain)
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4. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Why Perform Domain Modelling?
• Define the key concepts for the problem
domain.
– Also called candidate classes
• Identify and relate the key abstractions (key
classes / ideas) that the system must handle:
these candidate classes will be used to later
analyse and design the use case.
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5. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Conceptual/ Domain Modelling
• Two step process involving:
– Step 1: Find Candidate Classes
• Noun-Phrase Approach / Noun Analysis
– underline the noun(s) in the problem description and decide if they are
relevant and key to solving the problem)
– Step 2: Complete the domain model
• Add attributes
• Add relationships between classes
• Draw the classes, attributes and relationships on a class diagram.
• Domain Modelling captures:
• Candidate classes
• Attributes of candidate classes
• Relationships
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6. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Noun Phrase Approach
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Finding candidate classes
(Noun phrase approach)
Complete the
domain model
We are here
Domain modelling
7. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Noun Phrase Approach
• What are Nouns?
– A word that can be used to refer to a person, place,
thing, quality.
– Examples:
• Customer, Sale, ShoppingCart, Student, Movie, Teacher
– Noun with one or more other words.
– Example: "The black cat is happy."
• noun phrase: "the black cat"
– Noun/Class Cat
– Attribute Black
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8. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
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Exercise 1: Find the Nouns
• Given the following statement:
“All students in OOAD are fans of Mr. Bean and
watch his shows on their Laptops.”
• Find the nouns.
9. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Noun Phrase Approach (Steps)
• Read the documents, look for noun phrases, and make a list of nouns
• Divide the list of nouns into these categories:
– Relevant (Candidate Class).
– Fuzzy (we are not sure).
– Irrelevant.
– Attributes.
• Write a statement of purpose for each noun.
– For what purpose do you want to “store” this data?
– For irrelevant nouns, there's no reason for having them.
• For those in the “Relevant” and “Fuzzy” categories, write possible attributes
relevant to the domain
– If no attributes, the class is irrelevant
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10. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Guidelines for Class Identification
• Avoid computer implementation classes.
– Example: AccountDB_table
• too DB implementation specific
• If there are two classes with similar meaning, keep only one
(which is most meaningful).
– Subject & Course may have the same meaning
• If there is a class that is “relevant”, but does not map to a
concept in the system re-write it as an attribute
– Name, age are not classes but attributes of another class
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11. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
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Exercise 2: Apply Noun Phrase Approach
• Given the following statement:
“School ABC wants to track the number of hours each
student spends in the lab. A student using the lab has
his/her matric number and date stored. Each lab has a
number and location.
A weekly report is generated showing the number of
hours spent by each student per lab.”
• Use the Noun Phrase Approach to identify the candidate
classes for the domain of this lab usage system. Use the
noun phase analysis template.
12. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
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Noun-Phrase Analysis Template
Noun/Noun
Phrase
Statement of
purpose
Possible Attributes Classification Accept
(Y/N)
Reason for
Rejection
Partial Noun phrase approach to identify
candidate classes: (one row per noun you find)
Write “Relevant”,
“Fuzzy”,
“Irrelevant”, or
“Attributes”
Write the
noun
Write the
possible
attributes
Y(es) – accept
As candidate
class
13. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Food for Thought
• What are the steps in the noun phrase
approach?
• What are the categories in which we divide
our list of nouns?
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14. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
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Guidelines for Class Identification (1)
• Classes adorned with adjectives:
– Does the object represented by the noun behave
differently when the adjective is applied to it?
– If the use of the adjective signals that the behaviour of
the object is different, then make a new class.
– Example:
• If AdultMember and YouthMember behave differently or
contain several different properties, then they should be
classified as different classes.
15. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
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Guidelines for Class Identification(2)
• Irrelevant Classes:
– Each class must have a purpose and every class should be
clearly defined when necessary.
– If you cannot come up with a statement of purpose, simply
eliminate the candidate class.
– Example: If you are designing a computer system for the
school, and there is only 1 school, which is the Domain
environment for the system, we do not need to have School
class.
16. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
Naming Classes guidelines (3)
• Guidelines for Naming Classes
– The class should describe a single object, so it should be the singular form
of noun.
• Example: "Student" is correct; "Students" is wrong
– Use names that the users are comfortable with.
– The name of a class should reflect its intrinsic nature.
– Use readable names. By convention, the class name must begin with an
Upper-case letter.
– For compound words, capitalize the first letter of each word.
• Example: PartTimeStudent, FullTimeStudent.
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17. TEMASEK POLYTECHNIC • SCHOOL OF INFORMATICS & IT
The fate of candidate classes
• As we move from Requirements (domain
modelling is considered a requirements
analysis technique) to Use Case Analysis and
Use Case Design, we may discover more
classes, and we may also refine attributes
and add operations to our existing candidate
classes.
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