INFS1000 Lec 5 Data ERD Modelling

Question 1

What are the 4 steps in creating an ERD?

Answer 1

1. Identify entities (business objects you need to store info about).
2. Identify business rules (relationships).
3. Define relationships and represent cardinality (some business objects are actually relationships / associative entities).
4. Identify attributes (characteristics of entities).

Question 2

What are the 3 types of nouns that we discard?

Answer 2

1. Nouns that can be calculated (e.g. revenue).
2. Nouns that only have 1 instance (e.g. Amazon).
3. Nouns that are really attributes / verbs (e.g. gender).

Question 3

What is a UNARY relationship?

Answer 3

Relationship between 2 diff instances of the same entity.

e.g. employee supervises other employees.

Question 4

What is a database application FORM used for?

Answer 4

Used to read, insert, modify, and delete data via a use-friendly interface.

Question 5

What is a database application QUERY used for?

Answer 5

• Means of getting answers from database data.

* Queries feeds into reports

Question 6

What is a database application REPORT used for?

Answer 6

• Shows data in structured format.
• Computes values (e.g. median).
• Used for analysing data (e.g. average age of customers).

Question 7

Why would you use an EXTENDED composite primary key? (M:M)

Answer 7

Extend the composite primary key (e.g. with time) to allow for multiple transactions between same subject and object (e.g. hotel guest + room) OVER TIME.

Question 8

Why would you use a CLASSIFYING relationship? (1:M)

Answer 8

Use a TYPE relationship when an attribute isn’t unique to each entity instance, but to a class (type) of entities.

You can then assign certain attributes to the TYPE (e.g. Rate as an attribute of ROOM TYPE), and others to the object (e.g. floor for ROOM).