1. E.R Diagrams Tiffany Shaw 6AQ‘

2. What is an E.R Diagram?
An entity –Relationship Diagram (E.RD ) is a tool that graphically show the connections among entities in a system. An entity is an object in the system that has data. For eg. A cybercafé might have customer, order, menu item, computer and vendor entities.

3. What are the symbols used in ERD?
1 2 3
1. Define Entities: these are usually nouns used in descriptions of the system, in the discussion of business rules, or in documentation;
entity
. Define Relationships: these are usually verbs used in descriptions of the system or in discussion of the business rules (entity ______ entity);
Identifying relationships
An attribute is a property or descriptor of an entity, for example, Customer Name is an attribute of the entity Customer.
Attrbute

4. What is a one-to-one relationship?
A diagram that show only one matching record in a table
School
Student

5. What is a one-to-many relationship
This relationship is most common as a record in a table have many matching records.
School Board
student
teacher

6. What is a many to many relationship?
Records may have many matching records in one table in relation to the other tables
law
math
M.Ho
K.Ken