E.R Diagrams Tiffany Shaw 6AQ ‘

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.

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

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

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

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