Information System Analysis Lab 7 ERD entityrelationship diagram

Information System Analysis Lab 7

ERD • entity-relationship diagram is a data modeling technique that creates a graphical representation of the entities, and the relationships between entities.

Components used in the creation of an ERD • Entity – A person, place or thing about which we want to collect and store multiple instances of data. It has a name, which is a noun, and attributes which describe the data we are interested in storing. It also has an identifier.

Components used in the creation of an ERD • Relationship – Illustrates an association between two entities. It has a name which is a verb.

Crow’s foot symbol Ring represent zero Dash represent one Crow’s foot represent many

Chen and Crow’s foot notations One-to-many (1: M) relationship: Chen notation Crow’s foot notation a painter can paint many painting ; each painting is painted by one painter

Chen and Crow’s foot notations many-to-many (M: N) relationship: Chen notation Crow’s foot notation an Employee can learn many skills; each skill can be learned by many employees.

Chen and Crow’s foot notations one-to-one(1: 1) relationship: Chen notation Crow’s foot notation an Employee can manages one store; each store is managed by one employee.

Chen and Crow’s foot notations

Using Visio to Draw ERD

• A student fills a seat. This is a 1: 1 relationship. 1 student can fill a maximum of 1 seat can be filled by a maximum of 1 student. • A student takes a course. This is a M: M relationship. One student can take many courses, and one course can be taken by many students. -a student must take at least one course, and a course must be taken by at least one student. • An instructor teaches a course. This is a 1: M relationship. One instructor can teach many courses, but one course can only be taught by one instuctor. – an instructor must teach at least 1 course, and a course must be taught by 1 instructor.

• Starting a New Database Model Diagram Choose File, New, Database Model Diagram

• Starting a New Database Model Diagram To set the modeling options you want to use, choose Database, Options, Document

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ERD Using Visio