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 symbolRing represent zeroDash represent oneCrow’s  foot represent many

Chen and Crow’s foot notations One-to-many (1:M) relationship:

a painter can paint many painting ;each painting is painted by one painter

Chen notation Crow’s foot notation

Chen and Crow’s foot notations many-to-many (M:N) relationship:

an Employee can learn many skills; each skill can be learned by many employees.

Chen notation Crow’s foot notation

Chen and Crow’s foot notations one-to-one(1:1) relationship:

an Employee can manages one store; each store is managed by one employee.

Chen notation Crow’s foot notation

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. 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, Database Model Diagram

Starting a New Database Model Diagram

• To set the modeling options you want to use, choose Database, Options, Document

Format line

ERD Using Visio