e-r modeling steps

The Entity Relationship Model has describe some following steps are available here. There are

  1.  Identify the entity
  2. Identify the attribute
  3. Find the relationship
  4. Identify other relevant attribute
  5. Draw complete E-R Diagram with all attribute including primary key

For understating these steps complete we   take a example of a college database ..

 

 

  • A collage have a many departments
  • Each department has many courses
  • Many instructor are working here
  • An instructor work in only one department
  • For each department has  a one head
  • A course can be taken by only one instructor
  • A student can enroll for any number of course
  • Each Course can have any number of course

Steps 1.– Identify the entity

  • Department
  • Student
  • Course
  • Instructor

These are the entity.

Step 2– Identify the attribute

  • Department is the key attribute for the Entity “Department” as it identifies the department uniquely.
  • Course is the key attribute for  “course ” entity
  • Student is the key attribute for ” student ” entity.
  • Instructor name is the key attribute for ” instructor” entity

Steps 3- Find the relationships –

  • One course is enrolled by multiple student and one student enrolls for multiple course, Hence cardinality between course and student is many to many.
  • The department offer many course and each course belong to only one department hence the cardinality between department and course is one to many.
  • One department has multiple instructors and one instructor belongs to one and only one department hence the cardinality between department and instructor is one to many.
  • Each department there is a “head of department ” and one instructor is ” Head of department” hence the relationship is one to one.
  • One course is taught by only one instructor,but the instructor teaches many courses hence the cardinality between course and instructor is many to one.

Step 4- Identify other relevant attribute-

  • For the department entity the relevant attribute is location.
  • for course entity course name ,duration,prerequisite.
  • For instructor entity Room,mobile.
  • For student entity. student name ,student id ,date of birth etc.

 

 

 

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