An object type is identified by a noun and in some cases it may be strong or weak entity class. A Strong object type is represented by a triangle and a weak entity class by a triangle inside another triangle. Attributes collectively represent the object class. Attributes by themselves are meaningless and cannot clearly define themselves. In the Visio diagrams, they are usually symbolized by an oval.
Attributes are what is stored in the database hence gives a clear view of how the database would appear. Example: student has a student Id, name and course. In the above example, student is the entity class and student Id, name and course are attributes. Some attributes have a primary key. The key is preferably composed of only a single attribute, but in some cases, more than one.
The final element of entity relation diagram is the relationship. Entities have relationships between them and should be represented where appropriate. Relationship are represented by a diamond and two connecting lines.
Business rule is a statement that imposes some constraint on some particular aspect of the database. You base a business rule based on the organization views and usage of its data, which you determine from the way in which the body performs or conducts its affairs.
Ways of doing things are unique and has different requirements in each group. An example is a club having more than one student and the student not being a member of more than one club. Therefore, there is a constraint on the student’s membership on a given number of clubs (Andreescu & Mircea, 2012).
First, the course can have more than one student partaking it and more than one student can be part of the course. It means, many students will be taking a course, and a student can also do many courses.
Secondly, more than one student can be taught by an instructor, and only one instructor can teach many students.