Database Management System_ER Model.docx

Database Management System_ER Model.docx - Database...

Info icon This preview shows pages 1–3. Sign up to view the full content.

Database Management System | ER Model ER Model is used to model the logical view of the system from data perspective which consists of these components: Entity, Entity Type, Entity Set An Entity may be an object with a physical existence – a person, car, house, or employee – or it may be an object with a conceptual existence – a company, a job, or a university course. An Entity is an object of Entity Type and set of all entities is called as entity set. e.g.; E1 is an entity having Entity Type Student and set of all students is called Entity Set. In ER diagram, Entity Type is represented as: Attribute Attributes are the properties which define the entity type . For example, Roll_No, Name, DOB, Age, Address, Mobile_No are the attributes which defines entity type Student. In ER diagram, attribute is represented by an oval. Key Attribute The attribute which uniquely identifies each entity in the entity set is called key attribute. For example, Roll_No will be unique for each student. In ER diagram, key attribute is represented by an oval with underlying lines. Composite Attribute An attribute composed of many other attributes is called as composite attribute. For example, Address attribute of student Entity type consists of Street, City, State, and Country.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

In ER diagram, composite attribute is represented by an oval comprising of ovals. Multival ued Attribute An attribute consisting more than one value for a given entity.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.
  • Fall '14
  • rani
  • Entity-relationship model, entity, Course Entity

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern