Data Modeling and the Entity-Relationship Model

-Degree 3 = ternary relationship 1:1(one-to-one-A single...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Three Stages of Database Development - Requirements Analysis Stage - Component Design Stage - Implementation Stage All a part of the Systems Development Life Cycle (SDLC) model What are the most important elements of E-R Models? - Entities - Attributes - Identifiers - Relationships What is an entity class? - Description of the structure and format of the occurrences of the entity. What is an entity instance? - A specific occurrence of an entity within an entity class. Attributes - Entities have attributes that describe the entity’s characteristics. - ProjectName, StartDate, ProjectType, ProjectDescription - Attributes have a data type and properties. Identifiers - Identifies a particular instance in the entity class. - SocialSecurityNumber - StudentID - EmployeeID - Identifiers may be unique or nonunique. - A composite identifier consists or two or more attributes. Relationships - Entities can be associated with one another in relationships. - Relationship degree defines the number of entity classes participating in the relationship. - Degree 2 = binary relationship
Image of page 1

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

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: -Degree 3 = ternary relationship 1:1 (one-to-one)-A single entity instance in one entity class is related to a single entity instance in another entity class. -An employee may have no more than one locker; and a locker may only be accessible by one employee. 1:N (one-to-many)-A single entity instance in one entity class is related to many entity instances in another entity class. -A quotation is associated with only one item; and an item may have several quotations. N:M (many-to-many)-Many entity instances in one entity class is related to many entity instances in another entity class. -A supplier may supply several items; and a particular item may be supplied by several suppliers. Cardinality-Relationships are named and classified by their cardinality, count.-Maximum cardinality = max number of entity instances that may participate in a relationship instance. -Minimum cardinality = minimum number of entity instances that must participate in a relationship instance....
View Full Document

{[ 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