{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

ch6 - Chapter 6 Entity-Relationship Model Chapter Database...

Info icon This preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Database System Concepts, 5th Ed . ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Chapter 6: Entity-Relationship Model Chapter 6: Entity-Relationship Model
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
©Silberschatz, Korth and Sudarshan 6.2 Database System Concepts - 5 th Edition, Oct 5, 2006 Chapter 6: Entity-Relationship Model Chapter 6: Entity-Relationship Model Design Process Modeling Constraints E-R Diagram Design Issues Weak Entity Sets Extended E-R Features Design of the Bank Database Reduction to Relation Schemas Database Design UML
Image of page 2
©Silberschatz, Korth and Sudarshan 6.3 Database System Concepts - 5 th Edition, Oct 5, 2006 Modeling Modeling A database can be modeled as: a collection of entities, relationship among entities. An entity is an object that exists and is distinguishable from other objects. Example: specific person, company, event, plant Entities have attributes Example: people have names and addresses An entity set is a set of entities of the same type that share the same properties. Example: set of all persons, companies, trees, holidays
Image of page 3

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

View Full Document Right Arrow Icon
©Silberschatz, Korth and Sudarshan 6.4 Database System Concepts - 5 th Edition, Oct 5, 2006 Entity Sets Entity Sets customer customer and and loan loan customer_id customer_ customer_ customer_ loan_ amount name street city number
Image of page 4
©Silberschatz, Korth and Sudarshan 6.5 Database System Concepts - 5 th Edition, Oct 5, 2006 Relationship Sets Relationship Sets A relationship is an association among several entities Example: Hayes depositor A-102 customer entity relationship set account entity A relationship set is a mathematical relation among n 2 entities, each taken from entity sets {( e 1 , e 2 , … e n ) | e 1 E 1 , e 2 E 2 , …, e n E n } where ( e 1 , e 2 , …, e n ) is a relationship Example: (Hayes, A-102) depositor
Image of page 5

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

View Full Document Right Arrow Icon
©Silberschatz, Korth and Sudarshan 6.6 Database System Concepts - 5 th Edition, Oct 5, 2006 Relationship Set Relationship Set borrower borrower
Image of page 6
©Silberschatz, Korth and Sudarshan 6.7 Database System Concepts - 5 th Edition, Oct 5, 2006 Relationship Sets (Cont.) Relationship Sets (Cont.) An attribute can also be property of a relationship set. For instance, the depositor relationship set between entity sets customer and account may have the attribute access-date
Image of page 7

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

View Full Document Right Arrow Icon
©Silberschatz, Korth and Sudarshan 6.8 Database System Concepts - 5 th Edition, Oct 5, 2006 Degree of a Relationship Set Degree of a Relationship Set Refers to number of entity sets that participate in a relationship set. Relationship sets that involve two entity sets are binary (or degree two). Generally, most relationship sets in a database system are binary. Relationship sets may involve more than two entity sets. Relationships between more than two entity sets are rare. Most relationships are binary. (More on this later.) Example: Suppose employees of a bank may have jobs (responsibilities) at multiple branches, with different jobs at different branches. Then there is a ternary relationship set between entity sets employee, job, and branch
Image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the 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