{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

lecture-11-designing-er-diagrams

lecture-11-designing-er-diagrams - Design Constraints...

Info icon This preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Design Constraints Entity-Relationship Models: Good Design and Constraints T. M. Murali September 29, 2010 T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
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
Design Constraints Guidelines I Be faithful to the specification of the application. I Avoid redundancy. I Keep the entities and relationship simple. I Select the right relationships. I Select the right type of element. T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
Image of page 2
Design Constraints Be Faithful I Do not use meaningless or unnecessary attributes. I Define the multiplicity of a relationship appropriately. I What is the multiplicity of the relationship Take between Students and Courses ? I What is the multiplicity of the relationship Teach between Professors and Courses ? T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
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
Design Constraints Avoid Redundancy I Redundancy occurs when we express the same fact in two or more ways. I Redundancy wastes space. I Redundancy can lead to inconsistency if we change one instance but not the other. T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
Image of page 4
Design Constraints Select the Right Relationships I Do not add unnecessary relationships. I It may be possible to deduce one relationship from another. T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
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
Design Constraints Select the Right Relationships I Do not add unnecessary relationships. I It may be possible to deduce one relationship from another. I Do we need the relationship Instruct between Professors and Students ? Students Courses Professors Take Teach Instruct T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
Image of page 6
Design Constraints Select the Right Relationships I Do not add unnecessary relationships. I It may be possible to deduce one relationship from another. I Do we need the relationship Instruct between Professors and Students ? I No. We can deduce this relationship from Take and Teach . Students Courses Professors Take Teach Instruct T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
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
Design Constraints Select the Right Relationships I Do not add unnecessary relationships. I It may be possible to deduce one relationship from another. I Do we need the relationship Instruct between Professors and Students ? I No. We can deduce this relationship from Take and Teach . I Do we need the relationships Take and Teach ? Courses Students Evaluation Professors Take Teach T. M. Murali September 29, 2010 CS 4604: E/R Design and Constraints
Image of page 8
Design Constraints Select the Right Relationships I Do not add unnecessary relationships.
Image of page 9

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

View Full Document Right Arrow Icon
Image of page 10
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