11 relationship b a a1 a2 a3 b1 b2 b3 mandatory

This preview shows page 44 - 56 out of 125 pages.

We have textbook solutions for you!
The document you are viewing contains questions related to this textbook.
Database Systems: Design, Implementation, & Management
The document you are viewing contains questions related to this textbook.
Chapter 16 / Exercise 7
Database Systems: Design, Implementation, & Management
Coronel/Morris
Expert Verified
1:1 relationship B A A1 A2 A3 B1 B2 B3 Mandatory relationship on both sides: Optional relationship on both sides: B A A1 A2 A3 B1 B2 B3
We have textbook solutions for you!
The document you are viewing contains questions related to this textbook.
Database Systems: Design, Implementation, & Management
The document you are viewing contains questions related to this textbook.
Chapter 16 / Exercise 7
Database Systems: Design, Implementation, & Management
Coronel/Morris
Expert Verified
1:N relationship Mandatory relationship on both sides: Optional relationship on both sides: A1 A2 A3 B1 B2 B3 B4 B A A1 A2 B1 B2 B3 B A
M:N relationship Mandatory relationship on both sides: Optional relationship on both sides: A1 A2 A3 B1 B2 B3 B A B A A1 A2 B1 B2
Reading an ERD FacSSN FacSalary FacRank FacHireDate Faculty OfferNo OffLocation OffTime Offering OfficeNo OffPhone OffType Office Based on the ERD above, we can say that: An Office has zero or one Faculty working in it A member of Faculty works in one and only one Office A member of Faculty team teaches zero or many Offerings An Offering is taught by zero or many Faculty
Example Draw: An occurrence diagram An entity-relationship diagram for the following description: “A car may be driven by many drivers during the week, or by none. A driver may drive many cars, and always drives at least one”
Example Draw an ERD for the following description. Explain any assumptions you need to make where there is insufficient information. “A cricket team has several players, but a player plays on only one team. A team has one manager”
Many-to-many relationships M:N relationships are sometimes called non- specific relationships They can always be resolved into pairs of 1:N relationships, and this should be done during modelling, before the ERD is mapped to relational tables - because we can’t implement a M:N relationship directly as tables Resolving the relationship gives more precision to the model, and may reveal more attributes/ relationships than were previously apparent
Resolving an M:N relationship using an associative entity Create another entity to represent the combination of the participating entities: STUDENT OFFERING ENROLMENT STUDENT OFFERING This is known as an associative entity (also called an intersection or association entity) The identifier of the associative entity is the combination of the identifiers from the related entities