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Yukon College COMP 210 - Fall 2003
Database Design I
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Crow's Foot Entity-Relationship Diagram Notation

There are many different ER diagram notations, and the textbook uses the most unweildy of these. However the style known as "crow's foot" (for the splayed lines at the end of some relationships) is in wide use. I prefer the crow's foot notation, but you are free to use the text's notation or UML if you prefer for your project design, quizzes, or on the final exam.

Please note that no diagraming notation can express all modelling situations perfectly, or even unambiguously. If there is every any question over the meaning a portion of the diagram, simply add a note explaining your intent.

The following diagram illustrates most of the crow's foot notational elements:

Crowfoot and UML Entity-Relationship Diagram Notation

From this diagram, we can say the following about the model's entities:

  • STUDENT is a strong entity with the attributes: student_number, name, and address. The student_number attribute is also an identifier.
  • DISTANCE_STUDENT is a strong entity with the attributes: community and local_tutor. This entity does not have an identifier.
  • COURSE is a strong entity with the attributes: course_number and title. The course_number attribute is also an identifier.
  • TRANSCRIPT is a weak entity with the attribute: grade. This entity does not have an identifier.

And the following about the model's relationships:

  • A STUDENT may enroll in zero, one, or many COURSEs. A COURSE may be attended by zero, one, or many STUDENTs. The date that a specific STUDENT enrolls in a specific COURSE is recorded in the registration_date attribute of this relationship.
  • A STUDENT either has been issued a single TRANSCRIPT or has not. A TRANSCRIPT is assigned to a single STUDENT.
  • A TRANSCRIPT must record the grade for at least one COURSE, but may record grades for many COURSEs. A COURSE may appear on zero, one, or many TRANSCRIPTs.
  • A COURSE may specify zero, one, or many prerequisite COURSEs. A COURSE may be a prerequisite for zero, one, or many COURSEs.
  • A DISTANCE_STUDENT is a subtype of STUDENT: it "inherits" all of the attributes of STUDENT together with its own attributes.
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