18_EntityRelationship2 2.pdf - CITS1402 Relational Database...

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CITS1402 Relational Database Management Systems Video 18 — Entity Relationship Diagrams II Gordon Royle Department of Mathematics & Statistics
What is an ERD? Ask ten database designers and you’ll get ten different answers. An ERD is a visual way of representing I The entities being represented in the database I The attributes of those entities I The relationships between those entities I Certain constraints on all of the above
ERDPlus conventions I Entities are represented by rectangles I Attributes are represented by dangling ellipses I Relationships are represented by diamonds (But remember that ultimately, an RDBMS only has tables .)
A university database The university needs to maintain a student grade database with the following properties: I Students have a name and a unique student number I Units have a name and a unique course code I Students enrol in units in a particular year and get a mark
Entity Sets Entity sets are the collections of objects about which the database must keep information. For example, the collection of students and the collection of units are each entity sets.

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