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CMSC 461 Spring '99
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Entity-Relationship Diagram
E-R diagrams can have the following components:
rectangles
Used to represent entity sets.
The name of the entity set is inside the rectangle.
If the rectangle has a single line, it is a strong entity set.
If the rectangle has double lines, it is a weak entity set.
ellipses
Used to represent attributes. The name of the attribute is inside the ellipse, and if it is the primary key, the name is underlined.
diamonds
Used to represent relationship sets.
If the diamond has a single line, the relationship only includes strong entity sets.
If the diamond has double lines, the relationship includes a weak entity set.
lines
Used to link attributes to entity sets
Used to link entity sets to relationship sets
directed lines are used to show one-to-one or many-to-one relationships.
undirected lines are used to show many-to-many or one-to-many relationships.
label lines are used to show roles.
double ellipses
Used to represent multivalued attributes.
dashed ellipses
Used to represent derived attributes.
double lines
Used to represent total participation of an entity in a relationship set.
half diamond
Used to represent specialization/generalization.
box
Used to represent aggregates.
CSEE
|
461
|
461 S'99
|
lectures
|
news
|
help
Tuesday, 08-Jun-1999 11:59:42 EDT