Tutorial on E-R Diagrams. Learn basic terminology and symbols See next four slides; refer to as needed in steps 2-4 below Learn the basics of E-R diagramming using Rational software
ITEMTerminology and Symbols:Entities, Attributes, Relationship
Primary Key (attribute(s) that form(s) a unique identifier for an instance of an entity) is underlined.
from parent perspective
(Parent Role – verb phrase)
Cardinality = 1
Cardinality of relationship
Cardinality = 1..n
Description of relationship
from child perspective
(Child Role – verb phrase)
Terminology and Symbols:Cardinality (and Role in Rational)
Hint: Make the entity with the cardinality = 1 the parent, i.e., start drawing the relationship from that entity. In this example Invoice is the parent, Invoice Item is the child.
Hint: Role descriptions can be entered in “verb phrase” or “inverse verb phrase” in the Properties window in Rational.
ItemDraw This Diagram with Both Tools
Note: With the Hoffer template and stencil in Visio, use the diamond symbol to show a relationship between entities. Put the name of the relationship in that symbol. (The inverse name may be omitted.)
Note: This diagram will have a different appearance in Rational. Entities will appear as “tables” with the attributes being “columns” within the “table.” Examples of cardinality are 1 for mandatory and 0..* for optional many.