This tutorial provides instructions on creating entity-relationship (E-R) diagrams using Rational software and Visio. It begins by explaining basic E-R diagramming terminology and symbols. Next, it guides you through creating a simple E-R diagram of an invoice-invoice item relationship in both tools to demonstrate their different interfaces. The tutorial concludes by defining identifying and non-identifying relationships.

1. Tutorial on E-R Diagrams
1.
Learn basic terminology and symbols
–
1.
Learn the basics of E-R diagramming using Rational software
–
–
1.
See next four slides; refer to as needed in steps 2-4 below
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Start – Programs – Local Applications – IBM Software Development
Platform – IBM Rational Software Architect – IBM Rational Software
Architect
Follow through the notes in the Word document
(Rational_Software_Architect_Data_Modeling.doc)
Learn the basics of E-R diagramming in Visio
See http://www.sba.uwm.edu/Nazareth_D/Tools/Visio/homeTemplate.html
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Or sbacrseMIS 380Fall 2007Hoffer - Additional Templates.htm
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Try drawing the diagram in 4 below.
1.
Draw a diagram
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Draw the diagram on the last slide using both tools

2. Terminology and Symbols:
Entities, Attributes, Relationship
Attributes
(Columns)
Invoice_Num
Invoice_Date
Vendor_ID
INVOICE
Paid?
Primary Key
(attribute(s) that
form(s) a unique
identifier for an
instance of an
entity) is
underlined.
Includes
Relationship
Is_included_on
Qty_Added
INVOICE
ITEM
Entities
(Tables)

3. 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.
Description of relationship
from parent perspective
(Parent Role – verb phrase)
INVOICE
Cardinality = 1
Includes
Cardinality of relationship
Cardinality = 1..n
Is_included_on
Hint: Role descriptions can be
entered in “verb phrase” or
“inverse verb phrase” in the
Properties window in Rational.
INVOICE
ITEM
Description of relationship
from child perspective
(Child Role – verb phrase)

4. Identifying Relationship
• An identifying or mandatory relationship defines an
association between tables (i.e., entities). The identifying
relationship establishes the mandatory link between a
child table and a parent table. An instance of the child
table cannot exist without an instance of the parent table.
• An example of a parent and child table mandatory
relationship is when your database maintains a table
with data containing information about customer orders
in one table called, Orders, and holds order line-item
information in another table called, Order_Details. An
instance of the child Order_Details cannot exist without
an instance of the parent Orders.

5. Non-Identifying Relationship
•
A non-identifying relationship specifies an association between two
tables (i.e., entities). An instance of each table has its own identity.
One type of non-identifying relationship is an optional relationship.
Another is mandatory.
• Use an optional non-identifying relationship when a parent instance
is not required. Employees may be assigned to work on projects,
and projects may have employees assigned to work on them, but
such assignments are optional. “Employee” and “Project” have a
non-identifying relationship.
• Use a mandatory non-identifying relationship when a parent
instance is required. If an employee must be assigned to a
department, and a department must have at least one employee
assigned to it, “Employee” and “Department” have a mandatory nonidentifying relationship.

6. Draw 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.)
Invoice
Includes
Invoice
Item
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.

7. Draw 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.)
Invoice
Includes
Invoice
Item
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.