Tutorial on E-R Diagrams

1. 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 • 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 • Or sbacrse\MIS 380\Fall 2007\Hoffer - Additional Templates.htm • Try drawing the diagram in 4 below. • Draw a diagram • Draw the diagram on the last slide using both tools

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

3. Description of relationship from parent perspective (Parent Role – verb phrase) Includes Cardinality = 1 INVOICE Cardinality of relationship Cardinality = 1..n Is_included_on Description of relationship from child perspective (Child Role – verb phrase) INVOICE ITEM 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.

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 non-identifying relationship.

6. Invoice Includes Invoice Item 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.) 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.