Day 2 - Basic Database Backbone How to Model a Database Using E/R Diagrams How an E/R Diagram Translates to a Real Database

How do I model a database? Why do I need to model a system? Gives a team a basis to design a system on. Design Issues Entity Designs and Relationships Domain/Range Constraints of the System Good Entity Relationship Design Entity/Relationship Model Used to model the relationships between different objects in the database. Parallel structure to an object-oriented approach of thinking. CSE 498 Day 2 - Basic Database Backbone

Day 2 - Basic Database Backbone E/R Diagram Parts Entities Attributes & Keys Relationships Entity Major objects in a database. Strong Entity: Records are uniquely identified by its attribute(s). Weak Entity: Records are uniquely identified by its relationship(s). Weak entities are shown with double borders around the entity block. Customers Customers CSE 498 Day 2 - Basic Database Backbone

Day 2 - Basic Database Backbone Attributes & Keys Attribute A piece of information that defines a part of the entity. Drawn as ovals that link off an entity. Example: LastName Customers FirstName CustID Age Address Key Attribute(s) that uniquely identify an entity. Drawn by underlining the attribute name in the E/R diagram. Example shown above. CSE 498 Day 2 - Basic Database Backbone

Day 2 - Basic Database Backbone Relationships Relationship Diagram definition of how entities relate to each other. Drawn as a line between two objects with a diamond defining the relationship. An arrow defines the direction of the relationship. Weak relationships are drawn as double lines. Three types of relationships… 1 to 1 (One To One) N to 1 (Many To One) N to M (Many To Many) Rented By Rented By Rented By CSE 498 Day 2 - Basic Database Backbone

Example Simple Movie DB Customers CustID LastName FirstName Address CatID CatName Age Category In Category MovieID Rented By Title Rentals CopyNum Movie Rented CheckOut Duration Cost CheckOutDate CSE 498 Day 2 - Basic Database Backbone

How does an E/R translate to a DB? All entities become tables. All attributes become columns in the tables. Relationships are tricky… One-To-One and Many-To-One relationships are handled by adding in the keys from the higher level table to the lower level table. Many-To-Many relationships are handled by creating a table that has the keys from both entities to define the different relations. CSE 498 Day 2 - Basic Database Backbone

Movie E/R Diagram Translated to a DB Customer CustID (integer) -- Key LastName (VarChar) FirstName (VarChar) Address (VarChar) Age (int) CheckOut CustID (integer) -- Key MovieID (integer) -- Key CheckOutDate (Date/Time) Duration (integer) Cost (Money) Category CatID (integer) -- Key CatName (VarChar) Rentals MovieID (integer) -- Key Title (VarChar) CopyNum (integer) CatID (integer) CSE 498 Day 2 - Basic Database Backbone