ERD Data Model

Draw an ERD for an eyeglass store database with the following information:
a. Customers have prescriptions from eye doctors.
b. Customers buy frames that come from manufacturers
c. Customers are helped by a staff member

Your Entity Relationship Diagram (ERD) posted for this discussion is NOT to be submitted as an attachment that everyone would have to open to read. Your ERD is to be copied and pasted.

You are to draw one ERD that includes all of the above relationships. Do NOT show the attributes for each entity.  Make sure that your relationships shows the cardinality for both directions (active and passive).  Use Crows Foot Notation. Name the relationships. There should be a minimum and maximum cardinality for each direction of each relationship.

Below are some guidelines you should use when drawing ERDs

An Entity Relationship Diagram (ERD) is a data model while Data Flow Diagrams (DFDs) are process models.

When drawing an ERD:

  • Each entity is to be named with a noun
  • The ERD shows the relationships between the entities.  The relationship is to be a verb.
  • Each entity has attributes (fields).  Attributes are the columns in regard to relational databases.  For the ERD you will draw in Discussion No 7 do not include the fields/attributes.

The ERD below states:

  • Reading the ERD in the active voice (top to bottom) – Person walks Dogs. Reading the ERD in the passive voice (bottom to top )- it states that dogs are walked by people.
  • Note the cardinality symbols.  They are in Crows Foot Notation, which is what we will use in this class – Discussion No 7 ERD.
  • The ERD states (reading top to bottom) PEOPLE walk one and only one dog (active).  Reading bottom to top (passive) – Dogs are walked by zero to many people.