1. Technical Module A Data Modeling Definitions
Entity-relationship diagram (ERD) -- a diagram that shows the entity types of an organization, and their relationships.
Entity type -- something of value to the firm, described with data, occurs multiple times.
An environmental element of the firm (Customer)
A resource (Product)
An important transaction(Customer invoice)
Entity – an occurrence of an entity type (ABC Co., Widget, Invoice 123)

2. Definitions
Relationships – how one entity type is related to one or more other types
Fig A.1: Examples of Entity Types and Relationships

3. Definitions
Cardinality – the number of times one entity type can exist in the relationship
Fig A.2: Examples of Cardinalities

4. Definitions Optional and mandatory relationships
Fig A.3: Examples of Optional Relationships

5. Definitions Attributes Identifier (Employee number)
Descriptor (Employee name)
Fig A.5: Entities with Attributes

6. Development of an ERD Steps Identify entity types.
Identify the relationships.
Prepare a rough ERD.
Map attributes to entity types.
Perform a data analysis.
Prepare a modified ERD.
Review with others and refine.

7. Development of an ERD
Prepare rough ERD.
Fig A.6: A Rough ERD

8. Development of an ERD
Map attributes to entity types.
Table A.1

9. Development of an ERD Perform a data analysis (normalization)
First normal form (occurs n times?)
Sales order body lines occur n times.
Fig A.7: A Sales Order Form

10. Normalization Establish each body line as an entity type.
Fig A.8: Added Entity Types to Eliminate many-to-Many Relationships

11. Normalization New entity types have composite keys.
Table A.2: Additional Entity Type Attributes

12. Normalization
Second normal form (entire composite key needed for identification?)
Table A.3: Additional Entity Type Attributes in Second Normal Form

13. Normalization
Third normal form (descriptor elements dependent on other descriptor elements for assignment of values?)
Table A.4: Normalized Entity Type Attributes

14. Development of an ERD
Prepare modified ERD.
Fig A.9: A Modified ERD

15. Relational Databases Implicit relationships
Fig A.10: An Example of Implicit Relationships

16. Relational Databases Example of implicit relationships
Fig A.11: An ERD of Purchasing Data with Selected Attributes

17. Data Dictionary A data dictionary entry
Fig A.12: A Portion of a Data Dictionary