Creating entity relationship diagram

ERD, short for entity relationship diagram, is a kind of diagram for presenting the properties as well as the relationships between data or participants. Database designer use of ERD to model physical structure of a relationship database, while business analyst uses ERD to model the data that is logically required or produced by processes.

A sample ERD

Creating entity relationship diagram

To create an entity relationship diagram right click on Entity Relationship Diagram in Diagram Navigator and select New Entity Relationship Diagram from the popup menu.

Create an ERD  through Diagram Navigator

When a new diagram is created, you can name it at the top left corner of diagram. At the top right of diagram you can select a type of model of which the diagram will present. The meaning of model types will be described in the next section.

Selecting a type of model

Creating entity and adding columns

To create an entity, select Entity in diagram toolbar and click on diagram. To add a column in entity, right click on the entity and select New Column from the popup menu.

Conceptual, logical and physical model

Conceptual, logical and physical model are three different ways of modeling data in a domain. The all contain entities and relationships, but differs in complexity and purposes. A general understanding to the three models is that, business analyst use conceptual and logical model for modeling the data required and produced by system from a business angle, while database designer refine the early design to produce the physical model for presenting physical database structure ready for database construction.

Conceptual model is the simplest model among all. It consists of entities and relationships. You can add columns to entities to represent the properties of entities.

A conceptual model

Logical model is more complex than conceptual model. You can include more details for columns by specifying their type (e.g. text, integer, date).

A logical model

Physical model is the most complex one. Database designers add primary or foreign keys to entities, and rename entities and columns to satisfy the table or column naming convention. The physical model represents how to implement your data model in database.

A physical model

Creating partial table

Sometimes, you want to separate an entity into two, and create a one-to-one relationship in between. For example, to extract information on a Student entity into another entity StudentInfo. You can split a table by creating a partial table through the resource centric-interface.

1. To split a table, move the mouse pointer over the entity you want to split and drag out the One-to-One Relationship -> Partial Table.
   

   Create a partial table

2. Release the mouse button to create the split entity.
3. In the Split Table dialog box, select the columns you want to move to the split table and click >.
   

   Move columns to partial table

4. Click OK button. A split table is created.
   

   Split table is created