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Drawing 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.
Creating entity relationship diagram
Right click on Entity Relationship Diagram from Diagram Navigator and select New Entity Relationship Diagram from the pop-up menu.
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| Create entity relationship diagram |
Enter the name for the diagram. At the same time, a Data Model selection box appears on the top right corner of the diagram.
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| Select data model |
All model elements created on diagram will follow this Data Model setting. Only Physical Model will be able to generate SQL. Leave it as default (Physical Model).
Drawing entity
Click Entity from diagram toolbar and drag it on the diagram pane.
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| Create entity |
Click on diagram and specify the entity name.
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| Rename an entity |
Right click on the entity and select New Column from the pop-up menu, or press Alt+Shift+C.
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| Create column |
The column can be set with primary key by right clicking the column and selecting Include in primary key from the pop-up menu.
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| Set as primary key |
Drawing relationships
Point on the entity and either click or drag its resource icon to create another entity.
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| Create relationship |
As a result, a new entity is created with foreign key column(s), referencing the original entity's primary key column(s).
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| Rename relationship |
Drawing many-to-many relationship
Click or drag Many-to-Many relationship resource icon of an entity.
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| Create many-to-many relationship |
Many-to-Many relationship will auto convert to two One-to-Many relationships and a join table. The primary key both tables will be used to create foreign key columns in join table as composite primary key.
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| Created join table with one-to-many relationships |
Defining default schema
A default schema can be set on diagram, to make entities to be created on the diagram share the same schema. To define a default schema on diagram:
Right click on the diagram background and select Open Specification... from the pop-up menu.
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| Select Open Specification... from the pop-up menu |
Specify the default schema in the Entity Relationship Diagram Specification dialog box. Click OK to confirm the change.
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| Specify default schema |
Now, when you create an entity on the diagram, the entity will be under the default schema.
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| An entity with myschema as its schema |
| NOTE: | In order to move entities in a diagram to a schema, define default schema on the owning entity relationship diagram, right click on the diagram and select Apply Default Schema from the pop-up menu. This will make all entities that have master view on the erd to share the schema defined. |
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.
- 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.
To create a partial table - Release the mouse button to create the split entity.
- In the Split Table dialog box, select the columns you want to move to the split table and click >.
Move columns to partial table - Click OK. A split table is created.
Split table is created
| Chapter 1. Database Modeling | Table of Contents | 2. Drawing sequence |