Create a Database Model (also known as Entity Relationship diagram) in Visio

There are two stencils that come with the Database Model Diagram template. As you begin to refine the structure of your diagram, work from the stencil that's right for you:

• Use the Entity Relationship stencil to model databases that are based on the SQL92 and earlier standards.

• Use the Object Relational stencil, which has additional shapes for working with types, to model databases that are based on SQL99 and later standards.

Use the Entity shape to create a table in your diagram:

1. From either the Entity Relationship or Object Relational stencil, drag an Entity shape onto the drawing.

2. Double-click the shape to open the Database Properties window.

3. Under Categories, click Definition and type a name for the table.

4. Under Categories, click Columns, type a name, and choose a data type.

5. Select the Req'd check box for columns that can't have null values.

6. Select the PK (primary key) check box for columns that uniquely identify each row in the database table.

7. Under Categories, click Indexes, Triggers, Check, or Extended to create these optional elements.

Use the Database Properties window to add or change properties for columns, including data types and primary keys:

1. Double-click the table in your diagram.

2. In the Database Properties window, under Categories, click Columns.

3. Click in the first empty Physical Name cell, and type a name.

4. To change the data type for a column, click the column's Data Type field, and then select a data type from the list or type it into the list. For example, you can type decimal(8,2) or char(30).

5. To prevent null values, select the Req'd check box.

6. To specify that the column is a primary key, select the PK check box.

7. To see more column properties in addition to those that appear when you click the Columns category, select the column and then click Edit.

Relationships use primary and foreign keys to allow databases to match a row in one table with a row in a related table. You can show those relationships in your diagram. In addition, you can set their cardinality (for example, one-to-many) and use either Crow's feet, Relational, or IDEF1X notation to show the cardinality. You can't show many-to-many relationships with any of these notations in the Database Model Diagram template.

Create a relationship between tables:

1. Make sure that both tables are visible in the diagram. If you reverse engineered the model from an existing database, you may need to drag one or both from the Tables and Views window onto the drawing page.

2. Double-click the table that you want for the primary key side of the relationship.

3. In the Database Properties window, under Categories, click Columns.

4. In the grid, click the column that you want to use to uniquely identify each row in the table, and select the PK check box to set it as the primary key.

5. From the Object Relational or Entity Relationship stencil, drag a Relationship shape and drop it onto a blank space on the page.

6. Connect the higher end to the table with the parent table.

7. Connect the other end to the child table.

   If the second table doesn't already contain a column with the same name as the primary key, the modeler adds it to the second table as a foreign key.

   Note: If relationship lines disappear, on the Database tab, in the Manage group, click Display Options. On the Relationships tab, under Show, select the Relationships check box.

Set the relationship's cardinality:

1. Double-click the relationship.

2. In the Database Properties window, under Categories, click Miscellaneous.

3. Under Cardinality, choose the cardinality that best fits the relationship. For one-to-many relationships, the best choice is either Zero or more or One or more. For one-to-one relationships, the best choice is either Zero or one or Exactly one.

Indexes improve the performance, or speed, of your database when you run a query.

1. Open the database model diagram.

2. Double-click the table to which you want to add an index, and in the Database Properties window, in the Categories list, click Indexes.

3. Click New.

4. In the Create Index dialog box, type a name for the index, and then click OK.

5. In the Index Type list, select an option to create a unique or non-unique index.

6. In the Available Columns list, select the name of each column that you want to include in this index, and then click Add >.

7. In the Indexed Columns list, select the Asc check box to create an index that has an ascending sort order, or clear the check box to create an index that has a descending sort order.

   The database model diagram is updated.

You can think of a view as a saved query. Views are particularly handy if you need to repeatedly access the same information from multiple tables, or if you want to expose the data to users without letting them change the actual tables.

From the Entity Relationship or Object Relational stencil, drag a View shape onto the drawing page.

Depending on your database management system (DBMS), you may be able to set extended properties for tables or views to determine where they are stored.

Double-click the table or view whose extended properties you want to set, and in the Database Properties window, in the Categories list, click Extended.

Use check clauses to ensure that the data that is entered into a column is within a particular range of values. For example, you can create a check clause that requires the data in a column called "Age" to be over 65.

1. Double-click the table to open the Database Properties window.

2. Under Categories, click Columns and then click the column that you want to add a check clause to.

3. Click Edit.

4. On the Check tab of the Column Properties dialog box, enter the constraints that you want. For more information about your choices, see Column and Field Properties dialog box (Check tab).

   The check clause is added to the Code window under Local code.

Use stored procedures and user-defined functions to create packets of code that you can reuse to perform the same actions repeatedly. The major difference between the two is that a user-defined function returns a value, whereas the stored procedure executes code without returning a value.

1. On the Database tab, in the Show/Hide group, select the Code check box to open the Code window.

2. Click Global Code and then click New.

3. On the Properties tab of the Code Editor, click the kind of code that you want to create, and type a name for the code.

4. On the Body tab, type the code and then click OK.

Triggers cause SQL code that you specify in the trigger to run when a particular event occurs in the database.

1. Double-click the table to open the Database Properties window.

2. Under Categories, click Triggers, and then click Add.

3. On the Properties tab, type a name for the trigger.

4. On the Body tab, type the code and then click OK.

   The trigger is added to the Code window under Local code.