Tutorial. Creating ERDs Using

Transcription

1 Tutorial Creating ERDs Using Microsoft Visio 2007 Sandra Dyke, 2009 Visio 2007 Tutorial: Creating ERDs

2 Contents Page Using Visio to Create ERDs... 1 Let s Get Started... 3 Changing the Relationship to Show Crows Feet... 3 Adding Attributes... 5 Adding Relationships... 6 Describing the Diagram... 7 Changing the Default Relationship Created by Visio... 8 Sandra Dyke, 2009 Visio 2007 Tutorial: Creating ERDs

3 Using Visio to Create ERDs This brief tutorial will demonstrate how to use Visio to construct an ERD for a basic sales system. It is the same example used in the Microsoft Access 2007 tutorial. In this tutorial an ERD with 4 tables will be created with the following tables and attributes with the stated data types and sizes: Entity Attribute Data Type Size Required Customer CustomerID AutoNumber Y CustomerFirstName Text 50 Y CustomerLastName Text 50 Y CustomerAddress Text 50 Y CustomerSuburb Text 50 N CustomerCity Text 50 Y CustomerPostCode Text 4 N CustomerPhoneNumber Text 15 N Inventory InventoryID AutoNumber Y InventoryName Text 50 Y InventoryDescription Text 255 N Employee EmployeeID AutoNumber Y EmployeeFirstName Text 50 Y EmployeeLastName Text 50 Y EmployeeExtension Text 4 N Sale SaleID AutoNumber Y CustomerID Number LongInteger Y InventoryID Number LongInteger Y EmployeeID Number LongInteger Y SaleDate DateTime Y SaleQuantity Number Integer Y UnitSalePrice Currency Y Notice that the names of each attribute are typed with no spaces between the words, but each new word starts with a capital. This is called CamelCase. Don t use spaces in field names because different database programmes treat these differently and it can also cause problems with creating queries later. Also notice that each attribute name has the table name in front of it. This is not always done, but is useful when the same field name may be used for different tables. For example, this database also has an Employee table where the employee name is included. By including the table name in front of the field name, it is easier to determine which field is being referred to when using queries and reports. Sandra Dyke, 2009 Page 1 Visio 2007 Tutorial

4 Relationship diagram created in the Microsoft Access 2007 Tutorial Sandra Dyke, 2009 Page 2 Visio 2007 Tutorial

5 Let s Get Started Open Visio and select Database Model Diagram from the Database Option The only items we are using are Entity and Relationship Changing the Relationship to Show Crows Feet Go to Database Options Document Change the Database Documents Options to show the following: Sandra Dyke, 2009 Page 3 Visio 2007 Tutorial

6 To use these items, click on them and drag (still holding down the left mouse button) them onto the drawing canvas. Don t worry about their size because Visio controls this and the size is related to what is typed into them. Drag an Entity onto the drawing canvas Click on the Entity This opens the database properties dialogue box and allows the entity details to be included. Select the Definitions category and type Programme as the Physical Name Sandra Dyke, 2009 Page 4 Visio 2007 Tutorial

7 Adding Attributes Click on the Columns category Type the attribute names, change the data type if you want to, select the Req d and PK options as needed. By selecting PK, the attribute is moved above the line, underlined and has PK added to it. By selecting the Req d option, the attribute is made bold and indicates that this is a mandatory attribute. In this instance, CustomerSuburb is optional. If the order of the attributes needs to be changed, the Move Up and Move Down buttons can be used. Using the table at the start of the tutorial, add the rest of the entities and attributes. Don t worry about identifying the foreign keys at this stage, just add the attributes. Sandra Dyke, 2009 Page 5 Visio 2007 Tutorial

8 Adding Relationships Drag the relationship line over one of the tables until the table is outlined in red. Move the other end of the line over the other table until that table is outlined in red. This allows the line to snap onto the tables (shown by the large red box on the ends of the lines) and means when the tables are moved, the relationship line moves with them. Notice that the CustomerID in the Sale Entity is now labelled FK1. Because the attribute to make the primary key/foreign key relationship was already in the table, Visio automatically made it the foreign key. If the relationship line is an arrow rather than Crows Feet change the relationship type to Crows Feet (refer to Changing the Relationship to Show Crows Feet section above). To change the name of the relationship, click on the line and then type the relationship name in the verb phrase box in the Database Properties box: Sandra Dyke, 2009 Page 6 Visio 2007 Tutorial

9 Create and name the rest of the relationships. BE CAREFUL when deleting relationships Visio will delete the FK attribute as well!!! If the attribute is added by Visio as a FK, it will not be required so check that the attributes are all correctly shown when the diagram is finished. Compare this diagram with the relationship diagram produced by Microsoft Access on page 2. Describing the Diagram The relationships shown on the ERD are: A customer may create many sales A sale must be created by one customer An inventory item may be contained in many sales A sale must contain only one inventory item An employee may make many sales A sale must be made by one employee (Remember, this is a simple system a sale may include many items, but the business rule in this example is that a sale must only contain one item.) Sandra Dyke, 2009 Page 7 Visio 2007 Tutorial

10 Changing the Default Relationship Created by Visio Sometimes the relationship created by Visio is not correct. To change the cardinality and optionality shown, select the relationship and then go to the Miscellaneous category in the Database Properties box. Select the required option in the cardinality list. If it is still not correct, try changing the Relationship type. This may change the dotted line to a solid line. Once the cardinality is showing correctly, try changing the relationship type back again. If this changes the cardinality, leave the line as a solid line. Sandra Dyke, 2009 Page 8 Visio 2007 Tutorial