Lesson 1.6: Create and manage a model diagram

Create a model diagram of for the Hotel Reservation System and understand how to delete objects in the model diagram.

You have two subject area diagrams for the Hotel Reservation System Model. Now bring them together into one model diagram. The model definition Hotel Reservation System already exists, but you have not created a diagram to represent it.

1 In the Tutorial encyclopedia, select the Data Modeling tab in the Explorer.

2 From the File menu, select New Diagram. A dialog will open presenting you with a list of possible diagram types. Double-click Entity Relation.

3 In the New Diagram dialog, enter the name of the diagram to be created, Hotel Reservation System, and click OK. The Diagram-Entity Relation dialog opens.

4 For the Diagram Status property, toggle on Model.

5 For the Model property, click Choices. The Select and Drag dialog will open, presenting a list of models already created in this project encyclopedia. Drag Hotel Reservation System into the Model property box and close the Select and Drag dialog (by clicking the X in the top right corner). Select ANSI for the DBMS property.

6 Click OK to close the dialog. The diagram will be created and all entities and relationships from affiliated subject area diagrams will be automatically drawn on the model.

Note Sometimes a model diagram does not always automatically display objects you have recently drawn on one of the subject area diagrams related to it. Select Dictionary Refresh. All entities and relationships on all related subject area models will be added to the model.

•Everything on a subject area ERD is in the Model ERD with which that subject area is affiliated.

•Objects on the Model ERD are not necessarily on any subject area ERD – they might be only on the Model ERD.

•You can delete an object from a subject area ERD without deleting it from the model.

•If you delete an object from the model, it is simultaneously deleted from all affiliated subject area diagrams.

1 Open the ERD Hotel Check-in.

2 Select the entity Vehicle. From the Edit menu, select Delete.

3 The displayed message gives you the option of deleting the entity from this subject area or from the model. Click "subject area." Notice the entity is no longer on the Hotel Check-in diagram and the relationship owns has been deleted as well.

4 Right click white space in the diagram and click Choices.

5 Drag Vehicle onto the diagram. Notice that the relationship with Guest is automatically re-established.

Note There is no undo facility in System Architect: when an object is deleted from a model diagram, its attributes and all its dependent relationships are deleted as well. Any data elements or structures used in an entity, however, are not deleted.