First steps - Simple Derived Views

Now you are ready to explore the capabilities of the Denodo Platform that make Data Virtualization a very powerful tool. In the previous sections, you have connected to the CRM database and queried its tables. Client, client_type and address data is now available within Denodo, so you can start to build a unified view of a customer that will contain the information of the three tables and remove the need for each consumer of the data to create this unified view.

We create this unified view within the virtualization platform so it can be reused by all clients. Having it defined in a single point will make it easier to manage changes to our definition of the customers (For example, if, in the future, we only want to expose residential customers to the consuming applications or the source database is changed.) With Denodo, you will maintain the proper data definition and your final applications won't require any changes.

The way of creating this unified view of a customer is through a JOIN operation, just like it's done in a traditional relational database.

Join operation

Let's see an example of a derived view creation process using the join Operation. Before we begin, let's create a new folder named 3 - Derived Views to stay organized. Then, right-click in the elements tree and select New > Join. Now, an empty Join View panel will be shown in the Administration Tool workspace.

To select the views on which the join operation is going to be executed, you have to drag & drop them from the list of views that appear on the Elements Tree. As input views are added, the schema of the resulting join view is generated automatically.

In our example, you have to follow these steps:

1. Drag & drop the client, client_type and address views into the workspace.
2. Drag the client.client_id field and connect the arrow to the address.client_fid field to set one of the join conditions.
3. Drag the client.client_type field and drop the arrow on the client_type.code field.
   
4. Then, go to the Output tab. Here you will see both address and client views are producing the same field with different names: client_id and client_fid. You have to remove one of them selecting the field and clicking on "Remove selected" button.
   
5. Rename the view "personal_data_crm" by typing in the input box labeled "View name" at the top.
   
6. Click on the button to save the view.
7. Drag & drop the new element into our new 3 - Derived Views folder.

The Administration Tool will show the schema of the new derived view:

Once these steps are completed, you will have a derived view (virtual, data is not stored in Denodo) that represents the concept of a customer within your organization. This view can be queried in the same way that you did for the base views (check how to in the previous section). Now that this data is defined, your client applications can just retrieve this information directly from the virtualization server without having to define the data combination themselves.

The Denodo Administration Tool also provides a full set of relational operations, in addition to the join, to create new views:

• UNION
• PROJECTION
• SELECTION
• AGGREGATION
• MINUS/INTERSECTION
• FLATTEN

These operations can be used in the same way than the Join operation (Right-click > New > OPERATION), you can try yourself!