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3.3. Modeling Your View Metadata
When you create View Metadata, you are not describing the nature of your physical data storage. Instead, you describe the way your enterprise uses the information in its day to day operations.
View Metadata derives its classes and attributes from other metadata. You can derive View Metadata from Source Metadata that describes the ultimate sources for the metadata or even from other View Metadata. However, when you model View Metadata, you create special views on your existing enterprise information systems that you can tailor to your business use or application expectations. This View Metadata offers many benefits:
- You can expose only the information relevant to an application. The application uses this View Metadata to resolve its queries to the ultimate physical data storage.
- You can add content to existing applications that require different views of the data by adding the View Metadata to the existing View Metadata that application uses. You save time and effort since you do not have to create new models nor modify your existing applications.
- Your applications do not need to refer to specific physical enterprise information systems, offering flexibility and interchangeability. As you change sources for information, you do not have to change your end applications.
- The View Metadata models document the various ways your enterprise uses the information and the different terminology that refers to that information. They do so in a central location.
Our example enterprise information sources, the address book database, and the vendor supplied comma-delimited text file, reside in two different native storage formats and therefore have two Source Metadata models. However, they can represent one business need: a pool of addresses for a mass mailing.
By creating a View Metadata model, we could accurately show that this single View Table, the AddressPool, contains information from the two enterprise information systems. The View Metadata model not only shows from where it gets the information, but also the SQL operations it performs to select its information from its source models.
This View Metadata can not only reflect and describe how your organization uses that information, but, if your enterprise uses the JBoss Data Virtualization Server, your applications can use the View Metadata to resolve queries.
To create this View Metadata, you create a view and define a transformation for that view, a special query that enables you to select information from the source (or even other view) metadata models.
