Metadata Models

In Sybase Data Federation, a metadata model expresses a schema. Each metadata model defines a set of tables; each table contains a set of named columns and each column is associated with a data type.

Metadata models serve several purposes:

Validation: When you map a table in a metadata model to a data service, database operation, or database table, WorkSpace Data Federation informs you if the schemas of the metadata model table and the mapped object don’t match.
Aliasing: A table in a metadata model can be mapped (aliased) to a Data Federation object, such as a data service or a database operation, or to a table in a database. When the metadata model is deployed, the mapping lets you call each mapped object by the name of the corresponding table in the metadata model. (However, tables in metadata models have no relationships to one another.)
Deriving a view model schema: You can derive the schema for a new view model from a metadata model, which ensures that the results of any data service deployed from the view model conform to the metadata model.

Metadata modeling in Data Federation has important benefits:

Aliasing gives you easier access to mapped objects like data services.
When you map a metadata model to a Data Federation object, you can access the object using the metadata model’s name, which may be the same as the name of the database table from which it was created. For example, suppose you have a Crystal Reports application that accesses a table called Human-Resources.Employee in a relational database. You are building a data service, emp.DS, that selects and transforms data from the Human-Resources.Employee table, and you would like to make it simple to point the CR application at either the real database or the Data Federation data service for its data.

Solution: Import the schema for Human-Resources.Employee into WorkSpace Data Federation as a metadata model. You now have a model called HumanResources, which contains a table called Employee. Next, map the Employee table in the HumanResources metadata model to your emp.DS data service. This mapping lets you access the emp.DS data service as Human-Resources.Employee—the same name you use to access the table in the database. You can point your application either at the database or at Data Federation; no further changes are required.
You can ensure that data services you create conform to a particular schema.
Suppose you've created a schema in a modeling tool, such as Sybase PowerDesigner or ERwin, and you want to create a data service that produces results matching your schema.

Solution: Import the schema into WorkSpace Data Federation as a metadata model and derive a new view model from the metadata model. As you add operators to the view model, WorkSpace Data Federation monitors the schema and alerts you if the view model’s schema diverges from that of the metadata model. Any data services you deploy from this view model will match the schema you imported from the modeling tool.

CAUTION:

A derived view model’s schema is a snapshot of the parent metadata model’s schema. There’s no link between the view model and the metadata model, so if the metadata model changes, the derived view model’s schema will not be updated automatically—you must derive a new view model to capture the changes.