View Models

A Data Federation view model is the abstract, graphical representation of the processing performed for a particular integration task. A view model can be deployed as one or more data services.

The view model represents the flow of data from one or more input sources through a number of operators to an output result. From a view model, you can deploy one more data services, which perform the processing. You create a view model and deploy the resulting data service(s) using WorkSpace Data Federation.

The inputs to a view model can be relational result sets produced by database operations or data services; XML results produced by data services; data catalog files in CSV or XML format; HTTP operations; and web services calls.

A view model is not required to have any inputs; it can generate its own data. Nor is it required to have any operators—though there would be no point to a view model that has neither inputs nor operators.

View model outputs are also in result set format. Most operators produce a single output. (The exception is the Splitter operator.) Every view model includes a Result element, but a view model need not produce output. View models can produce at most one output result set.

Thus, a view model consists of:

• Zero or more input sources
• Zero or more operators to manipulate the data
• Exactly one Result element

• When to Use View Models
  There are two ways to set up a Data Federation data service: by creating a view model in WorkSpace or by writing your own data service plug-in.
• Schemas
  In a view model, each operator’s result set, from the inputs to the result, is defined by a schema consisting of an ordered set of typed columns. The output schema of the view model is the schema of the operator that is directly connected to the Result element.
• Operators in View Models
  WorkSpace Data Federation provides a selection of elements and operators you can use to manipulate data in a view model.
• Expressions in Operators
  Many view model operators allow or require you to enter JavaScript expressions that are evaluated at runtime to configure how your view model behaves.
• Parameters and Control Variables
  View models can have variables, which can be used by the various operators in the model. Variables include global parameters (that is, parameters to the entire view model or data service) and control variables introduced by some operators (such as Iterator and Custom).

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