FDO uses filters through its commands (including provider-specific commands) to select certain features and exclude others.
A filter is a construct that an application specifies to an FDO provider to identify a subset of objects of an FDO data store. For example, a filter may be used to identify all Road type features that have 2 lanes and that are within 200 metres of a particular location. Many FDO commands use filter parameters to specify the objects to which the command applies. For example, a select command takes a filter to identify the objects that the application wants to retrieve or a delete command takes a filter to identify the objects that the application wants to delete from the data store.
When a command executes, the filter is evaluated for each feature instance and that instance is included in the scope of the command only if the filter evaluates to True. Filters may be specified either as text or as an expression tree. Feature providers declare their level of support for filters through the filter capabilities metadata. Query builders should configure themselves based on the filter capabilities metadata in order to provide users with a robust user interface. For more information, see What Is an Expression?.