Data Source Output Parameters are set using the results from a data source and enable data source chaining.
Data Source Output Parameters are parameters whose values are set dynamically by a data source using values from a specified field in its result entries. Most often, these parameters are then used to filter subsequent data sources, a technique known as data source chaining.
Data source output parameters can be created in the data source editor. After a Source has been chosen, select a field in the “Parameter Output” dropdown. Once the data source is saved, it will add the output parameter to the parameter pool whenever it is executed.
For details on how to use a data source output parameter to filter another data source, see Data Source Chaining.
It's important to understand how Symphony's various field types work in order to use data source ouput parameters effectively. Some fields will use their handles to populate output parameters, while others, like Select Box Link, will use the IDs of the entries to which they're linked.