You are using an SAP HANA database or a SAP BW Accelerator.
You have already created one or more analytic indexes, either in APD or by publishing SAP HANA models in BW. More information: Creating TransientProviders on SAP HANASAP HANA Models
A CompositeProvider is an InfoProvider, which combines data from several analytic indexes or from other InfoProviders (by Join or Union), and makes this data available for reporting and analysis.
A CompositeProvider created in the Analysis Process Designer can only contain analytic indexes.