* A. Combine InfoProviders using Join and Unions: This is what a Composite Provider allows you to do in SAP BW/4HANA. A Composite Provider is an InfoProvider that combines data from several analytic indexes or from other InfoProviders (by union or inner join or left outer join), and makes this data available for reporting and analysis. Storing the data in BW Accelerator or in an SAP HANA database also ensures faster access to data in the query12.
* C. Define new restricted key figures: This is what a Composite Provider allows you to do in SAP BW/4HANA. A Composite Provider can define new restricted key figures based on the existing key figures of the underlying InfoProviders. Restricted key figures are key figures that are restricted by one or more characteristics13.
* E. Integrate SAP HANA HDI calculation views: This is what a Composite Provider allows you to do in SAP BW/4HANA. A Composite Provider can integrate SAP HANA HDI calculation views as part of its data sources, using a virtual table or an external SAP HANA view. This can enable mixed modeling scenarios that leverage both SAP BW/4HANA and SAP HANA capabilities14.
Reference:
* 1 https://help.sap.com/doc/saphelp_scm700_ehp02/7.0.2/en-US/63/f3c416bcbf4730bb86e62ef8a54e17/content.htm
* 2 https://blogs.sap.com/2018/12/14/implementing-mixed-modeling-in-bw4hana-using-composite-provider/
* 3 https://help.sap.com/doc/saphelp_nw75/7.5.5/en-US/42/f93a83ae5546d3a7cfd7ff09e25a2b/content.htm
* 4 https://help.sap.com/doc/SAP_BW4HANA_CONTENT/06e872f914a44d77b6c692b0273ca400/20b4b01f5baf46af8fbd439c741adf00.html

C. Full Outer Join:
* Combines data from both sources, including unmatched rows from either side.
D. Referential Join:
* Optimized join that assumes data consistency between the sources for faster query performance.
E. Inner Join:
* Only combines rows with matching keys in both sources, commonly used for exact matches.
References:SAP BW/4HANA Composite Provider documentation (SAP Help Portal).