According to the SAP HANA Performance Guide for Developers1, the .hdinamespace file is a JSON resource that defines the naming rules for the run-time objects in a multi-target application. The name parameter specifies the common name-space prefix for the objects, while the subfolder parameter determines whether the name of the sub-folder is added or ignored in the run-time name space. If you want to keep the names of the objects as short as possible, you should set the subfolder parameter to ignore, so that the name of the sub-folder is not appended to the name-space prefix and the object name. For example, if you have a table named CUSTOMERS in a sub-folder named SALES, and you set the subfolder parameter to ignore, the run-time name of the table will be com.sap.hana.example::CUSTOMERS, where com.sap.hana.example is the name-space prefix defined by the name parameter. If you set the subfolder parameter to append, the run-time name of the table will be com.sap.hana.example.SALES::CUSTOMERS, which is longer and more complex. For more information on the .hdinamespace file and the naming rules, see [The HDI Name-Space Configuration File]2 and [Run-Time Name Spaces in SAP HDI]3.
References: 2: The HDI Name-Space Configuration File 3: Run-Time Name Spaces in SAP HDI 1: SAP HANA Performance Guide for Developers