data access should be done by using a set of SQL views that are intended to be "public" - so maintained and stable across product versions. These SQL views are known as "public views" and you can find the doc here: Accessing data using public views - BMC TrueSight Capacity Optimization 11.0. Here you can find also some useful examples: Query examples - BMC TrueSight Capacity Optimization 11.0.
Public views are the way the product exposes the main DB schema tables for creating custom data marts.
Using instead any "internal" tables or functions like SERIES_MODULE.GET_IND_NUM_VALUE is not officially recommended because there is no guarantee they will be maintained in future: they could be changed or dropped, so your queries could potentially break.
Said that, the two functions SERIES_MODULE.GET_IND_NUM_VALUE and ENT_CONF_MODULE.GET_STR_VALUE are quite stable so you could use them but, again, they are not part of the public API, so they are not documented and not supported. Maybe you could open an Idea on this community to include them in the public area.
Hope it helps,