For ADS/Online, all CA-supplied Built-In Functions (BIF) modules are linked with ADSOMAIN and all user written BIF modules (USERBIF1/2/3/4/5) can optionally be linked together into a new ADSOVCON module.
IDMS - all supported releases
In releases prior to 18.0, user written built-in functions had to be linked with ADSOMAIN for ADS/Online and ADSOBAT2 for ADS/Batch to improve performance.
Since IDMS 18.0 this is no longer necessary. The user built-in functions can be linked together into an ADSOVCON load module using #BIFVCON macros. This module is used by both ADS/Online and ADS/Batch.
Note that all CA-supplied BIFs are still linked together with ADSOMAIN/ADSOBAT2.
ADS Reference Guide in the section Linking Built-In Functions With The Runtime System.