Hi,
the Uby API as a standalone tool is just a means to query a UBY database.
In order to perform a text processing task such as semantic role labeling, the Uby API has to be queried from within a text processing framework, such as the UIMA-based DKPro Core component collection for natural language processing, see
https://code.google.com/p/dkpro-core-asl/.
There is a lot of background and information on UIMA-based text processing with Uby and DKPro Core, including sample code, in the recent UBY tutorial (May 2015), see the link here:
https://code.google.com/p/uby/While there are no code specific examples covering the the annotation of semantic roles, you might get an idea how this could be done.
Mind, however, that this would be a knowledge-based annotation which is not as robust as statistical semantic role labeling systems.
Best
Judith