Rubin: "Yes, in the context of this I think that I meant the APIs were copyrighted."

"By Sun?" Boies pressed.

"Yes," replied Rubin.

The Android chief was questioned for only 25 minutes, since he was called to the stand shortly before the trial ended for the day. Oracle will resume his questioning Tuesday, when Eric Schmidt, Google's executive chairman, is also expected to testify.

Earlier Monday, Oracle called Bob Lee, a former Google engineer who is now the CTO of mobile payments company Square, and John Mitchell, a computer science professor at Stanford University who Oracle hired as an expert witness in the case.