Quite a few functions are supported in Derby's proprietary "JDBC escape syntax":
http://db.apache.org/derby/docs/10.8/ref/rrefjdbc88908.html
Most of those functions can also be used without that syntax, e.g.
SELECT
{fn abs(FIELD)}, abs(FIELD) FROM TABLE
will return two times the same value.
This doesn't hold true for TIMESTAMPADD and TIMESTAMPDIFF, which are not available in the "regular" syntax according to:
http://db.apache.org/derby/docs/10.8/ref/rrefsqlj29026.html
It would probably be a lot simpler for most users, not to get used to the
{fn ...}syntax.