> I was looking for the SQL syntax, not API calls (similar to BEGIN/COMMIT
> in Oracle, SQL Server, MySQL, ...).

Transactions can be started/ended by both API and DSQL,
so you do *not* have to use API (unless the limitation is in your access components).

> Also, I ran into a problem when creating indexes.
> > CREATE INDEX myindex ON LOGS (Id, Timekey);

...

> unsuccessful metadata update
> STORE RDB$INDICES failed
> attempt to store duplicate value (visible to active transactions) in
> unique index "RDB$INDEX_5"

You can ask e.g. in ISQL what the index is:

SQL> SHOW INDEX RDB$INDEX_5;
RDB$INDEX_5 UNIQUE INDEX ON RDB$INDICES(RDB$INDEX_NAME)

Now you see the index name (i.e. myindex) already exists in your database.

Ivan
http://www.volny.cz/iprenosil/interbase/