"missing expression"

[JDogg306]

SQL plus is telling me "ORA-00936: missing expression" when I execute this PL/SQL code:
update KingsDepartments
set Professors = Professors_T(
(select Ref(O) from KingsCS O where O.Name = 'Professor Adam'), (select Ref(O2) from KingsCS O2 where O2.Name = 'Professor Alan'))
where Name = 'Computer Science';

And an asterix is placed under the first select. KingsDepartments is a table of Department_T objects, which contain a field Professors_T. Professors_T is a table of oids of objects of the same type as KingsCS contains.
Any idea why I'm getting this error?

Thanks in advance.

 

[expostfacto]

it looks like it thinks you're trying to call a function called professors_t.

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[appi]

Hi,

I guess it could be the last where clause which has no function so that the ref will be missing

(select Ref(O) from KingsCS O where O.Name = 'Professor Adam'),
(select Ref(O2) from KingsCS O2 where O2.Name = 'Professor Alan'))
where Name = 'Computer Science';

should be used with AND instead of where ??

regards
Uwe