Marten Feldtmann wrote: >> Hannu Krosing wrote: >> > >> >but as E can be an INT in one subclass and TIMESTAMP or
VARBINARYin >> >other >> >> I don't think that should be allowed. It violates inheritance principles, >> since the
typesare not compatible. > > I see ... here's a person who has always programmed with typed >languages and now thinks,
thatthis is the right definition .... it's >much more out there in the world. Open your mind and think about the
>following:> > An attribute named "a" of "type" TIMESTAMP of an instance of a class >can be seen as a relation from
thisclass to the class TIMESTAMP and >this relation is named "a". > > And if you're on the way to relations you're not
faraway to see, >that a relation is of course not limited to show to one specific class >... but perhaps to all
subclassesalso ... and this is not a >violation.
However the example I was referring to talked of INT4, TIMESTAMP or VARBINARY.
These are not subclasses but totally unrelated. Suppose you had
parent (id char(2)) child1 (a int4) child2 (a timestamp)
and someone asks for
select sum(a) from parent*
since the types are incompatible, the answer would be nonsense.
--
Oliver Elphick Oliver.Elphick@lfix.co.uk
Isle of Wight http://www.lfix.co.uk/oliver PGP key from public servers; key
ID32B8FAA1 ======================================== "We are troubled on every side, yet not
distressed;we are perplexed, but not in despair; persecuted, but not forsaken; cast down, but not destroyed;
Alwaysbearing about in the body the dying of the Lord Jesus, that the life also of Jesus might be made
manifestin our body." II Corinthians 4:8-10
