Re: Object-relational impedence
Date: Sun, 09 Mar 2008 11:25:42 +0000
Message-ID: <fr0hft$8gf$1_at_aioe.org>
> S Perryman <q_at_q.com> wrote in news:fqpj0o$lke$1_at_aioe.org:
TN>In the other message TN>you dismissed projection as being covered by the concept of TN>subclassing.
SP>No. Projection is covered by *type substitutability* .
TN>Can you please be more specific? If we remove some [data] TN>attributes, does it mean the resulting "entity" is a subclass.
>>No, merely that the resulting entity is now deemed to be of
>>another type, substitutable with the original type.
>>type T
>>{
>> x, y, z
>>}
>>
>>Set<T> ts ;
>>Set< type { x, y } > ps = { e IN ts : e.x > 123 } ;
>>The elements of ps are effectively projections of the elements in ts.
> Hold on, you have a value of type Set<T> assigned to a variable of type > Set<type{x,y}>.
So the assignment is a projection is of a type (x,y,z) to a type (x,y) .
Regards,
Steven Perryman
Received on Sun Mar 09 2008 - 12:25:42 CET