Re: Abstract Data Types

In article <9bs8lc$glb$1_at_news.tpi.pl>, Kazimierz Subieta says...
>
>
>"Jan Hidders" <hidders_at_REMOVE.THIS.win.tue.nl> wrote
>news:9bs37s$p2v$1_at_news.tue.nl...
>> Robert Schiller wrote:
>> > In the article Thirty Years of Relational: Extending the Relational
>> > Model by C.J. Date, Date talks about ADTs. What does he mean by
>> > abstract data types in the context of the relational model?
>>
>> Anything that can be described in terms of the operations that are
>> allowed upon it and has some kind of user readable representation. This
>> includes things like numbers, dates and strings but also more complex
>> things like lists, stacks and ... <drum roll> ... relations.
>
>Hmmmmm...not exactly. Relations are not abstract data types up to
>the time when one would define a complete and exclusive set of
>operations acting on relations. Stacks - yes, they are abstract data
>types because can be fully served by four classical operations:
>push, pop, top and empty. Can we imagine this set of operations for
>relations?

Just out of curiosity, wouldnt:

Empty, Insert, Union, Intersection, Difference, Product, Join, Select and Project

surve as an ADT for relation?

[...]

/Lennart Received on Sat Apr 21 2001 - 21:31:25 CEST