Re: deductive databases
Date: Tue, 17 May 2005 16:31:59 GMT
Message-ID: <30pie.93684$yc.5551208_at_phobos.telenet-ops.be>
Simon Taylor wrote:
> In article <1116283418.903814.273940_at_f14g2000cwb.googlegroups.com>, Mikito Harakiri wrote:
>>Jan Hidders wrote:
>>>
>>>The way that function symbols are interpreted in Prolog and what gives
>>>them their expressive power in combination with recursion is more like
>>>what you would call a tuple constructor. So a term like f(x,y)
>>>represents a binary tuple with fields x and y and a label f that
>>>distinguishes it from g(x,y). So a better analogue would be user-defined
>>>record types where the type system allows arbitrary deep nesting or
>>>recursive types.
>>
>>I'm not sure I see the significance of nesting, although I seem to get
>>a feeling why genericity of record type is a big deal.
> > Nesting is not significant; it's allowing data structures to express > choice that increases the expressive power.
I tend to disagree. Choice by itself can always be flattened, but arbitrary deep nesting cannot, so it does matter for the expressive power of the query language.
- Jan Hidders