Re: deductive databases

From: Simon Taylor <stayl_at_cs.mu.oz.au>
Date: Tue, 17 May 2005 05:35:50 GMT
Message-ID: <428982b5$1_at_news.unimelb.edu.au>

In article <1116283418.903814.273940_at_f14g2000cwb.googlegroups.com>, Mikito Harakiri wrote:
>
> Jan Hidders wrote:

>> Mikito Harakiri wrote:
>> >
>> > Returning to OP question:
>> >
>> > "AFAIK the expressive power of modern state-of-art database

> software

>> > like Oracle and PostgreSQL still falls far behind first-order

> logic:

>> > it essentially doesn't have functors or recursion."
>> >
>> > In SQL DBMSs aren't "function symbols" just UDFs (aka stored
>> > procedures), then? Including fairly recent incarnations: table
>> > functions?
>>
>> 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. Without that, database developers have to resort to kludges like NULL or excessively complex relational decompositions to deal with missing or optional data.

Simon Taylor. Received on Tue May 17 2005 - 07:35:50 CEST