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From: tim@ohday.sybase.com (Tim Wood)
Newsgroups: comp.databases
Subject: Re: Summary: Full Text Database Products
Keywords: full text storage retrieval
Message-ID: <8457@sybase.sybase.com>
Date: 20 Feb 90 21:02:34 GMT
References: <1990Jan30.204658.1822@comp.vuw.ac.nz> <1990Feb19.235547.8915@comp.vuw.ac.nz> <768@dgis.dtic.dla.mil>
Sender: news@Sybase.COM
Reply-To: tim@ohday.UUCP (Tim Wood)
Organization: Sybase, Inc.
Lines: 24

In article <768@dgis.dtic.dla.mil> jkrueger@dgis.dtic.dla.mil (Jon) writes:
>
>You can't define indexing on [arbitrarily long byte strings], however.  
>So the operation will execute in time linear to table size.
>
>There's nothing inherent in the relational model that prevents one from
>handling user-defined types as first-class objects.  But to date no
>commercial RDBMS has done so.

One can index BLOBs (basic large object--conceptual instances of 
a user-defined datatype) by maintaining an identifier column value
of a simple datatype for each row containing a BLOB.  The indexing 
on the simple datatype is bound to be faster and more reliable than
the one-off indexing code a user writes for his/her BLOB datatype.
Moreover, one can change the "ordering" of the BLOBs by changing 
the identifier values, whereas with directly-indexed BLOBs one would need
to change the type-specific indexing algorithm.  This amounts to changing 
part of the datatype (or object type) definition.  
-TW
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tim@sybase.com          {pacbell,pyramid,sun,{uunet,ucbvax}!mtxinu}!sybase!tim
		This message is solely my personal opinion.
		It is not a representation of Sybase, Inc.  OK.