At 11:45 AM 7/18/2006, Mike wrote:
> It does occur to me that what we are facing is a collective
> coming-to-grips with the question of
> queries-as-transformations and transformations-as-queries,
Queries extract a small part of the information available from some
resource. Transformations convert the representation of information into a
different form. It's quite possible, therefore, for a task to involve both
query and transformation.
Indeed. An extraction of a list of phone numbers might be a "pure"
query. A plain-vanilla reformatting of a Docbook page into HTML might
be a "pure" transformation, or close to it. But most tasks involve
something of both. Right in the middle might be the creation of a
table of contents into a set of XML documents as rendered in HTML.
Not only that, but to addle our brains further ... sometimes it's
rather difficult to distinguish between the information and its
representation. The representation of information is itself
information (which is why a well-designed, scalable information
processing architecture will probably introduce some kind of
layering). In that respect, a transformation is a translation of one
kind of information (say, Docbook tagging) into another (say, the
code that drives a renderer to display the same "information" as the
source markup in a form friendlier to the eye and the educated
brain). But translation is rarely a simple mapping; it usually
involves the removal of some information (say, the nesting becomes
implicit in the level of headers rather than explicit in the markup
of sections) while other information is added (relative font sizing
is introduced for the display of those headers) -- generally, one
hopes, according to consistent rules derived from the relevant
context, which (in principle, if not too much is thrown away) may
even enable the translation back again.
This may seem like idle philosophizing until one considers that this
is effectively what queries do too, only balanced somewhat
differently with respect to adding and throwing away.
A query is a transformation scoped to a "repository" and returning an
extract of it. A transformation is a query scoped to a "document" and
returning an elaboration of it.
Cheers,
Wendell
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