[Koha-zebra] CQL queries into MARC records (Was: .abs file and subfield ordering)

[Mike Taylor]

> Date: Tue, 14 Feb 2006 20:27:57 -0800
> From: Joshua Ferraro <address@hidden>
> 
> Also, speaking of mappings, I've got a few CQL questions. So I
> understand the notion of a 'context set' and 'indexes' within each
> context set. I'm not clear on what the best context set would be for
> the MARC records in the libraries using Koha. bath?  cql?

Hi, Josh.  The first thing to get clear is that when figuring out how
to do particular searches with CQL, the question is not what _context
set_ to us, but what profile -- and in general a profile will draw
indexes from multiple context sets.  This is analagous to the choice
you make when wanting to represent data in XML: you don't choose what
_namespace_ to use, but what schema to use -- and in general a schema
will draw elements from multiple namespaces.  (The correspondance
between CQL context sets and XML namespaces is so strong that I have
wondered whether we should rename the former as CQL namespaces.  What
do you think?)

With that cleared up, it's time to evade your question!  We'll be able
to give you more definitive answer after the the big SRU meeting in
The Hague at the start of March, but to summarise the state of play,
there are potentially four ways to do bibliographic searching with CQL
on the table(!)

One approach is to use the Bath profile at
        http://zing.z3950.org/srw/bath/2.0/
which as you'll notice draws indexes both from the DC context set and
from its own Bath context set.  Regarding this approach, you
compained:

> Also, though the bath context set defines indexes, it doesn't
> clearly specify mappings for those indexes into any specific record
> format like MARC.

That's deliberate: the Bath set is not searching MARC records
specifically, but bibliographic records in general.  The indexes are
defined in terms of their semantics (delegating these definitions to
the DC element set and the Bath Z39.50 Profile) rather than their
encoding in a particular record format.

For some applications, this is what you want; but for Koha, which can
be seen as an application for maintaining MARC records, it's probably
not.  Think of the Bath profile as primarily for facilitating
interoperability between diverse bibliographic searching
implementations, especially to make metasearching more comprehensible.

The second approach to bibliographic searching in CQL is to use the
forthcoming MODS profile.  That's yet to be nailed down, but as the
name suggests will be based on the MODS XML Schema, with mappings
between indexes and elements clearly specified.  It fills more or less
the same ecological niche as the Bath profile, and may even supersede
it.  Again, the idea is that the indexes are primarily defined
semantically (and the crosswalk to MODS elements is a bit of an
after-the-event helping hand) so it's probably not what you want.

The third approach is to use the forthcoming MARC profile, and I
suggest that this _is_ what you need, as it's tied to the MARC syntax
specifically.  The proposal has not yet been written up, but basically
searches will look like this:
        marc.245=dinosaur and marc.245$c=farlow
As you can see, it's very structural.

(The fourth approach is based on the OpenURL metadata formats for
books, articles, dissertations and patents; I think it's a pretty bad
idea, but even if it's accepted the intention will be that it's
pretty much exclusively for the use of OpenURL resolvers, so it's
really not directly relevant to what you want to do.)

Hope this is helpful; sorry if it's more detail than you wanted.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <address@hidden>  http://www.miketaylor.org.uk
)_v__/\  "There is hopeful symbolism in the fact that flags do not wave
         in a vacuum" -- Arthur C. Clarke, on the moon landings.