As Daniel points out, XML, with its insistence on systems identifiers, is
not particularly friendly to the notion of the SGML open catalog in
particular or in general to the the concept of identifying external
resources as general entities.

As a result we at tyhe minnesota Hsitorical Society are using the HREF
attirbute rather than ENTITYREF in EAD linking elements.   This leaves one
with the problem of file location persistence on the Web unless you use purl
or file handler mechanisms.
In our case, this has not yet been a major problem as most of our links are
internal.  Things like our logo and navigation piece are driven by the
stylesheet rather than embedded in the document itself.

An additional problem we face with external enitities and XML lies in the
fact that stylesheets currently appear to have no way of accessing the
contents of entity references and extracting system identifiers- short of
customized programming.

For example:  I can declare the following entity in the document prolog-

<ENTITY eadlogo SYSTEM "eadlogo.gif" NDATA gif>

In the document, I can encode (in XML mode):

<extptr entityref="eadlogo"/>

But it appears that I cannot transform that expression into the required
format of  HTML format object like

<img src="eadlogo.gif">

because a stylesheet cannot access the ENTITY reference to extract the full
system identifier.

I hope someone can suggest a solution within XSL that I haven't been able to
devise or shares a piece of JavaScript or Pperl that will accomplish this.

I don't see how creating and storing the file in SGML mode solves this
issue.  At some point the entity reference has to be transformed into a
system identifier when the file is "published."

One alternative is to use the href attribute instead-

<extptr href="eadlogo.gif"/>

and avoid external entities completely which, as I said, what we do.

File location persistence with the attendant maintenance problems will
continue to be a problem for all Web content creators, not just for
archivists using EAD.  Unfortunately (or perhaps fortunately) the solutions
will have to come from outside the archival community.

This whole issue is discussed, of course, in the forthcoming EAD Application

In response to Ed's second question, there is a description of how we
generate files at the SAA EAD Round Table Help pages.  in short, our SGML
files are transformed in XML with a macro script file written some time ago.
An alternative would be James Clark's SP processor.  See   Some of the new XML software is very nice though.

Michael Fox
Head of Processing
Minnesota Historical Society
345 Kellogg Blvd West
St. Paul MN 55102-1906
phone: 651-296-1014
fax:  651-296-9961
[log in to unmask]

> ----------
> From:         Daniel Pitti[SMTP:[log in to unmask]]
> Sent:         Monday, April 26, 1999 6:52 AM
> To:   Multiple recipients of list EAD
> Subject:      Re: was: HTML or ASCII
> Ed,
> Yes, you are right in assuming that XML does not support SGML Catalogs.
> There is a proposal for an XML version of the catalog, but nothing
> official
> that I have seen. This is one reason why I recommend using SGML for your
> maintenance/archival source, and XML for publishing. In this scenario, you
> can supply "href" attributes on XML linking elements using batch
> processing
> of SGML documents and catalogs.
> On a related note, URNs are (slowly) becoming a reality at long last, and
> this will have an impact on the maintenance and delivery of SGML, among
> other things.
> Daniel
> At 10:00 AM 4/24/99 -0400, you wrote:
> >Michael, I was interested to read:
> >
> >"In a phrase that I think Bill Landis coined, we are treating our finding
> >aids as data and not as text.   We have chosen to create and maintain our
> >files in xml mode."
> >
> >Am I right in saying that XML doesn't support something like SGML
> Catalogs,
> >which can allow you to maintain the file locations of external entities
> >(images, standard text, etc) in one place? Or is there an equivalent
> >mechanism in XML?
> >
> >Also, just out of curiousity are you currently using one of these fancy
> new
> >XML editors to create and maintain your EAD XML?
> >
> >Ed Summers
> >Old Dominion University
> >
> >
> Daniel V. Pitti         Project Director
> Institute for Advanced Technology in the Humanities
> Alderman Library        University of Virginia  Charlottesville, Virginia
> 22903
> Phone: 804 924-6594     Fax: 804 982-2363       Email: [log in to unmask]