One minor correction to Mark's very interesting and useful extptr example. 
The value of the extptr's linktype or (xlink:type, in the W3C and RelaxNG 
versions of EAD) is fixed to "simple", so "locator" would throw a 
validation error. However, I believe things would be fine if the type were 
"simple" rather than "locator".

Also, to offer an extension to what Mark proposed, if one wanted to make 
clear what the thing pointed to in the exptr href is, the role/xlink:role 
attribute could be used. Ideally this would be a URI, but the Tag Library 
doesn't specify this and neither does the DTD/schema, so a locally 
controlled string value (e.g., "OSGBGridRef") wouldn't be formally 

Hope this helps,


  On Thu, 6 May 
2010, Daniel Pitti wrote:

> I prefer the method described below by Mark, as the Ordnance Survey should 
> have all of the data you need, authoritatively maintained. Assuming the URI 
> is persistent and that you reference Bristol more than once in one or more 
> finding aids, it will be more efficient with respect to maintenance.
> On May 6, 2010, at 3:16 PM, Mark A. Matienzo wrote:
>> On Thu, May 6, 2010 at 12:18 PM, Jane Stevenson
>> <[log in to unmask]> wrote:
>>> I'll look at using authfilenumber. Maybe something like:
>>> <geogname rules="ncarules" authfilenumber="ST590730">Bristol</geogname>
>>> But specifying a source here would mean it applies to the place name, not
>>> the grid reference.  I'm not sure how to provide the source/rules for 
>>> both,
>>> as they are different.
>> Right, that's a good point. You could also use a method using the URI
>> method, perhaps something like:
>> <geogname rules="ncarules">
>> Bristol
>> <extptr linktype="locator" actuate="actuatenone" show="shownone"
>>   href=""/>
>> </geogname>
>> ** Note that this example URI isn't valid, as the Ordnance Survey
>> hasn't yet provided a URI structure for 100 m grid references. 1 km
>> grid references are valid, however.
>> Mark A. Matienzo
>> Digital Archivist, Manuscripts and Archives
>> Yale University Library

Terry Catapano
Special Collections Analyst/Librarian
Columbia University Libraries Digital Program
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