Hi Kate --
The sole purpose of the DTD or schema is to ensure that a file you create is valid against that DTD or schema. The DTD says, "These are the tags and attributes that are allowed in EAD, and you may use them only in these combinations." The schema goes a step further and checks MORE stuff, the sort of stuff that can't easily be built into a DTD. For example, the schema could check whether the value for a given attribute is all lower case, or comes from a predefined list of options, or matches a specific pattern such as the ISO-8601 options for normalized dates.
Generally, a schema-valid file will always be a DTD-valid file, but a DTD-valid file will not necessarily be schema-valid, since the schema is MORE prescriptive than the DTD. So a file exported from Archivists' Toolkit should always be DTD-valid but may not be schema-valid.
Because the DTD's/schema's only purpose is to validate a file, which one you use is irrelevant to a file's interaction with other applications, except insofar as that other application might (for example) expect or require a particular attribute to be in all caps and you could use the schema to enforce that.
As to ContentDM, you might want to look at this http://ir.uiowa.edu/cdm_mw2010/2010/april8/1/ , a presentation on Marquette's experience testing CDM and EAD in 2010.
We don't use CDM for our finding aids and it's been a while since I looked at it, so this could have changed, but I'm pretty sure that once a finding aid is ContentDM you can't edit it; if you need to change the finding aid you have to delete the one in CDM and re-import it afresh. When you do that, the new version has a different URL, so any links to the old finding aid will be dead. Depending on your workflow and publishing path, of course, that may not matter, but it's something to be aware of. If you're doing a lot of cross-linking of finding aids in the Related Materials section it could cause you some hiccups down the road.
Hope this helps --
From: Encoded Archival Description List [mailto:[log in to unmask]] On Behalf Of Blalack, Kate
Sent: Tuesday, March 06, 2012 5:03 PM
To: [log in to unmask]
Subject: CONTENTdm and DTD and Schema mechanics
We are currently exporting our finding aids into EAD using Archivists Toolkit, making a few minor adjustments and uploading them into CONTENTdm. Has anyone else used CONTENTdm to display their finding aids? If so would you mind exchanging ideas with me off list? Or, on the list, if this is of interest to the whole.
In the past I was a little unclear about the differences between the DTD and the schema and how they work with EAD. In some ways I am still unclear about the mechanics of it all (behind the scenes), because I am not from an IT background. How does the DTD or Schema effect the xml's interaction with various software packages? I know this is a question that has probably been discussed before but not while I have been here. I wonder if anyone can offer some clarification about this. It's always good to have a refresher.
Thank you in advance for your help, ideas and advice!