Makes my head hurt

I was talking with Diane this morning about building the schema portion of the Registry and I feel the need to write down some of what we discussed.

For purposes of discussion, we have a draft schema property interface that defines some basic metadata schema property properties. We started the conversation because I was trying to get away from the “property property” nomenclature and because I couldn’t quite figure out the best way to extend the too-simple model to incorporate repeatable, typed notes/annotations.

Over the course of the discussion we came to a few conclusions:

• What we’re really discussing is an Application Profile in the old DC sense of that term (it has since been changed to “Description Set Profile” to reflect the more DCAM-centric viewpoint of the current DC Community) in which we’re defining schema property restrictions, namespaces, and usage requirements: There can be only one token, definition, label, type and they’re required; ‘Type’ utilizes a controlled vocabulary containing the concepts ‘property’ and ’subproperty’; etc.
• We have a Schema Properties Vocabulary registered that identifies these schema property description ‘terms’ as ‘concepts’, but this isn’t really correct because they’re actually properties of a metadata schema ‘property’ (and so we’re back to property properties <sigh>) and as such they should be registered as an Application Profile rather than a Vocabulary.
• The properties of each schema we register should be based on its own Application Profile, since there will be many different requirements and we’d like to provide some flexibility. For instance the RDA schema may need to have an additional property property that declares a relationship between the property and a FRBR entity.
• We can’t register a Metadata Schema Properties Application Profile until we can register a Schema
• In order to register a metadata schema we need a generic Metadata Schema Properties Application Profile
• We’re stuck with “property properties”
• This stuff makes my head hurt

In the interest of moving forward, stopping the spinning, and headache relief we’re going to pretend that a generic Metadata Schema Property Application Profile (MSPAP — pronounced ‘ems-pap’) exists and slap something together and make the interface fairly inflexibly tied to it. At some point in the future we’ll (hopefully) make it flexible enough to be based on any registered MSPAP.

TimeSlices and Versions

You can now retrieve a snapshot in time of the RDF or XSD serialization of a Concept/Scheme/Vocabulary by appending a ‘TimeSlice’ to the URI. For example:

http://metadataregistry.org/uri/NSDLEdLvl/ts/20060422200002.rdf
or
http://metadataregistry.org/uri/NSDLEdLvl/ts/20060422200002.xsd

will always and forever retrieve the SKOS/RDF or XML Schema representation of the NSDL Ed Level Vocabulary as it appeared at 2 seconds after 8PM on April 22, 2006 (2006-04-22 20:00:02). If you follow the above .rdf link you’ll notice that the concept URIs that the TimeSliced Vocabulary references have also had a TimeSlice appended:

http://metadataregistry.org/uri/NSDLEdLvl/1001/ts/20060422200002.rdf

in order to lock them into that precise point in time on an individual basis as well. We hope the utility of being able to reference a vocabulary at a particular point in time regardless of subsequent changes will be, well, useful.

In order to make retrieving TimeSlices for specific events in the history of a vocabulary a bit handier, we added a TimeSlice link to every history event. You can specify a TimeSlice for any point in time regardless of its relationship to a history event, but the link just makes it simpler (it’s over on the right side of each line):

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Named Versions

You’ll maybe also have noticed that there’s a ‘Name’ link nestled to the right of the RDF and XSD links. If you’re a Vocabulary Administrator, then you now have the ability to label a TimeSlice with a distinct version name. That link again is there to make it easy to reference a point in historical time and clicking on it pre-enters that TimeSlice into the Create new version form:

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There’s no limit to the number of versions you can create, and versions (unlike TimeSlices) can be deleted or edited by any Vocabulary Admin:

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…although we think that either editing or deleting a version is likely to be a less-than-ideal practice. Still, we allow it — it’s your vocabulary after all.

Once a named version has been associated with a TimeSlice, it will appear in the event history list just above the point in time it references:

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The RDF and XSD links on the right side of the version line now reference the version name:

http://metadataregistry.org/uri/NSDLEdLvl/version/release+1.0.rdf

But this is where it gets a little incorrect… Since the named version URL is just a TimeSlice reference, it does a silent redirect to the referenced TimeSlice. It should probably do a 303 redirect instead. We’ll fix this later, unless it’s a show-stopper for one of our many users.

Improved user management

We’ve been promising for a while now that we’d make it easier, actually a better word is ‘possible’, for Vocabulary Owners to add ‘Members’ to Owner/Agents and ‘Maintainers’ to Vocabularies. We finally implemented it today! It’s unfortunate that it has taken us so long, since one of the primary goals of the Registry is to support multi-user vocabulary development, but it turned out to require more infrastructure twiddling than we thought it would.

If you’re a vocabulary owner and are logged in, you can add other registered folks as ‘members’ of your Owner/Agent and you can even make them administrators if you want:

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We hope the process is pretty self-explanatory.

Once you’ve added a user as a member of your Owner/Agent group, you can add them to your vocabularies as Vocabulary Maintainers or Administrators.

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We realize that this is still somewhat limited and of course the documentation is ummm, poor, but we’ll be doing more with user management shortly.

Registry News

We’ve updated the front page of the Registry to include a Registry-specific news feed from the Registry blog. You can subscribe to it right from (t)here and stay up-to-date with the Registry as we move it forward. Notes like this will be typical and probably pretty frequent over the next few months.

Major update

The registry database was updated last week, in both the sandbox and the registry, to support history tracking. This is in preparation for finally enabling timeslice retrieval and versioning.We also made some significant changes to the site layout and css, so if things still look a little funky, try refreshing your browser — most browsers seem to be caching our css and not detecting the changed files.In the process, we broke search (you may not have even noticed), but it’s fixed now.

New Host

Since the beginning of the project, we’ve been running our own web server. After a significant number of local service outages on the part of Time Warner this year, particularly in July, we finally decided that had to change.

As of today, we’re running on Dreamhost. Dreamhost isn’t perfect, but they offer a nice package of services, reasonably good support and, with the right promo code, the price was right. So we’re going to give it a try for a while.

Moving from a host where we had complete control of the Apache and MySql servers to a shared host where we don’t has required some minor configuration changes to the blog and the wiki, and some significant changes to trac and subversion, but no changes to the Registry. As a side effect of the wiki tweak, we can have prettier URLs — http://metadataregistry.org/wiki/index.php?title=Main_Page becomes http://metadataregistry.org/wiki/Main_Page. Links will default to the new style, although the older form will still work in order to keep older bookmarks working too.

We updated trac and subversion to the latest stable releases, moved trac from a lighttpd server to Apache and moved subversion from a subversion server to Apache as well. This has changed the user authentication process for both services, hopefully for the better.

Registry update

We made some major/minor changes to the Registry software last week. If you’ve used it lately you may have noticed the fairly ugly tabs that replaced the links at the top of the browse pages. They still need some work, but it’s generally a lower priority than some other things.

The major change was reworking a significant amount of the Registry code to bring it up to the Symfony 1.0 release. We’d been working with a fairly ancient version of Symfony while waiting for the final and as a result there were significant structural changes required. We also wrote a bunch of automated functional tests so that we can be a bit more confident that future releases will have fewer bugs. You shouldn’t notice any of this when using the Registry, but please let us know if we broke anything.

We cleared up a few small existing bugs, one of which was that the Registry was a little too aggressive in checking to see if a prefLabel was unique, so the check is now local to the Vocabulary instead of the entire Registry. Another was that under some circumstances the URIs generated by the Registry Sandbox had a hard-to-see double slash after the base domain, causing the URIs to fail to resolve properly. In addition to fixing the bug we also fixed all of the bad existing URIs.

More updates are imminent.