Article category: PBCoreCollection
Use of PBCore in the American Archive Pilot Project
Illinois Public Media was one of the 20-some public TV and Radio stations in the CPB-funded American Archive Pilot Project. The AAPP required participating stations to use PBCore as a metadata format, at least in principle. I decided to push implementation of PBCore in my AAPP content collection as far as possible using the toolset I used on a previous video archive project (Prairiefire on WILL-TV).
This toolset is based on the website Content Management System called ExpressionEngine, which makes setting up a particular database structure rather easy. I set up the database structure based on PBCore elements, with controlled vocabularies reflecting the AAPP taxonomy and suggested PBCore picklists. I then created xml templates in ExpressionEngine to render my AAPP collection metadata as valid PBCore records. I then went one step further, following discussions with Dan Jacobson and David Rice, and created a PBCoreCollection wrapper containing all 235 of the PBCore item records (each as a PBCoreDescriptionDocument) in my collection. The national portal for the AAPP, being developed and hosted at Oregon Public Broadcasting, was able to simply ingest the PBCoreCollection, demonstrating the viability of this approach to aggregating a large collection from multiple content sources.
This article details the methods used to accomplish this in ExpressionEngine. Similar methods could be used in Drupal, which we’re working on now.
In ExpressionEngine, one can easily define a set of fields to input data. For example a blog would need fields for a Title, a Body, and maybe a separate Image upload field along with a label field for the image (so you could add a caption or an alt tag at least). When you create these fields, you also pick a field type: textarea, dropdown list, file upload, etc. EE has several pre-defined field types and there are dozens of addons from third-party developers to add more.
One of the really great EE addons is FieldFrame, developed by Brandon Kelly. FieldFrame is a framework for developing new EE fieldtypes, and there are a bunch of good ones. The most important for our EE PBCore tool is called FF Matrix, which allows you to bundle several fields in a “row” of related data.
Here’s the way you create an FF Matrix field in ExpressionEngine:
With an FF Matrix field, you can do things like enter a PBCore subject tied to a subjectAuthorityUsed, or title along with titleType. Since most of PBCore elements are wrapped in pairs like this, it’s important to solve this in a straightforward way. With FF Matrix, you can enter as many linked pairs as needed, for example with many subject terms you want to have each term wrapped individually along with its corresponding subjectAuthorityUsed.
Here’s the PBCore Item entry form showing a number of such fields (but not the entire form which is a bit long):
We used this form to enter all the Intellectual Content and Intellectual Property metadata for each media item. Nothing in this Item form relates to the physical or digital Instantiation of that item. For that we used a different form with fields and fieldtypes defined specifically for Instantiation metadata. Here’s the fun part: One of the fieldtypes in the Instantiation form is a “relationship” field, which allows you to select an existing Item to which the Instantiation should be linked. So if you have several Instantations, like a wav file, and mp3, and an analog tape of the same Item, you create Instantiations records for each and link them to the Item.
This proved to be a quick and effective way to link multiple Instantiations with a single Item.
You might be able to see that some of the fields are blank, and their instructions say things like “formatDataRate - If MP3 file don’t enter anything.” Lots of the technical metadata like formatFileSize etc could be extracted automatically from the digital files by the system, so we don’t have to enter that data by hand. EE has a nice addon called MP3 Info + that does most of that work.
David Rice has developed better methods of reading file metadata into his PBCore Records Repository using a free tool called MediaInfo. We should get him to write more about that, as it’s work that could be leveraged and used in different systems I’m sure.
After entering all the metadata for our collection using the two forms above, the payoff is in rendering everything in usable form. Since it’s all in the CMS, it’s a simple matter to make a website displaying everything, and providing media players for the files. In fact we did this initially for the catalogers so they could work remotely and listen to and view the audio and video files.
This site was intended for that purpose: http://will.illinois.edu/metadata/aapp-inventory-all/.
As the catalogers added descriptive metadata, the site became much more interesting! We added as much descriptive stuff as possible, even full tape logs for some of the World War II oral history interviews. I chose not to display all that metadata on the web page, but it is rendered in the PBCore XML record for each item.
For example, here is a web page for one such interview: http://will.illinois.edu/metadata/aapp-inventory-all/WWII_oral_history_WesleyMatthews2008-02-21
And here is the PBCore record for the same interview: http://will.illinois.edu/metadata/pbcoreAAPP/wwii_oral_history_wesleymatthews2008-02-21
The way these are rendered is simple: an html template for the web page, and an xml template for the PBCore record, both drawing from the same database. In ExpressionEngine this is very simple to set up, and once it’s set up, you’re done.
Finally, as mentioned above I chose to try implementing the idea of a PBCoreCollection wrapper element, enclosing all 235 of the individual PBCoreDescriptionDocuments in my AAPP media collection. This is, of course, not a valid wrapper element in any PBCore version to date. This experience suggests that it should be. OPB was able to ingest my entire collection in a single gulp from this URL. Other stations in the AAPP were able to export using the same method (PBcoreCollection) even though they have different local systems. The ability to render a PBCoreCollection is all that matters, not the underlying system that rendered it.
I hope this is useful to anyone who might be looking for systems for cataloging media assets and doing various things with them like creating websites and PBCore records or whatever metadata format. I used ExpressionEngine but the basic method would work with Drupal, Plone, and other CMSs and frameworks. Most importantly, regardless of the system used, I hope this demonstration of the power of PBCoreCollection informs the development of PBCore 2.0, which is now in progress.
PBCore Recommendation : PBCoreCollectionOver the last few months, I have worked with Jack Brighton and Dave Rice to have the NPR API (http://www.npr.org/api) output PBCore as a supported format. In the early stages, we were able to put together a mapping of NPRML (our native XML format) to PBCore. From this mapping, my team and I started conceptualizing how this would work within the framework of the API. This exercise ultimately failed because of a philosophical issue between PBCore and the NPR API.
PBCore's implementation focuses on the individual conceptual asset (in NPRML terms, the story). So, if a station wants to receive the 20 stories from today's All Things Considered in PBCore, the station would receive 20 documents, one for each segment (and possibly another document for the program episode record). Meanwhile, the NPR API is a feed-oriented model, which means that a station that wants all 20 ATC segments would make a single request that delivers all 20 items, as well as the information about the program episode. The NPR API model matches many of the more popular feed types in the marketplace, including RSS, ATOM, Podcast, etc.
Because of this key difference, it is a big challenge to fit PBCore into the NPR API model. And because of this difference, I would like to recommend a new implementation to the PBCore schema to allow it to handle its current requests as well as the feed-based requests. Here is a sample of the changes:
<PBCoreCollection xsi:schemaLocation="http://www.pbcore.org/PBCore/PBCoreNamespace.html http://www.pbcore.org/PBCore/PBCoreXSD_Ver_1-2-1.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.pbcore.org/PBCore/PBCoreNamespace.html"> <PBCoreCollectionTitle>Title of this collection of stories </PBCoreCollectionTitle> <PBCoreCollectionDescription>This news feed contains stories that meet all of the following criteria: (1) Stories aired on "All Things Considered". (2) Stories from the "Afghanistan" topic.</PBCoreCollectionDescription> <PBCoreCollectionSource>NPR API <PBCoreCollectionLink>Link back to the source for this feed </PBCoreCollectionLink> <PBCoreCollectionPubdate>Thu, 16 Oct 2008 06:00:00 -0400 </PBCoreCollectionPubdate> <PBCoreDescriptionDocument> <!-- OTHER ELEMENTS GO HERE --> </PBCoreDescriptionDocument> <PBCoreDescriptionDocument> <!-- OTHER ELEMENTS GO HERE --> </PBCoreDescriptionDocument> <PBCoreDescriptionDocument> <!-- OTHER ELEMENTS GO HERE --> </PBCoreDescriptionDocument> </PBCoreCollection>
The key to the recommendation is to wrap all of the current XML in a parent node called <PBCoreCollection>. The namespace attributes, which were previously attached to the <PBCoreDescriptionDocument> element, have been moved up to the collection element.
The <PBCoreCollection> node may then contain several child nodes which describe the collection itself, such as title, description, source, and date (similar to the
The <PBCoreCollection> node may contain any number of iterations of the <PBCoreDescriptionDocument> as sub-nodes.
After describing the collection, the PBCore document will then provide the list of actual documents. For each <PBCoreDescriptionDocument> element in this overall document, I have made no changes (other than lifting the namespace attributes to the collection element).
The purpose of this approach, again, is to enable multiple PBCore documents to be delivered in one transaction as one document. To ensure backward compatibility for existing implementations, they can continue to process each item one at a time in this model as well by having only one <PBCoreDescriptionDocument>. That said, I believe that PBCore should recommend to implementers that they use of the feed-based approach. The most expensive part of data transfer from one system to another is always going to be the transaction itself, not the parsing of the document. So, for those 20 ATC segments, performing those 20 transactions and parsing them individually is far less efficient than doing one transaction and parsing the larger document.
Jack, Dave and I have also discussed potential conflicts with some current implementations that handle the transferring of multiple documents differently. So, if one system currently zips up multiple documents and another sends them individually, these two systems may not be able to work together without custom development, even though both of them are currently complying with the PBCore standard. Extending the standard to provide a method for distribution of multiple documents would also standardize the development practices around distribution of PBCore documents.
The three of us have had many conversations about <PBCoreCollection> and see great merit in this schematic change for PBCore. Although NPR is the real-life scenario that has surfaced this proposal, we believe that the merit of this approach goes far beyond working within the NPR framework.
Although we have put together this proposed model, we know that there are other great minds that could help us refine the recommendation. We look to forward your feedback and to an engaging discussion!