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Public comment period on the PRISM 2.0 draft ends Saturday (Sept. 15) ahead of next week’s WG meeting to review feedback and finalize the spec. (I put in some comments about XMP already. Hope they got that.)

(Update - 2007.09.15: Clean forgot to add in the rdf: namespace to the examples for xmp:Identifier in this post. I’ve now added in that namespace to the markup fragments listed. Also added in a comment here which shows the example in RDF/XML for those who may prefer that over RDF/N3.)

So, as a preliminary to reviewing how a fuller metadata description of a Crossref resource may best be fitted into an XMP packet for embedding into a PDF, let’s just consider how a DOI can be embedded into XMP. And since it’s so much clearer to read let’s just conduct this analysis using RDF/N3. (Life is too short to be spent reading RDF/XML or C++ code. :~)

(And further to Chris Shillum’s comment [(Update - 2007.09.15: Clean forgot to add in the rdf: namespace to the examples for xmp:Identifier in this post. I’ve now added in that namespace to the markup fragments listed. Also added in a comment here which shows the example in RDF/XML for those who may prefer that over RDF/N3.)

So, as a preliminary to reviewing how a fuller metadata description of a Crossref resource may best be fitted into an XMP packet for embedding into a PDF, let’s just consider how a DOI can be embedded into XMP. And since it’s so much clearer to read let’s just conduct this analysis using RDF/N3. (Life is too short to be spent reading RDF/XML or C++ code. :~)

(And further to Chris Shillum’s comment]2 on my earlier post Metadata in PDF: 2. Use Cases where he notes that Elsevier are looking to upgrade their markup of DOI in PDF to use XMP, I’m really hoping that Elsevier may have something to bring to the party and share with us. A consensus rendering of DOI within XMP is going to be of benefit to all.)

(Continues.)

You might have been wondering why I’ve been banging on about XMP here. Why the emphasis on one vendor technology on a blog focussed on an industry linking solution? Well, this post is an attempt to answer that.

Four years ago we at Nature Publishing Group, along with a select few early adopters, started up our RSS news feeds. We chose to use RSS 1.0 as the platform of choice which allowed us to embed a rich metadata term set using multiple schemas - especially Dublin Core and PRISM. We evangelized this much at the time and published documents on XML.com (Jul. ’03) and in D-Lib Magazine (Dec. ’04) as well as speaking about this at various meetings and blogging about it. Since that time many more publishers have come on board and now provide RSS routinely, many of them choosing to enrich their feeds with metadata.

Well, RSS can be seen in hindsight as being the First Wave of projecting a web presence beyond the content platform using standard markup formats. With this embedded metadata a publisher can expand their web footprint and allow users to link back to their content server.

Now, XMP with its potential for embedding metadata in rich media can be seen as a Second Wave. Media assets distributed over the network can now carry along their own metadata and identity which can be leveraged by third-party applications to provide interesting new functionalities and link-back capability. Again a projection of web presence.

(Continues.)

What on earth can this string mean: ‘W5M0MpCehiHzreSzNTczkc9d’? This occurs in the XMP packet header:

Well from the XMP Specification (September 2005) which is available here (PDF) there is this text:

“The required id attribute must follow begin. For all packets defined by this version of the syntax, the value of id is the following string: W5M0MpCehiHzreSzNTczkc9d”

(See: 3 XMP Storage Model / XMP Packet Wrapper / Header / Attribute: id)

OK, so it’s no big deal to cut and paste that string, it’s just mighty curious why this cryptic key is needed in an open specification, especially since (contrary to what might be implied by the text) it doesn’t seem to vary with version. (Or hasn’t yet, at any rate - more below.)

Following on from the missing XMP Specification version number discussed in the previous post here below are listed some miscellaneous gripes I’ve got with XMP (on what otherwise is a very promising technology). I would be more than happy to be proved wrong on any of these points.

David Shorthouse and Rod Page have developed some great tools for linking references by tying together a number of services and using the Crossref OpenURL interface amongst other things. See David’s post - Gimme That Scientific Paper Part III and Rod’s post on OpenURL and using ParaTools - “OpenURL and Spiders“.

Unfortunately our planned changes to the Crossref OpenURL interface (the 100 queries per day limit in particular) caused some concern for David (“Crossref Takes a Step Back“) - but make sure you read the comments to see my response!

We decided to drop the 100 per day query limit for the OpenURL interface and there will be no charges for non-commercial use of the interface - https://0-apps-crossref-org.libus.csd.mu.edu/requestaccount/

Boy, was I ever so wrong! Contrary to what I said in yesterday’s post, the new PRISM 2.0 spec does support XMP value type mappings for its terms. See the table below which lists the PRISM basic vocabulary terms and the XMP value types.

Many thanks to Dianne Kennedy and the rest of the PRISM Working Group for having added this support to PRISM 2.0.

(Update - 2007.08.28: I inadvertently missed out the term names in the last example of XMP as RDF/N3 with QNames and have now added these in. Also - a biggie - I said that PRISM had no XMP schema defined. This is actually wrong and as I blogged here today, the new PRISM 2.0 spec does indeed have a mapping of PRISM terms to XMP value types. Should actually have read the spec instead of just blogging about it earlier here. :~)

Having previously stooped to an extremely crass hack for pulling out a document information dictionary from PDFs (for which no apologies are sufficient but it does often work) I feel I should make some kind of amends and mention the wonderful ExifTool by Phil Harvey for reading and writing metadata to media files. This is both a Perl library and command-line application (so it’s cross-platform - a Windows .exe and Mac OS .dmg are also provided.) Besides handling EXIF tags in image files this veritable swissknife of metadata inspectors can also read PDFs for the information dictionary and the document XMP packet. And moreover, intriguingly, can dump the raw (document) XMP packet.

I’m still experimenting with it. There’s quite a number of features to explore. But some preliminary finds are listed below.

Following on from yesterday’s post I just came across this very useful source of information on PDF/A: the PDF/A Conformance Center. This provides links to resources such as this whitepaper PDF/A - A new Standard for Long-Term Archiving, and a number of technical notes, especially Metadata and PDF/A-1(also available as a PDF). (This latter corrects some errors in the ISO standard which are to be redressed in a forthcoming Technical Corrigendum later this year.

So, following up on my recent posts here on Metadata in PDFs (Strategies, Use Cases, Deployment), I finally came across PDF/A and PDF/X, two ISO standardized subsets of PDF. the former (ISO 19005-1:2005) for archiving and the latter (ISO 15929:2002, ISO 15930-1:2001, etc.) for prepress digital data exchange.

Both formats share some common ground such as minimizing surprises between producer and consumer and keeping things open and predictable. But my interest here is specifically in metadata and to see what guidance these standards might provide us. Not unsurprisingly, metadata is a key issue for PDF/A, less so for PDF/X. I’ll discuss PDF/X briefly but the bulk of this post is focussed on PDF/A. See below.