iDigBio: You are putting identifiers on the wrong thing

The Integrated Digitized Biocollections (iDigBio) project aims to advance digitising US biodiversity collections. They recently published a GUID Guide for Data Providers. In the PDF document I read this:

It has been agreed by the iDigBio community that the identifier represents the digital record (database record) of the specimen not the specimen itself. Unlike the barcode that would be on the physical specimen, for instance, the GUID uniquely represents the digital record only. (emphasis added)

My heart sank. There's nothing wrong with having identifiers for metadata (apart from inviting the death spiral that is metadata about metadata), but surely the key to integrating specimens with other biodiversity data is to have globally unique identifiers for the specimens.

Now, identifiers for metadata can be useful. For example, there is a specimen of Parathemisto japonica in the National Museum of Natural History, Smithsonian Institution with the label "USNM 100988". The NMNH web site has a picture of the index card for this specimen:



This is an image of the metadata, not the specimen itself. We could link the metadata to this image, but of course we also want to link it to the actual specimen.

Specimens are the things we collect, preserve, dissect, measure, sequence, photograph, and so on. I want to link a specimen to the sequences that have been obtains from that specimen, I want to list the publications that cite that specimen, I want to be able to aggregate data on a specimen from multiple sources, I want to be able to add annotations including misidentifications, simple typos, or missing georeferencing.

Key to this is having identifiers for specimens. Identifiers for metadata about those specimens is not good enough. By analogy with bibliographic citation, one of the important decisions CrossRef made was that DOIs for articles identify the article, not the metadata about the article, or any of the different formats (HTML, PDF, print) and article may occur in. This means we can build databases about things and relationships (this article cites that one, these articles were authored by this person, etc.).

As it stands, if we don't have identifiers for specimens then we can't link data together. For example, the frog specimen "USNM 195785" is depicted in the image below (from EOL):



It is also listed in various papers in BioStor. In the absence of a globally unique identifier for this specimen how do I make these links? "USNM 195785" won't do because there are at least four specimens in the USNM with the catalogue number "195785". The GBIF occurrence id for this specimen (http://data.gbif.org/occurrences/244405570) would be an obvious candidate, were it not for the fact that GBIF has no concept of stable identifiers and its occurrence ids regularly change.

I confess I'm flabbergasted that iDigBio has avoid tackling the issue of specimen identifiers. If any museum wants to discover how its collection is being used to support science it will want to find the citations of its specimens in scientific papers and databases. This requires identifiers for specimens.

Quick thoughts on specimen identifiers

Based on recent discussions my sense is that our community will continue to thrash the issue of identifiers to death, repeating many of the debates that have gone on (and will go on) in other areas. To be trite, it seems to me we have three criteria: cheap, resolvable, and persistent. We get to pick two.

Cheap and resolvable means URLs, which everybody is nervous about because they break. They don't have to break, but for a bunch of reasons they do.

Cheap and persistent means things like Darwin Triplet Core or URNs. You can write things on paper and they will persist (the Biodiversity Heritage Library shows us that), but how in the digital era do we do anything with this? If it's not resolvable what, exactly, is the point? We tried URNs — even ones that were resolvable (LSIDs) — and that was a disaster (we learnt a lot, but what a mess).

Resolvable and persistent. This is where technologies such as DOIs reside. If every specimen had a DOI would we still be having this discussion? We'd have a resolvable identifier that is resistant to change (including loss of museum domain names, specimens moving to new institutions, etc.), and one that is already in use by CrossRef and DataCite, and will also play ball with linked data folks.

In practical terms, what if we had a convention that each collection gets it's own DOI prefix "10.nnnn", after which it appends whatever specimen identifier makes sense (and is unique within that collection).

The bulk of specimen identifiers in the wild are of the form "Institution" "Catalogue number", e.g. ANSP 332467 (from the example I discussed in BHL and GBIF as biomedical databases).

If we wrote this as a DOI of the form <doi prefix>/Collection/InstitutionCatalogue number then we'd have identifiers that (in part) matched what most people would expect to see. In the example above we would have something like:

10.nnnnn/MAL/ANSP332467

where "MAL" is the acronym for the Malacology collection. This is pretty close to "ANSP 332467", is human friendly, but would also be resolvable. It also carries limited branding, so if the specimen was moved from it's current collection to a new institution, people wouldn't get too upset by the presence of "ANSP"). It would also help make the links between specimen codes and DOIs. We couldn't rely on 10.nnnnn/MAL/ANSP332467 being a specimen in the Academy of Natural Sciences's malacological collection, but it would be a good place to start looking.

As I've argued before, we could centralise the minting of these identifiers using GBIF, but do it in a such a way that host institutions could assume responsibility for it if and when they are able (i.e., initially GBIF is responsible for managing the DOI prefixes for each institution, with the option for institutions to do this). The beauty of identifiers like DOIs is that from the user's perspective the identifier is unchanged.

I'm hoping we'll make some progress on this in the coming months...

Yet another reason why we need specimen identifiers, now!

This message appeared on the TAXACOM mailing list:

It is getting more and more necessary for taxonomists to demonstrate
that they are useful and used. This does not only apply to the
individual scientists, but also to institutions with taxonomic
collections, such as museums and herbaria.

In an attempt to live up to that increasing demand for documentation,
the leadership of the Natural History Museum of Denmark has issued an
order to its curatorial staff - The staff members are requested to
document which publications from 2011, written entirely by external
scientists, that in one way or another are based on material in the
collections of the Museum.

Given that most specimens lack resolvable digital identifiers (a theme I've harped on about before, most recently in the context of DNA barcoding), answering this kind of query ends up being a case of searching publications for text strings that contain the acronym of the collection. The sender of the message, Ib Friis, is alarmed at this prospect:

In publications, material from our herbarium at "C" is normally referred
to in text strings of one of the following forms: "(C)", "(C, ", ", C,"
or " C)". But a search in for example Google Scholar or other search
engines result in overflow of thousands and thousands of hits, even
when these text strings are combined with other relevant words such as
"botany", "plants", etc.

In an earlier paper "Biodiversity informatics: the challenge of linking data and the role of shared identifiers" (http://dx.doi.org/10.1093/bib/bbn022) (free preprint available here: hdl:10101/npre.2008.1760.1) I argued that having resolvable identifiers for specimens could enable measures of "citation" to be computed for specimens (and data derived from those specimens). Just as we have citation counts for articles and impact factors for journals, we could have equivalent measures for specimens and collections. These measures may keep administrators happy, for scientists I think the real benefits will be the ability to trace the provenance of some data, and the fate of data they themselves have collected or published.

For things such as publications it is trivial to track their usage. For example, to find the number of times the article "Biodiversity informatics: the challenge of linking data and the role of shared identifiers" has been cited, I simply enter the DOI into Google Scholar, e.g. http://scholar.google.co.uk/scholar?q=10.1093/bib/bbn022. Imagine being able to do the same for specimens?

For this to happen, museum specimens need digital identifiers. If museums are serious about quantifying the impact of their collections, they should make assigning digital identifiers a priority.

DNA Barcoding, the Darwin Core Triplet, and failing to learn from past mistakes

Given various discussions about identifiers, dark taxa, and DNA barcoding that have been swirling around the last few weeks, there's one notion that is starting to bug me more and more. It's the "Darwin Core triplet", which creates identifiers for voucher specimens in the form <institution-code>:<OPTIONAL collection-code>:<specimen-id>. For example,

MVZ:Herp:246033

is the identifier for specimen 246033 in the Herpetology collection of the Museum of Vertebrate Zoology (see http://arctos.database.museum/guid/MVZ:Herp:246033).

On the face of it this seems a perfectly reasonable idea, and goes some way towards addressing the problem of linking GenBank sequences to vouchers (see, for example, http://dx.doi.org/10.1016/j.ympev.2009.04.016, preprint at PubMed Central). But I'd argue that this is a hack, and one which potentially will create the same sort of mess that citation linking was in before the widespread use of DOIs. In other words, it's a fudge to postpone adopting what we really need, namely persistent resolvable identifiers for specimens.

In many ways the Darwin Core triplet is analogous to an article citation of the form <journal>, <volume>:<starting page>. In order to go from this "triplet" to the digital version of the article we've ended up with OpenURL resolvers, which are basically web services that take this triple and (hopefully) return a link. In practice building OpenURL resolvers gets tricky, not least because you have to deal with ambiguities in the <journal> field. Journal names are often abbreviated, and there are various ways those abbreviations can be constructed. This leads to lists of standard abbreviations of journals and/or tools to map these to standard identifiers for journals, such as ISSNs.

This should sound familiar to anybody dealing with specimens. Databases such as the Registry of Biological Repositories and the Biodiversity Collectuons Index have been created to provide standardised lists of collection abbreviations (such as MVZ = Museum of Vertebrate Zoology). Indeed, one could easily argue that the what we need is an OpenURL for specimens (and I've done exactly that).

As much as there are advantages to OpenURL (nicely articulated in Eric Hellman's post When shall we link?), ultimately this will end in tears. Linking mechanisms that depend on metadata (such as museum acronyms and specimen codes, or journal names) are prone to break as the metadata changes. In the case of journals, publishers can rename entire back catalogues and change the corresponding metadata (see Orwellian metadata: making journals disappear), journals can be renamed, merged, or moved to new publishers. In the same way, museums can be rebranded, specimens moved to new institutions, etc. By using a metadata-based identifier we are storing up a world of hurt for someone in the future. Why don't we look at the publishing industry and learn from them? By having unique, resolvable, widely adopted identifiers (in this case DOIs) scientific publishers have created an infrastructure we now take for granted. I can read a paper online, and follow the citations by clicking on the DOIs. It's seamless and by and large it works.

On could argue that a big advantage of the Darwin Core triplet is that it can identify a specimen even if it doesn't have a web presence (which is another way of saying that maybe it doesn't have a web presence now, but it might in the future). But for me this is the crux of the matter. Why don't these specimens have a web presence? Why is it the case that biodiversity informatics has failed to tackle this? It seems crazy that in the context of digital data (DNA sequences) and digital databases (GenBank) we are constructing unresolvable text strings as identifiers.

But, of course, much of the specimen data we care about is online, in the form of aggregated records hosted by GBIF. It would be technically trivial for GBIF to assign a decent identifier to these (for example, a DOI) and we could complete the link between sequence and specimen. There are ways this could be done such that these identifiers could be passed on to the home institutions if and when they have the infrastructure to do it (see GBIF and Handles: admitting that "distributed" begets "centralized").

But for now, we seem determined to postpone having resolvable identifiers for specimens. The Darwin Core triplet may seem a pragmatic solution to the lack of specimen identifiers, but it seems to me it's simply postponing the day we actually get serious about this problem.