[Tdwg-tag] TCS in RDF for use in LSIDs and possible generic mechanism.
roger at tdwg.org
Mon Mar 20 14:35:57 CET 2006
I am cross posting this to the TCS list and the TAG list because it is
relevant to both but responses should fall neatly into things to do with
nomenclature (for the TCS list) and things to do with technology - for
the TAG list. The bit about avowed serializations of RDF below are TAG
The move towards using LSIDs and the implied use of RDF for metadata has
lead to the question: "Can we do TCS is RDF?". I have put together a
package of files to encode the TaxonName part of TCS as an RDF
vocabulary. It is not 100% complete but could form the basis of a solution.
You can download it here:
For the impatient you can see a summary of the vocabulary here:
and an example xml document here:
It has actually been quite easy (though time consuming) to represent the
semantics in the TCS XML Schema as RDF. Generally elements within the
TaxonName element have become properties of the TaxonName class with
some minor name changes. Several other classes were needed to represent
NomenclaturalNotes and Typification events. The only difficult part was
with Typification. A nomenclatural type is both a property of a name
and, if it is a lectotype, a separate object that merely references a
type and a name. The result is a compromise in an object that can be
embedded as a property. I use instances for controlled vocabularies that
may be controversial or may not.
What is lost in only using RDFS is control over validation. It is not
possible to specify that certain combinations of properties are
permissible and certain not. There are two approaches to adding more
An OWL ontology could be built that makes assertions about the items in
the RDF ontology. It would be possible to use necessary and sufficient
properties to assert that instances of TaxonName are valid members of an
OWL class for BotanicalSubspeciesName for example. In fact far more
control could be introduced in this way than is present in the current
XML Schema. What is important to note is that any such OWL ontology
could be separate from the common vocabulary suggested here. Different
users could develop their own ontologies for their own purposes. This is
a good thing as it is probably impossible to come up with a single,
agreed ontology that handles the full complexity of the domain.
I would argue strongly that we should not build a single central
ontology that summarizes all we know about nomenclature - we couldn't do
it within my lifetime :)
Because RDF can be serialized as XML it is possible for an XML document
to both validate against an XML Schema AND be valid RDF. This may be a
useful generic solution so I'll explain it here in an attempt to make it
accessible to those not familiar with the technology.
The same RDF data can be serialized in XML in many ways and different
code libraries will do it differently though all code libraries can read
the serializations produced by others. It is possible to pick one of the
ways of serializing a particular set of RDF data and design a XML Schema
to validate the resulting structure. I am stuck for a way to describe
this so I am going to use the term 'avowed serialization' (Avowed means
'openly declared') as opposed to 'arbitrary serialization'. This is the
approach taken by the prismstandard.org
<http://www.prismstandard.org>group for their standard and it gives a
number of benefits as a bridging technology:
1. Publishing applications that are not RDF aware (even simple
scripts) can produce regular XML Schema validated XML documents
that just happen to also be RDF compliant.
2. Consuming applications can assume that all data is just RDF and
not worry about the particular XML Schema used. These are the
applications that are likely to have to merge different kinds of
data from different suppliers so they benefit most from treating
it like RDF.
3. Because it is regular structured XML it can be transformed using
XSLT into other document formats such as 'legacy' non-RDF
compliant structures - if required.
There is one direction that data would not flow without some effort. The
same data published in an arbitrary serialization rather than the avowed
one could be transformed, probably via several XSLT steps, into the
avowed serialization and therefore made available to legacy applications
using 3 above. This may not be worth the bother or may be useful. Some
of the code involved would be generic to all transformations so may not
be too great. It would certainly be possible for restricted data sets.
To demonstrate this instance.xml is included in the package along with
avowed.xsd and two supporting files. instance.xml will validate against
avowed.xsd and parse correctly in the w3c RDF parser.
I have not provided XSLT to convert instance.xml to the TCS standard
format though I believe it could be done quite easily if required.
Converting arbitrary documents from the current TCS to the structure
represented in avowed.xsd would be more tricky but feasible and
certainly possible for restricted uses of the schema that are typical
from individual data suppliers.
This is what the files in this package are:
README.txt = this file
TaxonNames.rdfs = An RDF vocabulary that represents TCS TaxonNames object.
TaxonNames.html = Documentation from TaxonNames.rdfs - much more readable.
instance.xml = an example of an XML document that is RDF compliant use
of the vocabulary and XML Schema compliant.
avowed.xsd = XML Schema that instance.xml validates against.
dc.xsd = XML Schema that is used by avowed.xsd.
taxonnames.xsd = XML Schema that is used by avowed.xsd.
rdf2html.css = the style formatting for TaxonNames.html
rdfs2html.xsl = XSLT style sheet to generate docs from TaxonNames.rdfs
tcs_1.01.xsd = the TCS XML Schema for reference.
Needs for other Vocabularies
What is obvious looking at the vocabulary for TaxonNames here is that we
need vocabularies for people, teams of people, literature and specimens
as soon as possible.
Need for conventions
In order for all exchanged objects to be discoverable in a reasonable
way we need to have conventions on the use of rdfs:label for Classes and
Properties and dc:title for instances.
The namespaces used in these examples are fantasy as we have not
finalized them yet.
Minor changes in TCS
There are a few points where I have intentionally not followed TCS 1.01
(there are probably others where it is accidental).
* basionym is a direct pointer to a TaxonName rather than a
NomenclaturalNote. I couldn't see why it was a nomenclatural note
in the 1.01 version as it is a simple pointer to a name.
* changed name of genus element to genusEpithet property. The
contents of the element are not to be used alone and are not a
genus name in themselves (uninomial should be used in this case)
so genusEpithet is more appropriate - even if it is not common
* Addition of referenceTo property. The vocabulary may be used to
mark up an occurrence of a name that is not a publishing of a new
name. In these cases the thing being marked up is actually a
pointer to another object, either a TaxonName issued by a
nomenclator or a TaxonConcept. In these cases we need to have a
reference field. Here is an example (assuming namespace)
This could possibly appear in a XHTML document for example.
All this amounts to a complex suggestion of how things could be done.
i.e. we develop central vocabularies that go no further than RDFS but
permit exchange and validation of data using avowed serializations and
What do you think?
Taxonomic Databases Working Group
roger at tdwg.org
+44 1578 722782
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