Dear all

Here is a contribution to the identifier debate most of which I have
recently used elsewhere that may be of use in this SIG.

With regard to identifiers I think we have to differentiate between at least
3 types of persistence (and uniqueness) that can get muddled up.

1. persistence of the resource (concept, event or ephemeral thing)
2. persistence of the identifier - resource relationship (this may be many
to 1 but should never be x to many)
3. persistence of the resolvability of the identifier to something else (the
resource, metadata or related information)

1. Everyone seems happy with the idea that the resource may die long before
the identifier-resource relationship dies.

2. Everyone seems happy with the idea that it is important that the
identifier is globally unique and only ever associated with a single thing.

This can be split into the two separate bits:
  a.  namespace governance. There seem to be lots of valid candidates and
some people have their favourite pet namespace. Expressing it in URI syntax
may be helpful. Whether it is IANA registered or not may be important to
some, but if you know it is a Handle for example you have some faith that it
is unique. A possible but unlikely problem is that hdl may be used by others
in identifiers expressed as uri syntax. Between most communities, and any
that follow the UKOLN advice,  hdl will be taken as Handle. If this becomes
a real issue two possible solutions are that another IANA namespace is used
if uri is essential and that hdl gets IANA registration - which seems just a
matter of time?.

  b. governance of the relationship - this is not so easy without some kind
of authority organisation or agreement between organisations. The tendency
is that the relationship is controlled by the publisher/creator of the
identifier. The persistence of this relationship is as strong or as weak as
the creator of the ID makes it. In the UK most people would have some faith
in for example JISC, Becta, e-GU or their successors to maintain the
relative persistence of these relationships - even if the organisations
change their (domain) names or disappear as organisations. So far the use of
URLs has not been reliable as people often change the content at a given
location. By building in the domain name (such as tsoid.org.uk) into the
identifier arguably weakens the chance of persistence.

3. The persistence of the resolution is a very separate issue!
It seems that it is often mixed up with other forms of persistence. In a
similar way that people have regularly mixed up identification and location
at the implementation stage. It is also seems to be often assumed or
expected that:
    a. the resolution capability can or must be built into the (URI?)
expression of the identifier
    b. there will only be a single resolution of the identifier

I think these assumptions are both false but others may disagree??

For example a user/local system may wish to check for resolution of id xxx
via a number of preferred services e.g. in the order
http://www.local.org.uk/mydept/xxx
http://www.bath.ac.uk/xxx
http://www.ukoln.ac.uk/xxx
http:///www.tsoid.org.uk
As last resort if they all fail then if it is known (suspected) to be a
Handle for example try
http://hdl.handle.net/xxx   (if it is known to be a Handle)

The doi 10.1790/712276811646 can already be resolved via several domains
even though they all point to the same place.
It can also be very effective to effect a Google search on xxx rather than
the whole uri (try it with 10.1790/712276811646 for example).

In addition the system may be set up to check one or more digital rights
management services to see if there are any usage restrictions.
http://www.digitalrightsmanager.com/xxx

So when it is said that hdl:10.1790/712276811646 or even just
10.1790/712276811646 is not globally unique then that may be become an
issue, but if if it is known that it is Handle or some other well managed
name space it is not a problem.

But when it is said hdl:10.1790/712276811646 or even just
10.1790/712276811646 is not resolvable **on its own** I would say that is
intended and very desirable.

It is very likely that anyone who exposes the Handle id 10.1790/712276811646
will also prefix it with one or more domains that can resolve it. So the
resolution and identification may be contained in a single uri but the id
and resolution are, and can be, separated.

If the id is a for example a url are there any syntax problems with for
example trying to resolve
http://www.egu.gov.uk/http://www.tsoid.org.uk/xxx ???


Summary
The main (or even sole) purpose of a digital identifier is to maintain the
globally unique persistence of the identifier - resource relationship.

The persistence of the resolution is separate and secondary, but still
important. This resolution may be done independently by multiple communities
or organisations, possibly selected as trusted services by the user. However
the original identifier - resource relationship should preferably have some
core information associated with it that indicates the current or expired
owner of the id-resource relationship and  have an associated URL, so that
there a default resolution, this is already the case for some namespaces
including, but not only, Handle and its subsets such as DOI.

These two kinds of persistence may in practice be dealt with by the same
namespace/methodology in some communities such as JISC if it chooses, but
there are many use cases where they need to be separable.

Hope this helps. Comments on flaws in the arguments very welcome.


Cheers
Mike 7:-D
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Mike Collett, Schemeta
+44 7798 728 747
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www.schemeta.com
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