Topic 1: What do we mean by "GUID"?

Patricia Mergen p_mergen at YAHOO.COM
Tue Oct 11 12:09:23 CEST 2005

Dear Donald and colleagues from the GUID group

Please find some comments here below

There are two concepts which may be kept separated:
        Identify an “item” (object or representations of the
object) which should be unique and stable which can be
understood as a GUID.
        Localisation of an object or its representation which
may and often is not stable.

Many of the tools and systems suggested  so far often
mix up these two concepts and intend to identify and
localise at the same time. Problems than occur often
because localisation is not stable and apparently not
workable as a GUID.

Maybe for solving the problem, we could try for
GBIF/TDWG to keep these two concepts separated and
look for a system which is most appropriate to
identify uniquely and in a stable way the unit level
data. This can be an Accession number with no meaning
like those used for Sequence data.
Localisation of the object can be dealt with as being
information about the “object” that can change in time
like any other.

Best regards

Patricia Mergen
--- Donald Hobern <dhobern at GBIF.ORG> wrote:

> [ I will be trying to provide some structure to
> discussions in this mailing
> list by raising specific topics and looking for
> comments.  Please keep the
> Topic number in responses ]
> Topic 1: What do we mean by GUID?
> The most fundamental thing that we need to establish
> as we consider a GUID
> implementation is a definition for "GUID" in this
> context.  We have been
> using a number of terms to describe the identifiers
> we need (unique,
> resolvable, persistent, etc.).
> I've been spending some time following up on Rod
> Page's recommendation that
> we consider the use of Archival Resource Keys (ARK)
> from the California
> Digital Library (see
> The CDL web site includes an excellent overview of
> this GUID model, which
> also serves as an excellent introduction to the
> issues involved.  I would
> urge you all to read this document - it's only nine
> pages long!):
> This document arrives at the following problem
> definition for persistent,
> actionable identifiers:
> 1.      The goal: long-term actionable identifiers.
> a.      Requirement: that identifiers deliver you to
> objects (where
> feasible).
> b.      Requirement: that identifiers deliver you to
> object metadata.
> c.      Desirable: each object should wear its own
> identifier.
> d.      Requirement: that identifiers deliver you to
> statements of
> commitment.
> 2.      The problem: URLs break for some objects
> (that is, associations
> between URLs and objects are not maintained), and we
> have no way to tell
> which ones will or won't break.
> 3.      Why URLs break: because objects are moved,
> removed, and replaced -
> completely normal activities - and the provider in
> each case demonstrates
> insufficient commitment to update indirection
> tables, or to plan identifier
> assignment carefully. Persistence is in the mission
> of few organizations.
> 4.      Conventional hypothesis: use indirect names
> (PURLs, URNs, Handles)
> instead of URLs; what worked for DNS should work for
> digital object
> references.  Wrong. Indirection is spectacularly
> successful and elegant in
> DNS, but it's a side issue in the provision of
> digital object persistence.
> This document clearly identifies issues around
> provider service commitments
> as the key problem that needs solving.  The
> construction of ARKs seeks to
> address this in a couple of ways.  It separates the
> role of Name Assigning
> Authority (i.e. who initially assigns the
> identifier) from that of the Name
> Mapping Authority (i.e. who is able to map the
> identifier to the data object
> at any particular time).  It also defines a simple
> standard relationship
> between three things: the data object, the metadata
> for the object, and a
> commitment statement from the provider as to what
> aspects of persistence are
> guaranteed.
> ARK is a technology that we have not really
> considered up to this point.  My
> question for discussion is what, if anything, is
> missing or wrong about the
> problem definition provided in this document?  If we
> agree that it provides
> a crisp definition of what we need, that in itself
> will be a major step
> forward.
> Please provide your thoughts.
> Donald
> Donald Hobern (dhobern at
> Programme Officer for Data Access and Database
> Interoperability
> Global Biodiversity Information Facility Secretariat
> Universitetsparken 15, DK-2100 Copenhagen, Denmark
> Tel: +45-35321483   Mobile: +45-28751483   Fax:
> +45-35321480

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