Sustainable governance for long-term preservation of RDF Vocabularies

Discussion paper for a special session at DC-2013, Lisbon, 3 September 2013

http://wiki.dublincore.org/index.php/Vocabulary_Preservation_discussion_paper
   Authors: Tom Baker, Bernard Vatant, Pierre-Yves Vandenbussche

Special session is jointly sponsored by W3C and DCMI
   http://dcevents.dublincore.org/IntConf/index/pages/view/vocPres

As a foundation for data sources meant to be usable in the long term,
the value of any given vocabulary depends on the perceived certainty
that the vocabulary -- in both its machine-readable and human-readable
forms -- will remain reliably accessible over time and that its URIs
will not be sold, re-purposed, or simply forgotten. Vocabulary
maintainers move on to other projects or retire. Resources owned by
institutions may be neglected or become unavailable. As the givers of
meaning to datasets, vocabularies are of vital importance to the
scholarly record and cultural memory. However, their preservation will
not happen automatically; it must be planned.

Requirements for long-term preservation of RDF vocabularies

The requirements for long-term preservation must consider a timeframe
that stretches beyond the planning horizon of any institution that
exists today:

 * Institutional guarantees for the persistence of URIs. One good
   first step is for owners of URI domains to publish a commitment that
   any URI coined for a term in a vocabulary will be used to refer to
   the same term in perpetuity and will not be repurposed.

 * Persistence of documentation. Each term URI should remain
   resolvable to "namespace documents" -- descriptive documentation in
   HTML and/or machine- readable representations such as RDF schemas.
   Note that "persistent" URIs may redirect to documentation held at
   non-persistent locations. URIs and the associated documentation
   remain "persistent" to the extent that the link between the two is
   maintained as documentation is moved between servers.

 * Appropriate versioning of vocabularies. Vocabularies evolve over
   time and need to be appropriately versioned. One versioning approach
   commonly used on the Web is to assign a dedicated URI per resource
   version (time-specific URI) and support an additional URI from which
   at any moment in time the current resource version is available
   (time-generic URI). This approach can be used for vocabularies.

Towards a solution

 * Cooperation among vocabulary maintainers. Vocabulary maintainers
   can take some measures to address the problem in the form of mutual aid.
   The Friend of a Friend (FOAF) Project, for example -- a vocabulary
   maintained by two private individuals -- has a cooperation agreement with
   the Dublin Core Metadata Initiative (DCMI) whereby DCMI maintains an
   up-to-date snapshot of the FOAF Vocabulary, may temporarily host the
   vocabulary by redirecting FOAF URIs to the DCMI website if needed, and
   could assume maintenance responsibility for the vocabulary if the FOAF
   Project should cease its normal activity [2]. The intent of this
agreement
   is in part to promote the idea of long-term planning in the vocabulary
   maintenance community and to affirm best-practice principles and policies
   for RDF Vocabularies. Other individual vocabulary publishers, or
short-term
   projects, should be able to engage in similar agreements.

 * Cooperation between vocabulary maintainers and memory
   institutions. Creative Commons took off, as an idea, when it
   provided a set of options for standard, well-understood contracts
   detailing bundles of legal choices related to copyright. Imagine a
   menu of commitments about rights and duties regarding rapid
   interventions (e.g., redirecting URIs if disaster strikes) and the
   transfer of Internet domain names and of maintenance responsibility
   in the long-term. The involvement of major players in the Vocabulary
   Ecosystem could help ensure, at a minimum, that the popular
   vocabularies have such mechanisms in place.

 * Flexible cooperation among memory institutions. No institution on
   the planet can possibly guarantee, today, that it will able to honor
   a preservation commitment of decades -- even in the case of the most
   well-endowed and politically secure national libraries. Implementing
   a redundancy strategy for the long-term preservation of vocabularies
   implies a flexible form of governance among memory institutions. A
   robust preservation strategy would embrace memory institutions large
   and small, in countries rich and poor, from the politically
   guaranteed to the politically more fragile and provisional.

 * The principle of "safety through redundancy". The general
   principle is summarized in the acronym for the LOCKSS service: Lots
   Of Copies Keep Stuff Safe (Maniatis et al. 2005). This can be
   achieved by mirroring information caches among multiple
   repositories. This is analogous to how the Internet's Domain Name
   System itself is cached, or indeed how living organisms ensure the
   survival of their genes by copying their genetic information into
   new carriers rather than by defending a single, ultimately mortal,
   cache of information.

 * Redundant caching of vocabularies. Because the software used for
   LOCKSS provides an automated system for sharing caches of digital
   content within a secure, closed peer-to-peer network -- an idea that
   has already been implemented successfully to preserve digitally
   curated journal holdings -- it has been suggested that this
   software, or something like it, could be used to provide mirrored
   caches of vocabularies (Halpin and Baker, 2010). The LOCKSS system
   monitors the integrity of a local information cache by continually
   comparing the local cache to exact copies of that cache held within
   a closed system of partner institutions and sounding an alarm if
   discrepancies arise. It is mathematically very improbable that a
   even a fairly small number of independently maintained information
   caches, e.g., seven, should be compromised by server failures or
   deliberate manipulation in a way that precludes diagnosis and repair.

 * Access to historical versions. Access to temporally appropriate
   versions of an RDF vocabulary can be supported by innovative
   approaches such as the Memento protocol, which access time-specific
   URIs given a time-generic URI and a datetime.

It could be argued that such a strategy should not be unique to the
problem of preserving RDF vocabularies but should hold for many other
types of information. This is true. However, compared to the much larger
problem of preserving the human record as a whole, the problem of
preserving several thousand RDF property-and-class vocabularies is
comparatively more tractable. The goal is worthwhile and practical as a
first step.

[1] http://dcevents.dublincore.org/index.php/IntConf/dc-2013
[2] http://dublincore.org/documents/dcmi-foaf/


-- 
*Bernard Vatant
*
Vocabularies & Data Engineering
Tel :  + 33 (0)9 71 48 84 59
 Skype : bernard.vatant
Blog : the wheel and the hub <http://bvatant.blogspot.com>
Linked Open Vocabularies : lov.okfn.org
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*Mondeca**          **                   *
3 cité Nollez 75018 Paris, France
www.mondeca.com
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Mondeca is co-chairing
Long-term Preservation and Governance of RDF
Vocabularies<http://dcevents.dublincore.org/IntConf/index/pages/view/vocPres>
at Dublin Core Conference