Hi all,
we are currently working on the question how to deal with broken links/
references between resources in (distinct) LOD data sets and would
like to know your opinion on that issue. If there is some work going
on into this direction, please let me know.
I think I do not really need to explain the problem. Everybody knows
it from the "human" Web when you follow a link and you get an annoying
404 response.
If we assume that the consumers of LOD data are not humans but
applications, broken links/references are not only "annoying" but
could lead to severe processing errors if an application relies on a
kind of "referential integrity".
Assume we have an LOD data source X exposing resources that describe
images and these images are linked with resources in DBPedia (e.g., http://dbpedia.org/resource/Berlin)
. An application built on-top of X follows links to retrieve the geo-
coordinates in order to display the images on a virtual map. If now,
for some reason, the URL of the linked DB-Pedia resource changes
either because DBPedia is moved or re-organized, which I guess could
happen to any LOD source in a long-term perspective, the application
might crash if doesn't consider that referenced resources might move
or become unavailable.
I know that "cool URIs don't change" but I am not sure if this
assumption holds in practice, especially in a long-term perspective.
For the "human" Web several solutions have been proposed, e.g.,
1.) PURL and DOI services for translating URNs into resolvable URLs
2.) forward references
3.) robust link implementations, i.e., with each link you keep a set
of related search terms to retrieve moved / changed resources
4.) observer / notification mechanisms
X.) ?
I guess (1) is not really applicable for LOD resources because of
scalability and single-point of failure issues. (2) would require that
LOD providers take care of setting up HTTP redirects for their moved
resources - no idea if anybody will do that in reality and how this
can scale. (3) could help to re-locate moved resources via search
engines like Sindice but not really fully automatically. (4) could at
least inform a data source that certain references are broken and it
could remove them.
Another alternative is of course to completely leave the problem to
the application developers, which means that they must consider that a
referenced resource might exist or not. I am not sure about the
practical consequences of that approach, especially if several data
sources are involved, but I have the feeling that it is getting really
complicated if one cannot rely on any kind of referential integrity.
Are there any existing mechanism that can give us at least some basic
feedback about the "quality" of an LOD data source? I think, the
referential integrity could be such a quality property...
Thanks for your input on that issue,
Bernhard
______________________________________________________
Research Group Multimedia Information Systems
Department of Distributed and Multimedia Systems
Faculty of Computer Science
University of Vienna
Postal Address: Liebiggasse 4/3-4, 1010 Vienna, Austria
Phone: +43 1 42 77 39635 Fax: +43 1 4277 39649
E-Mail: [email protected]
WWW: http://www.cs.univie.ac.at/bernhard.haslhofer
