On 15/5/09 18:20, Manu Sporny wrote:
Kristof Zelechovski wrote:
Therefore, link rot is a bigger problem for CURIE
prefixes than for links.
There have been a number of people now that have gone to great lengths
to outline how awful link rot is for CURIEs and the semantic web in
general. This is a flawed conclusion, based on the assumption that there
must be a single vocabulary document in existence, for all time, at one
location. This has also lead to a false requirement that all
vocabularies should be centralized.
Here's the fear:
If a vocabulary document disappears for any reason, then the meaning of
the vocabulary is lost and all triples depending on the lost vocabulary
become useless.
That fear ignores the fact that we have a highly available document
store available to us (the Web). Not only that, but these vocabularies
will be cached (at Google, at Yahoo, at The Wayback Machine, etc.).
IF a vocabulary document disappears, which is highly unlikely for
popular vocabularies - imagine FOAF disappearing overnight, then there
are alternative mechanisms to extract meaning from the triples that will
be left on the web.
Here are just two of the possible solutions to the problem outlined:
- The vocabulary is restored at another URL using a cached copy of the
vocabulary. The site owner of the original vocabulary either re-uses the
vocabulary, or re-directs the vocabulary page to another domain
(somebody that will ensure the vocabulary continues to be provided -
somebody like the W3C).
- RDFa parsers can be given an override list of legacy vocabularies that
will be loaded from disk (from a cached copy). If a cached copy of the
vocabulary cannot be found, it can be re-created from scratch if necessary.
The argument that link rot would cause massive damage to the semantic
web is just not true. Even if there is minor damage caused, it is fairly
easy to recover from it, as outlined above.
A few other points:
1. It's for the community of vocabulary-creators to help each other out
w.r.t. hosting/publishing these: I just nudged a friend to put another 5
years on the DNS rental for a popular namespace. I think we should put a
bit more structure around these kinds of habit, so that popular
namespaces won't drop off the Web through accident.
2. digitally signing the schemas will become part of the story, I'm
sure. While it's a bit fiddly, there are advantages to having other
mechanisms beyond URI de-referencing for knowing where a schema came from
3. Parties worried about external dependencies when using namespaces can
always indirect through their own namespace, whose schema document can
declare subclass/subproperty relations to other URIs
cheers
Dan
