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103 lines
3.9 KiB
103 lines
3.9 KiB
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Strict Level 1//EN">
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<HTML>
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<HEAD>
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<TITLE>Link Reliability - Why URNs are Not the Answer</TITLE>
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</HEAD>
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<BODY BGCOLOR="#ffffff" TEXT="#000000">
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<P>
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<A HREF="../"><IMG BORDER="0" SRC="../Icons/WWW/w3c_home" ALT="W3C" WIDTH="72" HEIGHT="48"
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BORDER="0"></A>
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<A HREF="./"><IMG BORDER="0" SRC="../Icons/WWW/propagation_48x48" ALT="Propagation"
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WIDTH="48" HEIGHT="48" BORDER="0"></A>
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<H1>
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Link Reliability - Why URNs are Not the Answer
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</H1>
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<P>
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We all hate broken links. Some folks have said
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"<A HREF="../Addressing/#URL">URL</A>s are broken. We need
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<A HREF="../Addressing/#URN">URN</A>s. URNs will solve the problem of broken
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links." I doubt it.
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<P>
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URNs will play an important role in publishing on the web (along with copyright
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enforcement mechanisms, payment mechanisms, etc. see
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<A href="../Addressing/citations#URN">URLs as catalog numbers</A>) but I
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doubt they will increase <A HREF="../Glossary#reliability">reliability</A>
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(or quality of service) for the vast majority of web links, because URNs
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will impose administrative overhead (e.g. registration, digital signatures),
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or at least work-flow restrictions (e.g. once you've made a document available
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under a URN, you can never change it). (see
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<A HREF="../Addressing/#STANF">[STANF] </A>for an excellent discussion)
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<P>
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I suspect there are propogation techniques that will increase reliability
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without the cost of human intervention. There are ways to distribute replicas
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of <A HREF="../Glossary#resources">resources</A> such that
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<A HREF="../Glossary#availability">availability </A>will be sufficiently
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high and latency sufficiently low.
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<p>Another mechanism to increase reliability is <a
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href="../Addressing/auto-update">automated link maintenance</a> for
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referential integrity.
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<H2>
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Defining Link Reliability
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</H2>
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<P>
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If we look at link traversal as a case of the
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<A HREF="../Glossary#I-R">information retrieval problem</A>, we can start
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to measure reliability only after we've defined "success."
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<P>
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Successful link traversal generally means finding a resource with perfect
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<A HREF="../Glossary#precision">precision</A> and
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<A HREF="../Glossary#recall">recall</A>, and retrieving an
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<A HREF="../Glossary#authentic">authentic</A> representation of the resource
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in a timely fashion, i.e. with sufficiently low
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<A HREF="../Glossary#latency">latency</A>.
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<P>
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If a resource is <A HREF="../Glossary#replica">replicated </A>to increase
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availability or decrease bandwidth consumption, it is important that the
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various replicas are in sync (or close -- some applications may be willing
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to accept out of date information some small percentage of the time.)
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<P>
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@@Replication mechanisms are complicated by the need to support access control
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and tracking policies.
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<H2>
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More Information
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</H2>
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<DL>
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<DT>
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<A HREF=http://www.w3.org/team/WWW/Addressing/citations.html>Catalog
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Searching</A>
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<DD>
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for info on resource description and discovery, seen as a knowledge
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representation and query problem
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<DT>
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<A HREF="http://www.w3.org/hypertext/WWW/Addressing/Addressing.html">Addressing
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and names</A>
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<DD>
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Tim BL's original design notes
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<DT>
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<A HREF=http://www.w3.org/team/WWW/People/Connolly/drafts/formalism.html>A
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Formalism for Internet Information References</A>
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<DD>
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out-of-date draft
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<DT>
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<A HREF=http://www.w3.org/team/WWW/People/Connolly/drafts/link-rpc.html>Toward
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Reliable, Interoperable Links</A>
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<DD>
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out-of-date draft
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<DT>
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<A HREF="../Addressing/url_test/">URI test suite</A>
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<DD>
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March 16, 1994: The expanded release of a URI test suite (including a fairly
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complete grammar for URI's that includes ways to represent URLs and URIs)
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</DL>
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<P>
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<HR>
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<ADDRESS>
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<A HREF="../People/Connolly/">Connolly</A><BR>
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@(#) $Id: reliable-links.html,v 1.7 1997/08/09 17:55:05 fillault Exp $
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</ADDRESS>
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</BODY></HTML>
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