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101 lines
4.4 KiB
101 lines
4.4 KiB
<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content=
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"HTML Tidy for Mac OS X (vers 31 October 2006 - Apple Inc. build 13), see www.w3.org" />
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<title>
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Naming -- /DesignIssues
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</title>
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<nextid n="z2" />
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</head>
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<body bgcolor="#FFC060" text="#302005">
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<a href="OldDocs.html"><img src=
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"../Icons/WWW/arch1990" /></a>TimBL
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<hr />
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<h1>
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Document Naming
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</h1>This is probably the most crucial aspect of design and
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standardization in an open hypertext system. It concerns the
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syntax of a name by which a document or part of a document (an
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anchor) is referenced from anywhere else in the world.
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<p>
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As many protocols are currently used for information
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retrieval, the address must be capable of encompassing many
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protocols, access methods or, indeed, naming schemes.
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</p>
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<p>
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The <a name="1" href="../Addressing/Addressing.html">WWW
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scheme</a> uses a prefix to give the addressing sub-scheme,
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and then a syntax dependent on the prefix used, in order to
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be open to any new naming systems.
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</p>
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<h2>
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Name or Address, or Identifier?
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</h2>Conventionally, a "name" has tended to mean a logical way
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of referring to an object in some abstract name space, while
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the term "address" has been used for something which specifies
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the physical location. The term "unique identifier" generally
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referred to a name which was guaranteed to be unique but had
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little significance as regards the logical name or physical
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address. A name server was used to convert names or unique
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identifiers into addresses.
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<p>
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With wide-area distributed systems, this distinction blurs.
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Locally, things which at first look like physical addresses
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develop more and more levels of translation, so that they
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cease to give the actual location of the object. At the same
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time, a logical name or a unique identifier must contain some
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information which allows the name server to know where to
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start looking. In a global context, for example
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"1237159242346244234232342342423468762342368" might well be
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unique, but it contains insufficient (apparent) structure for
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a name server to look it up. The name "info.cern.ch" has a
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structure which allows a search to be made in several stages.
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In fact, practical systems using unique identifiers generally
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hide within them some clues for the name server, such as a
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node name.
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</p>
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<p>
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A hypertext link to a document ought to be specified using
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the most logical name as opposed to a physical address. This
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is (almost) the only way of getting over the problem of
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documents being physically moved. As the naming scheme
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becomes more abstract, resolving the name becomes less of a
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simple look-up and more of a search.
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</p>
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<p>
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One expects in practice the translation of a document name
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taking several stages as the name becomes less abstract and
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more physical.
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</p>
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<h2>
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Hints
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</h2>Some document reference formats contain "hints" to the
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reader about the document, such as server availability,
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copyright status, last known physical address and data formats.
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It is very important not to confuse these with the document's
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name, as they have a shorter lifetime than the document.
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<h2>
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X500
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</h2>The X500 directory service protocol defines an abstract
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name space which is hierarchical. It allows objects such as
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organizations, people, and documents to be arranged in a tree.
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Whereas the hierarchical structure might make it difficult to
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decide in which of two locations to put an object (it's not
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hypertext), this does allow a unique name to be given for
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anything in the tree. X500 functionally seems to meet the needs
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of the logical name space in a wide-area hypertext system.
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Implementations are somewhat rare at the moment of writing, so
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it cannot be assumed as a general infrastructure.
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<p>
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If this direction is chosen for naming, it still leaves open
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the question of the format of the address into which a
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document name will be translated. This must also be left as
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open-ended as the set of protocols.
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</p>
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<address>
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<a name="0" href=
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"http://www.w3.org./hypertext/TBL_Disclaimer.html">Tim BL
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1991</a>
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</address>
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</body>
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</html>
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