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<?xml version="1.0" encoding="UTF-8"?>
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<document>
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<properties>
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<title>Plan for enhancements to Lucene</title>
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<authors>
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<person email="acoliver@apache.org" name="Andrew C. Oliver" id="AO"/>
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</authors>
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</properties>
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<body>
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<section name="Purpose">
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<p>
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The purpose of this document is to outline plans for
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making <a href="http://jakarta.apache.org/lucene">
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Apache Lucene</a> work as a more general drop-in
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component. It makes the assumption that this is an
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objective for the Lucene user and development community.
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</p>
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<p>
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The best reference is <a href="http://www.htdig.org">
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htDig</a>, though it is not quite as sophisticated as
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Lucene, it has a number of features that make it
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desirable. It however is a traditional c-compiled app
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which makes it somewhat unpleasant to install on some
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platforms (like Solaris!).
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</p>
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<p>
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This plan is being submitted to the Lucene developer
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community for an initial reaction, advice, feedback and
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consent. Following this it will be submitted to the
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Lucene user community for support. Although, I'm (Andy
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Oliver) capable of providing these enhancements by
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myself, I'd of course prefer to work on them in concert
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with others.
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</p>
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<p>
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While I'm outlaying a fairly large feature set, these can
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be implemented incrementally of course (and are probably
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best if done that way).
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</p>
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</section>
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<section name="Goal and Objectives">
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<p>
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The goal is to provide features to Lucene that allow it
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to be used as a drop-in search engine. It should provide
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many of the features of projects like <a
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href="http://www.htdig.org">htDig</a> while surpassing
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them with unique Lucene features and capabilities such as
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easy installation on and java-supporting platform,
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and support for document fields and field searches. And
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of course, <a href="http://apache.org/LICENSE">
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a pragmatic software license</a>.
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</p>
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<p>
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To reach this goal we'll implement code to support the
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following objectives that augment but do not replace
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the current Lucene feature set.
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</p>
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<ul>
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<li>
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Document Location Independence - meaning mapping
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real contexts to runtime contexts.
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Essentially, if the document is at
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/var/www/htdocs/mydoc.html, I probably want it
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indexed as
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http://www.bigevilmegacorp.com/mydoc.html.
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</li>
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<li>
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Standard methods of creating central indicies -
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file system indexing is probably less useful in
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many environments than is *remote* indexing (for
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instance http). I would suggest that most folks
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would prefer that general functionality be
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supported by Lucene instead of having to write
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code for every indexing project. Obviously, if
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what they are doing is *special* they'll have to
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code, but general document indexing across
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web servers would not qualify.
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</li>
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<li>
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Document interpretation abstraction - currently
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one must handle document object construction via
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custom code. A standard interface for plugging
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in format handlers should be supported.
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</li>
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<li>
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Mime and file-extension to document
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interpretation mapping.
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</li>
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</ul>
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</section>
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<section name="Crawlers">
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<p>
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Crawlers are data source executable code. They crawl a file
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system, ftp site, web site, etc. to create the index.
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These standard crawlers may not make ALL of Lucene's
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functionality available, though they should be able to
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make most of it available through configuration.
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</p>
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<!--<section name="AbstractIndexer">-->
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<p>
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<b> Abstract Crawler </b>
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</p>
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<p>
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The AbstractCrawler is basically the parent for all
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Crawler classes. It provides implementation for the
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following functions/properties:
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</p>
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<ul>
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<li>
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index path - where to write the index.
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</li>
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<li>
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cui - create or update the index
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</li>
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<li>
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root context - the start of the pathname
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that should be replaced by the
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replace with property or dropped
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entirely. Example: /opt/tomcat/webapps
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</li>
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<li>
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replace with - when specified replaces
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the root context. Example:
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http://jakarta.apache.org.
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</li>
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<li>
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replacement type - the type of
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replace with path: relative, URL or
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path.
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</li>
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<li>
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location - the location to start
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indexing at.
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</li>
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<li>
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doctypes - only index documents with
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these doctypes. If not specified all
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registered mime-types are used.
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Example: "xml,doc,html"
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</li>
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<li>
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recursive - if not specified is turned
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off.
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</li>
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<li>
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level - optional level of directory or
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links to traverse. By default is
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assumed to be infinite. Recursive must
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be turned on or this is ignored. Range:
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0 - Long.MAX_VALUE.
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</li>
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<li>
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SleeptimeBetweenCalls - can be used to
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avoid flooding a machine with too many
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requests
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</li>
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<li>
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RequestTimeout - kill the crawler
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request after the specified period of
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inactivity.
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</li>
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<li>
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IncludeFilter - include only items
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matching filter. (can occur multiple
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times)
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</li>
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<li>
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ExcludeFilter - exclude only items
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matching filter. (can occur multiple
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times)
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</li>
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<li>
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ExpandOnly - use but do not index items
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that match this pattern (regex?) (can
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occur multiple times)
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</li>
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<li>
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NoExpand - Index but do not follow the
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links in items that match this pattern
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(regex?) (can occur multiple times)
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</li>
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<li>
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MaxItems - stops indexing after x
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documents have been indexed.
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</li>
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<li>
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MaxMegs - stops indexing after x megs
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have been indexed.. (should this be in
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specific crawlers?)
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</li>
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<li>
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properties - in addition to the settings
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(probably from the command line) read
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this properties file and get them from
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it. Command line options override
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the properties file in the case of
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duplicates. There should also be an
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environment variable or VM parameter to
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set this.
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</li>
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</ul>
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<!--</section>-->
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<!--<s2 title="FileSystemIndexer">-->
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<p>
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<b>FileSystemCrawler</b>
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</p>
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<p>
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This should extend the AbstractCrawler and
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support any additional options required for a
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file system index.
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</p>
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<!--</s2>-->
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<!--<s2 title="HTTPIndexer">-->
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<p>
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<b>HTTP Crawler </b>
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</p>
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<p>
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Supports the AbstractCrawler options as well as:
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</p>
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<ul>
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<li>
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span hosts - Whether to span hosts or not,
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by default this should be no.
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</li>
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<li>
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restrict domains - (ignored if span
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hosts is not enabled). Whether all
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spanned hosts must be in the same domain
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(default is off).
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</li>
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<li>
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try directories - Whether to attempt
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directory listings or not (so if you
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recurse and go to
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/nextcontext/index.html this option says
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to also try /nextcontext to get the dir
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listing)
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</li>
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<li>
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map extensions -
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(always/default/never/fallback). Whether
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to always use extension mapping, by
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default (fallback to mime type), NEVER
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or fallback if mime is not available
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(default).
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</li>
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<li>
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ignore robots - ignore robots.txt, on or
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off (default - off)
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</li>
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</ul>
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<!-- </s2> -->
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</section>
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<section name="MIMEMap">
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<p>
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A configurable registry of document types, their
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description, an identifier, mime-type and file
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extension. This should map both MIME -> factory
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and extension -> factory.
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</p>
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<p>
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This might be configured at compile time or by a
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properties file, etc. For example:
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</p>
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<table>
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<tr>
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<td>Description</td>
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<td>Identifier</td>
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<td>Extensions</td>
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<td>MimeType</td>
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<td>DocumentFactory</td>
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</tr>
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<tr>
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<td>"Word Document"</td>
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<td>"doc"</td>
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<td>"doc"</td>
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<td>"vnd.application/ms-word"</td>
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<td>POIWordDocumentFactory</td>
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</tr>
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<tr>
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<td>"HTML Document"</td>
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<td>"html"</td>
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<td>"html,htm"</td>
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<td></td>
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<td>HTMLDocumentFactory</td>
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</tr>
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</table>
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</section>
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<section name="DocumentFactory">
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<p>
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An interface for classes which create document objects
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for particular file types. Examples:
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HTMLDocumentFactory, DOCDocumentFactory,
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XLSDocumentFactory, XML DocumentFactory.
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</p>
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</section>
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<section name="FieldMapping classes">
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<p>
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A class that maps standard fields from the
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2002-02-23 17:02:55 -05:00
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DocumentFactories into *fields* in the Document objects
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they create. I suggest that a regular expression system
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or xpath might be the most universal way to do this.
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For instance if perhaps I had an XML factory that
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represented XML elements as fields, I could map content
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from particular fields to their fields or suppress them
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entirely. We could even make this configurable.
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</p>
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<p>
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2002-06-04 11:29:32 -04:00
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2002-02-23 17:02:55 -05:00
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for example:
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</p>
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<ul>
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<li>
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htmldoc.properties
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</li>
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<li>
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suppress=*
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</li>
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<li>
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author=content:g/author\:\ ........................................./
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</li>
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<li>
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author.suppress=false
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</li>
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<li>
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title=content:g/title\:\ ........................................./
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</li>
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<li>
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title.suppress=false
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</li>
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</ul>
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<p>
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In this example we map html documents such that all
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fields are suppressed but author and title. We map
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author and title to anything in the content matching
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author: (and x characters). Okay my regular expresions
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2002-02-23 17:02:55 -05:00
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suck but hopefully you get the idea.
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</p>
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</section>
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<section name="Final Thoughts">
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<p>
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2002-06-04 11:29:32 -04:00
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We might also consider eliminating the DocumentFactory
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entirely by making an AbstractDocument from which the
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current document object would inherit from. I
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experimented with this locally, and it was a relatively
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minor code change and there was of course no difference
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in performance. The Document Factory classes would
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instead be instances of various subclasses of
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AbstractDocument.
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</p>
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<p>
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2002-06-04 11:29:32 -04:00
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My inspiration for this is HTDig (http://www.htdig.org/).
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While this goes slightly beyond what HTDig provides by
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providing field mapping (where HTDIG is just interested
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in Strings/numbers wherever they are found), it provides
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at least what I would need to use this as a drop-in for
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most places I contract at (with the obvious exception of
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a default set of content handlers which would of course
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develop naturally over time).
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</p>
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<p>
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2002-06-04 11:29:32 -04:00
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I am able to certainly contribute to this effort if the
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development community is open to it. I'd suggest we do
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it iteratively in stages and not aim for all of this at
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once (for instance leave out the field mapping at first).
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</p>
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<p>
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2002-06-04 11:29:32 -04:00
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Anyhow, please give me some feedback, counter
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suggestions, let me know if I'm way off base or out of
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2002-02-23 17:02:55 -05:00
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line, etc. -Andy
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</p>
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</section>
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2002-06-04 11:29:32 -04:00
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2002-02-23 17:02:55 -05:00
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</body>
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</document>
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