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From "Sami Siren (JIRA)" <>
Subject [jira] Commented: (NUTCH-766) Tika parser
Date Fri, 22 Jan 2010 11:35:21 GMT


Sami Siren commented on NUTCH-766:

> Sure, but it would be silly to block the whole Tika plugin because Tika does not support
such or such format as well as the original Nutch plugins. As I explained above we can configure
which parser to use for which mimetype and use the Tika-plugin by default. Hopefully the Tika
implementation will get better and better and there will be no need for keeping the old plugins.

I meant test files for the parsers we replace, not all

> BTW lists the differences between the current
version of Tika and the existing Nutch parsers

ok, I had misses that one. 

> Tika parser
> -----------
>                 Key: NUTCH-766
>                 URL:
>             Project: Nutch
>          Issue Type: New Feature
>            Reporter: Julien Nioche
>            Assignee: Chris A. Mattmann
>             Fix For: 1.1
>         Attachments: Nutch-766.ParserFactory.patch, NUTCH-766.tika.patch
> Tika handles a lot of different formats under the bonnet and exposes them nicely via
SAX events. What is described here is a tika-parser plugin which delegates the pasring mechanism
of Tika but can still coexist with the existing parsing plugins which is useful for formats
partially handled by Tika (or not at all). Some of the elements below have already been discussed
on the mailing lists. Note that this is work in progress, your feedback is welcome.
> Tika is already used by Nutch for its MimeType implementations. Tika comes as different
jar files (core and parsers), in the work described here we decided to put the libs in 2 different
> NUTCH_HOME/lib : tika-core.jar
> NUTCH_HOME/tika-plugin/lib : tika-parsers.jar
> Tika being used by the core only for its Mimetype functionalities we only need to put
tika-core at the main lib level whereas the tika plugin obviously needs the tika-parsers.jar
+ all the jars used internally by Tika
> Due to limitations in the way Tika loads its classes, we had to duplicate the TikaConfig
class in the tika-plugin. This might be fixed in the future in Tika itself or avoided by refactoring
the mimetype part of Nutch using extension points.
> Unlike most other parsers, Tika handles more than one Mime-type which is why we are using
"*" as its mimetype value in the plugin descriptor and have modified so
that it considers the tika parser as potentially suitable for all mime-types. In practice
this means that the associations between a mime type and a parser plugin as defined in parse-plugins.xml
are useful only for the cases where we want to handle a mime type with a different parser
than Tika. 
> The general approach I chose was to convert the SAX events returned by the Tika parsers
into DOM objects and reuse the utilities that come with the current HTML parser i.e. link
detection,  metatag handling but also means that we can use the HTMLParseFilters in exactly
the same way. The main difference though is that HTMLParseFilters are not limited to HTML
documents anymore as the XHTML tags returned by Tika can correspond to a different format
for the original document. There is a duplication of code with the html-plugin which will
be resolved by either a) getting rid of the html-plugin altogether or b) exporting its jar
and make the tika parser depend on it.
> The following libraries are required in the lib/ directory of the tika-parser : 
>       <library name="asm-3.1.jar"/>
>       <library name="bcmail-jdk15-144.jar"/>
>       <library name="commons-compress-1.0.jar"/>
>       <library name="commons-logging-1.1.1.jar"/>
>       <library name="dom4j-1.6.1.jar"/>
>       <library name="fontbox-0.8.0-incubator.jar"/>
>       <library name="geronimo-stax-api_1.0_spec-1.0.1.jar"/>
>       <library name="hamcrest-core-1.1.jar"/>
>       <library name="jce-jdk13-144.jar"/>
>       <library name="jempbox-0.8.0-incubator.jar"/>
>       <library name="metadata-extractor-2.4.0-beta-1.jar"/>
>       <library name="mockito-core-1.7.jar"/>
>       <library name="objenesis-1.0.jar"/>
>       <library name="ooxml-schemas-1.0.jar"/>
>       <library name="pdfbox-0.8.0-incubating.jar"/>
>       <library name="poi-3.5-FINAL.jar"/>
>       <library name="poi-ooxml-3.5-FINAL.jar"/>
>       <library name="poi-scratchpad-3.5-FINAL.jar"/>
>       <library name="tagsoup-1.2.jar"/>
>       <library name="tika-parsers-0.5-SNAPSHOT.jar"/>
>       <library name="xml-apis-1.0.b2.jar"/>
>       <library name="xmlbeans-2.3.0.jar"/>
> There is a small test suite which needs to be improved. We will need to have a look at
each individual format and check that it is covered by Tika and if so to the same extent;
the Wiki is probably the right place for this. The language identifier (which is a HTMLParseFilter)
seemed to work fine.
> Again, your comments are welcome. Please bear in mind that this is just a first step.

> Julien

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