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From "Giuseppe Totaro (JIRA)" <j...@apache.org>
Subject [jira] [Created] (TIKA-1691) Apache Tika for enabling metadata interoperability
Date Tue, 21 Jul 2015 17:08:04 GMT
Giuseppe Totaro created TIKA-1691:
-------------------------------------

             Summary: Apache Tika for enabling metadata interoperability
                 Key: TIKA-1691
                 URL: https://issues.apache.org/jira/browse/TIKA-1691
             Project: Tika
          Issue Type: New Feature
            Reporter: Giuseppe Totaro
            Assignee: Giuseppe Totaro


If am not wrong, enabling consistent metadata across file formats is already (partially) provided
into Tika by relying on {{TikaCoreProperties}} and, within the context of Solr, {{ExtractingRequestHandler}}
(by defining how to map metadata fields in {{solrconfig.xml}}). However, I am working on a
new component for both schema mapping (to operate on the name of metadata properties) and
instance transformation (to operate on the value of metadata) that consists, essentially,
of the following changes:

* A wrapper of {{Metadata}} object ({{MappedMetadata.java}}) that decorates the {{set}} method
(currently, line number 367 of {{Metadata.java}}) by applying the given mapping functions
(via configuration) before setting metadata properties.
* Basic mapping functions ({{BasicMappingUtils.java}}) that are utility methods to map a set
of metadata to the target schema.
* A new {{MetadataConfig}} object that, as well as {{TikaConfig}}, may be configured via XML
file (organized as showed in the following snippet) and allows to perform a fine-grained metadata
mapping by using Java reflection.

{code:xml|title=tika-metadata.xml|borderStyle=solid}
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<properties>
  <mappings>
    <mapping type="type/sub-type">
      <relation name="SOURCE_FIELD">
        <target>TARGET_FIELD</target>
        <expression>exclude|include|equivalent|overlap</expression>
        <function name="FUNCTION_NAME">
          <argument>ARGUMENT_VALUE</argument>
        </function>
        <cardinality>
          <source>SOURCE_CARDINALITY</source>
          <target>TARGET_CARDINALITY</target>
          <order>ORDER_NUMBER</order>
          <dependencies>
            <field>FIELD_NAME</field>
          </dependencies>
        </cardinality>
      </relation>
    </mapping>
    ...
    <mapping> <!-- This contains the fallback strategy for unknown metadata -->
      <relation>
        ...
      </relation>
    <mapping>
  </mappings>
</properties>
{code}

The theoretical definition of metadata mapping is available in "[A survey of techniques for
achieving metadata interoperability|http://www.researchgate.net/profile/Bernhard_Haslhofer/publication/220566013_A_survey_of_techniques_for_achieving_metadata_interoperability/links/02e7e533e76187c0b8000000.pdf]".
This paper shows also some basic examples of metadata mappings.

Currently, I am still working on some core functionalities, but I have already performed some
experiments by using a small prototype.

By the way, I think that we should modify the method {{add}} in order to use {{set}} instead
of {{metadata.put}} (currently, line number 316 of {{Metadata.java}}). This is a trivial change
(I could create a new Jira issue about that), but it would allow to be coherent with the other
implementation of {{add}} method and, moreover, the methods of {{Metadata}} could be extended
more easily.

I would really appreciate your feedback about this proposal. If you believe that it is a good
idea, I could provide the code in few days.

Thanks a lot,
Giuseppe



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