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From "Andrzej Bialecki (JIRA)" <j...@apache.org>
Subject [jira] Created: (NUTCH-365) Flexible URL normalization
Date Sat, 09 Sep 2006 13:22:22 GMT
Flexible URL normalization
--------------------------

                 Key: NUTCH-365
                 URL: http://issues.apache.org/jira/browse/NUTCH-365
             Project: Nutch
          Issue Type: Improvement
    Affects Versions: 0.9.0
            Reporter: Andrzej Bialecki 
             Fix For: 0.9.0


This patch is a heavily restructured version of the patch in NUTCH-253, so much that I decided
to create a separate issue. It changes the URL normalization from a selectable single class
to a flexible and context-aware chain of normalization filters.

Highlights:

* rename all *UrlNormalizer* to *URLNormalizer* for consistency.

* use a "chained filter" pattern for running several normalizers in sequence

* the order in which normalizers are executed is defined by "urlnormalizer.order" property,
which lists space-separated implementation classes. If there are more normalizers active than
explicitly named on this list, they will be run in random order after the ones specified on
the list are executed.

* define a set of contexts (or scopes) in which normalizers may be called. Each scope can
have its own list of normalizers (via "urlnormalizer.scope.<scope_name>" property) and
its own order (via "urlnormalizer.order.<scope_name>" property). If any of these properties
are missing, default settings are used.

* each normalizer may further select among many configurations, depending on the context in
which it is called, using a modified API:

   URLNormalizer.normalize(String url, String scope);

* if a config for a given scope is not defined, then the default config will be used.

* several standard contexts / scopes have been defined, and various applications have been
modified to attempt using appropriate normalizer in their context.

* all JUnit tests have been modified, and run successfully.

NUTCH-363 suggests to me that further changes may be required in this area, perhaps we should
combine urlfilters and urlnormalizers into a single subsystem of url munging - now that we
have support for scopes and flexible combinations of normalizers we could turn URLFilters
into a special case of normalizers (or vice versa, depending on the point of view) ... 

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