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From "Andrzej Bialecki (JIRA)" <j...@apache.org>
Subject [jira] Commented: (NUTCH-139) Standard metadata property names in the ParseData metadata
Date Fri, 20 Jan 2006 12:11:42 GMT
    [ http://issues.apache.org/jira/browse/NUTCH-139?page=comments#action_12363394 ] 

Andrzej Bialecki  commented on NUTCH-139:
-----------------------------------------

Yes, I agree with the split into a generic MetaData container, and subclasses that define
necessary constants for metadata names.

However, your proposal still doesn't address the key issue of having a set of "approved" or
"final" values for metadata.

Example: in index-basic you need to index the title. It's not in the ContentProperties (wrong
level) but in ParseProperties. A content parser may discover that the original title is empty
or invalid. Still, this original value should be stored, under the standard key "dc:title".
But then the parser knows the best what to do with an invalid value (is the ultimate authority),
and it knows that the rest of Nutch really needs a meaningful value for the title, so it constructs
it from the first line of the body text. However, with your porposed approach the parser cannot
put it under the same key in ParseProperties (dc:title), because either it overwrites the
original value, or it turns it into a simple multi-value property - as if the original metadata
had multiple values.

That's why we insisted that the parser needs to use an "X-nutch-dc:title", so that it has
a way to mark the final value that will remain in force for further processing. If you have
a better way to achieve the same semantics, please explain.

> Standard metadata property names in the ParseData metadata
> ----------------------------------------------------------
>
>          Key: NUTCH-139
>          URL: http://issues.apache.org/jira/browse/NUTCH-139
>      Project: Nutch
>         Type: Improvement
>   Components: fetcher
>     Versions: 0.7.1, 0.7, 0.6, 0.7.2-dev, 0.8-dev
>  Environment: Power Mac OS X 10.4, Dual Processor G5 2.0 Ghz, 1.5 GB  RAM, although bug
is independent of environment
>     Reporter: Chris A. Mattmann
>     Assignee: Chris A. Mattmann
>     Priority: Minor
>      Fix For: 0.7.2-dev, 0.8-dev, 0.7.1, 0.7, 0.6
>  Attachments: NUTCH-139.060105.patch, NUTCH-139.Mattmann.patch.txt, NUTCH-139.jc.review.patch.txt
>
> Currently, people are free to name their string-based properties anything that they want,
such as having names of "Content-type", "content-TyPe", "CONTENT_TYPE" all having the same
meaning. Stefan G. I believe proposed a solution in which all property names be converted
to lower case, but in essence this really only fixes half the problem right (the case of identifying
that "CONTENT_TYPE"
> and "conTeNT_TyPE" and all the permutations are really the same). What about
> if I named it "Content     Type", or "ContentType"?
>  I propose that a way to correct this would be to create a standard set of named Strings
in the ParseData class that the protocol framework and the parsing framework could use to
identify common properties such as "Content-type", "Creator", "Language", etc.
>  The properties would be defined at the top of the ParseData class, something like:
>  public class ParseData{
>    .....
>     public static final String CONTENT_TYPE = "content-type";
>     public static final String CREATOR = "creator";
>    ....
> }
> In this fashion, users could at least know what the name of the standard properties that
they can obtain from the ParseData are, for example by making a call to ParseData.getMetadata().get(ParseData.CONTENT_TYPE)
to get the content type or a call to ParseData.getMetadata().set(ParseData.CONTENT_TYPE, "text/xml");
Of course, this wouldn't preclude users from doing what they are currently doing, it would
just provide a standard method of obtaining some of the more common, critical metadata without
pouring over the code base to figure out what they are named.
> I'll contribute a patch near the end of the this week, or beg. of next week that addresses
this issue.

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