Hey all,
I have implemented general support for value distributions in result
formats in SMW. This email explains this feature and is meant to gather
feedback on it before SMW 1.7 is released.
== Goal ==
Allow visualizing how many times each value in a result occurs, ie allow
for creating value distributions.
For example, this result set: foo bar baz foo bar bar ohi
Will be turned into
* bar (3)
* foo (2)
* baz (1)
* ohi (1)
This can then be displayed in chart formats, with the value as label and
the occurrence count as value. Although the most obvious use for this are
charts, it can really be used with any format.
== Current implementation: how to use it ==
Each format needs to add support for this functionality before you'll be
able to use it to visualize value distributions. Right now only jqplotbar
and jqplotpie make use of it. All formats that support this functionality
accept 3 additional parameters:
* distribution (on/off) - if a value distribution should be calculated and
shown instead of the regular results.
* distributionsort (asc/desc/none) - the sort of the values, by occurance
count.
* distributionlimit (positive whole number) - the max amount of values to
visualize.
This example will get the countries the matching cities are located in,
count the occurance of each, and display this as a pie chart. Note the use
of the mainlabel parameter. If this is not done, the cities themselves will
also be put into the value distribution.
{{#ask: [[Category:Locations]] [[Has location type::City]]
| ?Located in
| format=jqplotpie
| distribution=on
| mainlabel=-
| limit=500
}}
This example will do the same query, but will only show the 10 countries
with most matching cities, in descending order.
{{#ask: [[Category:Locations]] [[Has location type::City]]
| ?Located in
| format=jqplotpie
| distribution=on
| distributionsort=desc
| distributionlimit=10
| mainlabel=-
| limit=500
}}
You can see these examples and 2 others working on the mapping
documentation wiki, making use of the example semantic data there:
http://mapping.referata.com/wiki/Value_distribution_examples
== Implementation details (technical) ==
After looking into several options I decided to implement this as a result
printer class deriving from SMWResultPrinter, requiring changes to each
format that wants to support this behaviour, but making this relatively
easy. This approach seems like a good balance between making this
functionality available as easy as possible and staying sane.
This class is called SMWDistributablePrinter and can be found here:
http://svn.wikimedia.org/viewvc/mediawiki/trunk/extensions/SemanticMediaWiki/includes/queryprinters/SMW_QP_Distributable.php?view=markup
Example jqplotpie implementation:
http://svn.wikimedia.org/viewvc/mediawiki/trunk/extensions/SemanticResultFormats/jqPlot/SRF_jqPlotPie.php?view=markup
== Request for comments ==
Feedback is welcome. The main question for users is what names the
parameters should use. Right now they all start with "distribution", but
there might be a better (and shorter) name. From developers I'd like to
know if you agree with this architecture.
Cheers
--
Jeroen De Dauw
http://www.bn2vs.com
Don't panic. Don't be evil.
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