Re: Nested facets revisited

At 11:21 PM 2/20/2005, Marcel wrote:
>Some facets are only relevant in some situations
>We need some type of a conditional facet. Travis came up with the notion
>of a "scope". The scope of a facet would determine whether or not a
>facet is visible.
>http://www.poorbuthappy.com/ease/archives/2004/04/23/1235/nested-facets
>If I go to XFML.org I see there is still no scope defined in XFML. Why?
>Is "scope" not the answer to this problem?

To be obnoxiously vague, it depends on what you need it for. I think 
"scope" is a solution if you are creating navigational data that will be 
browsed by a human or robot user. It enables the use suggested by Peter's 
blog entry and also most of the uses suggested by that entry's comments. 
But if your facet data is meant for consumption in other ways -- massive 
number-crunching, for example, or for descriptive purposes -- then "scope" 
may not be the way to go.

I'll offer this enhancement to the FacetMap 2.0 schema, and you can tell me 
if it works for you. Consider this a starting point, a request for 
comments. I will publish the result in the 2.1 schema.

FacetMap 2.0 <http://facetmap.com/spec/facetmap2_0.dtd> defines the various 
facet types like this:

<!ELEMENT taxonomy (heading+)>
<!ELEMENT spectrum (range*)>
<!ELEMENT facet EMPTY>

such that a taxonomy facet contains taxonomic headings, a spectrum facet 
contains range headings, and a generic facet (used for reference) contains 
nothing. The enhancement would extend the definitions like so:

<!ELEMENT taxonomy (scope?, heading+)>
<!ELEMENT spectrum (scope?, range*)>
<!ELEMENT facet (scope?)>

so that one scope element could optionally be included, defined as follows:

<!ELEMENT scope EMPTY>
<!ATTLIST scope
   facetid ID #REQUIRED
   heading ID #REQUIRED
 >

If present, the <scope> element indicates that the facet is only relevant 
within the context of the heading specified by "heading", and its 
subheadings. The "facetid" attribute indicates which facet that heading 
lives in. (The definition of "relevant" is still fuzzy and perhaps should 
remain fuzzy.) For example:

<taxonomy facetid="product">
   <heading id="electronics">
     <heading id="cameras" />
   </heading>
   <heading id="furnishings">
     <heading id="sofas" />
   </heading>
</taxonomy>

<taxonomy facetid="lens-type">
   <scope facetid="product" heading="cameras" />
   <heading id="zoom" />
   <heading id="fixed" />
</taxonomy>

In this example, the "lens-type" facet is only relevant if the user has 
selected the "cameras" heading in the "product" facet. If that's the case, 
the "lens-type" facet and its headings are available for selection. 
Otherwise (say, if "sofas" is selected instead of "cameras", or if no 
"product" heading is selected at all), the "lens-type" facet is ignored. 
Question: is there a need to combine two or more <scope> elements in a 
single facet?

All feedback is appreciated.

Travis Wilson
Development
http://facetmap.com



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