Re: [Semediawiki-user] Document trace.

[S P. <in...@sk...>]

Peter Simpsons wrote:

> ==================
> Background information:
> ==================
>  
> If there are PAGE A, B, C and D. They have one common "relationship", 
> which is "child of".
> For example,
> Page D: [[Child of: Page C]]
> Page C: [[Child of: Page B]]
> Page B: [[Child of: Page A]]
> Page A: [[Child of: ]]

(You need double-colon :: in the annotations.)

> PS: assuming the user only assigns one parent to one page.
>  
> When the users are viewing Page D, I would to show the following 
> information:
>  
> Page A> PageB> PageC> Page D

Do you know about MediaWiki's special handling of subpages, pages with 
"/" in the title?  See http://www.mediawiki.org/wiki/Subpages.  If you 
enable this feature and create a page named "Page A/Page B/Page C/Page 
D", it will display a little
   < Page A | Page B | Page C
breadcrumb under its title.  I think there are ways in MediaWiki to 
display alternate page headings and/or hide the actual page title.

SMW cannot query for such "meta properties" of MediaWiki pages, so if 
you still wanted a [[Child of:]] relation you'd have to add it and keep 
it in sync with the page title.  You could develop a utility script to 
do this.


> ==================
> My Question:
> ==================
> Is there such extension already?

There are extensions that try to do this for categories.  I think 
http://www.mediawiki.org/wiki/Extension:CategoryBreadcrumb does this. 
http://www.mediawiki.org/wiki/Extension:CategoryTree displays the whole 
tree, maybe it can be configured to just show parents.  But I don't 
think either will help you unless you're willing to make your pages into 
categories.


With current SMW, what you're asking for is a repeating query, in 
pseudo-language it's something like:
   Get the object of this page's "PropertyX", and continue on to ask for 
the object of that page's "PropertyX".  Repeat until some depth limit.

with the added wrinkle that you want to display the results in reverse 
order.

You definitely can't express this with current semantic search (see 
http://ontoworld.org/wiki/Help:Semantic_search).

If you're willing to be explicit, you should be able to issue a query 
for each hierarchy level using SMW's nested query feature  However, I 
found it didn't work on ontoworld.org's pre-release SMW version.  See my 
attempts at http://ontoworld.org/wiki/Drew_Barrymore

The first level is easy, you want to show the current page's Child of 
relations.
   <ask>[[{{PAGENAME}}]] [[Child of::*]]</ask>
which displays Page C.

The next level should be to ask for the object of the "Child of" 
relation for the set of pages from the previous query.  You might hope 
that a nested query will do that:
   <ask format="table"><q>[[{{PAGENAME}}]] [[Child of::*]]</q>[[Child 
of::*]]</ask>

but it doesn't work.  I'm not sure if it should work: I think the nested 
query is still selecting Page D, even though it's been configured to 
display a property that appears as "Page C".  Maybe I'm missing something.

Using a nested query to get the *objects* of a query works fine.  So if 
you annotate with the inverse "Parent of" property, thus e.g. Page C has 
[[Parent of::Page D]], then you can issue queries like:
   <ask>[[parent of::<q>[[parent of::<q>[[{{PAGENAME}}]]</q>]] </q>]] </ask>


> If not, where is the proper location or 
> point I should try to make this work?

Are you asking where in code?  Dive in to SMW_InlineQueries.php.  Try to 
figure out a syntax for "iterate this query on its results" at the same 
time as you develop the query code.  Maybe SQL extensions and SPARQL 
variants have good ideas.

> Any suggestion?

--
=S Page