Semantic MediaWiki: Is it possible to use subqueries rather than properties for tables?

Question

I'm still trying to make my wiki more "dynamic" in order to get rid of duplicated data. In my previous question I was asking how I could bind multiple pages and retrieve properties through bound pages. Since that question is already resolved for simple cases (however I don't like my solution there much), I would like to make it work for tables. let's consider the same page and property structure I mentioned in my question again, thus the following code

{{#ask: [[Category:Venues]] [[Self name::Heineken Music Hall]]}}
{{#ask: [[Category:Cities]] [[-Ref city.Self name::Heineken Music Hall]]}}
{{#ask: [[Category:Countries]] [[-Ref country.-Ref city.Self name::Heineken Music Hall]]}}

retrieves the venue, city (Amsterdam) and country (Netherlands) using inline queries. However I'm not sure if such an approach is possible for tables. As far as I know, #ask can generate a table generating columns out of direct properties :

{{#ask: [[Category:Live events]]
| ?Self date = Date
| ?Ref venue = Venue
| mainlabel = -
}}

Output:

+-----------------+---------------------+
| Date            | Venue               |
+-----------------+---------------------+
| 3 December 2012 | Heineken Music Hall |
+-----------------+---------------------+

I would also like to add the City and Country columns. The problem is, as I mentioned above, the city and country properties are not put directly into the Venue page so the #ask function might use inline subqueries. But I can't make it work:

{{#ask: [[Category:Live events]]
| ?Self date = Date
| ?Ref venue = Venue
| ?WHAT_EXPRESSION_HERE? = City
| ?EVEN_MORE_COMPLEX_EXPRESSION_HERE? = Country
| mainlabel = -
}}

The first thing I'm thinking about is using templates using the format = template and template = TEMPLATE_NAME. I managed to extract the bound city using this approach by creating the required template and parsing {{{1}}}... parameters, but I cannot seem to extract country (simple to extract: date, venue; complex: city; not able: country). Also using the templates approach seems to be fragile and not very consistent to me.

Is it possible to specify subqueries/expressions rather than properties for tables to extract properties from indirectly bound pages in Semantic MediaWiki (probably never using templates)?

Lyubomyr Shaydariv · Accepted Answer · 2016-03-10T22:44:05.627

As far as I understand, this is not possible in Semantic MediaWiki directly, however it can be worked around. In short, the template format is required, and here it is:

{{#ask: [[Category:Live events]]
| ?Self date = Date
| ?Ref venue = Venue
| mainlabel = -
| format = template
| template = Row:Live events table
| named args = yes
}}

The Template:Row:Live events table template is as follows:

<includeonly><!--
-->{{#vardefine: DATE | {{{?Date}}}}}<!--
-->{{#vardefine: VENUE | {{{?Venue}}}}}<!--
-->{{#vardefine: CITY | {{SHOW_REF|{{#var: VENUE}}|?Ref city}}}}<!--
-->{{#vardefine: COUNTRY | {{SHOW_REF|{{#var: CITY}}|?Ref country}}}}<!--
-->{{#vardefine: CONTINENT | {{SHOW_REF|{{#var: COUNTRY}}|?Ref continent}}}}<!--
-->{{#var: DATE}}, {{#var: VENUE}}, {{#var: CITY}}, {{#var: COUNTRY}} {{#var: FLAG}}, {{#var: CONTINENT}}<br/><!--
--></includeonly>

In the template above I use named arguments for easiness. However, I use #vardefine and #var to store and retrieve some data from the current row. These functions are supplied by the Extension:Variables extension. Also I use two auxiliary templates: SHOW SELF and SHOW REF to simplify data extraction. The first template, SHOW SELF, is just a shortcut:

<includeonly>{{#show: {{FULLPAGENAME}} | {{{1|}}}}}</includeonly>

to extract a property for the current page. The second template called SHOW REF simplifies data extraction for the given page, not the current one:

<includeonly>{{#show: {{PARSE_SMW_PAGE | {{{1|}}} }} | {{{2|}}}}}</includeonly>

And yes, the PARSE SMW PAGE just strips left and right brackets, and optional leading colon:

<includeonly>{{#explode:
{{#sub: {{{1}}} | {{#ifeq: {{#pos: {{{1}}} | [:}} | 1 | 3 | 2 }} | -2 }}
| {{!}}
}}</includeonly>

#explode and #pos are supplied from Extension:StringFunctions, #ifeq is supplied from Extension:ParserFunctions and {{!}} is a dummy template for the | character.

As you can see, I managed to crawl the following page relationships:

Venue to city
City to country
Country to continent

Hope this helps someone else too.

Semantic MediaWiki: Is it possible to use subqueries rather than properties for tables?

1 Answers1