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Retrieving Information

Overview

How can we view the data we enter?

  • Special:Browse — view all data for a page
  • Property:Name — view all data for property
  • Special:Types — view all properties of some type
  • Special:Properties — view all properties
  • And various others (not quite as important)

Factbox

The Factbox shows all data contained as annotations of one page

  • Below edit field in editing preview
  • At page bottom on some or all pages
  • Can be activated with the __SHOWFACTBOX__ magic word

Special:Browse

The special page Special:Browse shows
… all annotations contained in a page
… other pages’ attributes that link to the selected page

Embedding Data into Wiki Pages

The parser function #show can display property values from other wiki pages

Example

Example 

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{{#show:Berlin|?has population}} – show this number 
{{#show:Germany|?has capital}} – show this page (link)

→ Re-use data without re-entering it

Querying Data

SMW defines its own query language called AQL, which resembles the (semantic) MediaWiki syntax to some extent.

The parser function #ask allows to retrieve pages based on the information they contain; it can answer many queries

Example

Example

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{{#ask: [[Category:City]]}} – show pages with category 
{{#ask: [[has mayor::Klaus Wowereit]]}} – show pages with this data 
{{#ask: [[Category:City]] [[has mayor::Klaus Wowereit]]}} – show pages with both

Results of ask queries are, unless otherwise specified, displayed as customizable tables.

The #ask Query Language (AQL)

The page Semantische Suche provides more information about how to formulate AQL queries.

These slides also contain a nice demonstration about the different parameters that can be used to customize the display of #ask query results.

Main idea

To ask for pages with some specified annotations in order to (in most cases) retrieve additional information from those pages. Those annotations in question are used as query conditions, as illustrated in the examples below:

  • [[Category:City]]
  • [[has mayor::Klaus Wowereit]]

Some query conditions cannot work quite like this:

The AQL query syntax also allows for formulating broader query conditions, for example:

  • [[has population::+]] — pages with some population
  • [[User:+]] — pages in namespace User
  • [[:Category:+]] — pages in namespace Category

AQL Disjunction and Conjunction

Keyword OR can be used to allow alternatives:

{{#ask: [[Category:City]] OR [[Category:Town]] }}

Default behaviour when specifing multiple conditions:
Find pages that satisfy all given conditions (~> this would be AND)

AQL Inverse Properties

It is possible to invert the direction of SMW properties

{{#ask: [[has capital-::Germany]] }}

Here we do not ask for the page that contains a property with the given value but rather for the value of the property entered to the page.

In consequence has capital- has the meaning is capital of.

This can be done in all SMW interfaces that take properties, but not when adding data to a page.

AQL Property Values

We have already seen two types of property values

  • [[has mayor::Klaus Wowereit]] – retrieves all pages with a concrete annotation
  • [[has population::+]] – retrieves pages on which the given property is set regardless of its value

Other conditions based on comparators:

  • [[has population::>1000]] — greater or equal 1000
  • [[has population::<1000]] — less or equal 1000
  • [[has population::!1000]] — inequal 1000
    Note: it always means “has some value for the property that is greater/less/not equal to 1000”

AQL Subqueries

A more elaborate form of property values for Wikipages:
the pages that match another query

Example:
“Countries with small capital cities”
{{#ask: [[has capital::<q>[[has population::<500,000]]</q> ]]}}

Property chains like this can be abbreviated:
{{#ask: [[has capital.has population::<500,000]] }}

“Projects, a research group’s employees are member of”
{{#ask: [[has_member::<q>[[member_of::{{PAGENAME}}]]</q>]] ... }}

Result Formats

SMW provides a number of default formats for displaying the results of #ask queries.

https://www.semantic-mediawiki.org/wiki/Help:Result_formats
provides an overview of the standard result formats shipped with Semantic MediaWiki.

Additional result formats are available via the Extension “Semantic Result Formats”
https://www.semantic-mediawiki.org/wiki/Extension:Semantic_Result_Formats

Letztes Update: 18. September 2024