Properties and Semantic Triples

At the core of SMW are properties, which represent typed relationships between entities. When a property and its value are added to a page, they form a triple: subject → predicate → object.

For example, annotating a page titled "Semantic MediaWiki" with the property "Is related to" and the value "Semantic Forms" creates the triple:

• Subject: Semantic MediaWiki
• Predicate: Is related to
• Object: Sementic Forms

This is expressed in wiki syntax as:

[[Is related to::Semantic Forms]]

These triples mirror the structure of RDF (Resource Description Framework). SMW can export this data as RDF via a dedicated endpoint:

http://edutechwiki.unige.ch/en/Special:ExportRDF/Semantic_MediaWiki

Property Types

Properties in SMW are strongly typed, similar to object-oriented data models. By default, a property’s value is interpreted as a link to another wiki page. How ever, other data types—such as text, number, date, URL, or geocoordinates—can be explicitly defined.

For instance, to store a website URL:

[[Has website::http://www.semantic-mediawiki.org]]

Although the value appears as a URL, SMW treats it as a page link unless the property’s type is explicitly declared. To define a property’s type, you must edit its corresponding property page (e.g., Property:Has website) and add:

This is a property of type [[Has type::URL]].

There are three primary methods to create and define properties:

1. Manual creation: Use the property syntax on any page, then navigate to the property page and assign a type.
2. Create with Form: Use a form interface to select the data type from a dropdown, reducing manual errors.
3. Special:CreateProperty: The most streamlined method—access a dedicated form to define the property name, type, and description in one step.

Displaying Property Values

How a property’s value is rendered depends on its type. Text and number values appear as plain text. Page-type properties render as internal links. URL-type properties may display as clickable links, depending on configuration.

For example, if "Has acronym" is defined as a string type:

[[Has acronym::SMW]]

It will display simply as "SMW", not as a link.

Searching for Properties

To discover all defined properties, use Special:Properties. This page lists all properties, their types, and usage counts. Red links indicate undeclared properties—clicking them allows you to define their type.

Inline Queries

SMW provides a query language accessible via parser functions. The two primary functions are #ask and #show.

• #ask performs a search and returns results formatted according to specified parameters.
• #show retrieves a single property value from a specified page (a shortcut for simple lookups).

A basic query to list all pages in a category:

{{#ask: [[Category:MediaWiki extension]]}}

Outputs: a bulleted list of all pages tagged with that category.

Query Syntax and Filters

Queries follow this structure:

{{#ask: [search conditions] | [display options] | [format options] }}

Search conditions can include:

• Categories: [[Category:MediaWiki extension]]
• Properties: [[Developed with::MediaWiki software]]
• Wildcards: [[Supports languages::+]] (matches any value)
• Comparators: [[Was last edited::>1 September 2013]]
• Partial matches: [[Has field of science::~bio*]] (matches values starting with "bio")

Multiple conditions are combined with logical AND. For OR logic, use the pipe symbol:

{{#ask: [[Category:Extension]] || [[Category:Tool]] }}

Querying Across Categories

By default, category queries include subcategories. For example:

{{#ask: [[Category:MediaWiki extension]]}}

Returns all pages in "MediaWiki extension" and its child categories like "Semantic MediaWiki extensions".

Displaying Multiple Properties

When multiple properties are requested, results appear in a table by default:

{{#ask: 
 [[Category:MediaWiki extension]]
 | ?Has developer
 | ?Last edited
 | ?Has website
}}

This displays a table with the extension name, its developer, last edit date, and website link.

Visualization

SMW supports visual output formats via result formats. For instance, to generate a chart of developers:

{{#ask: 
 [[Has developer::Yaron Koren]]
 | ?Has developer
 | ?Has name
 | format=category
}}

Can render as a tag cloud or graph, depending on installed extensions like Semantic Result Formats.

Query Limits and Debugging

By default, #ask limits results to 50 entries. Override this with the limit parameter:

{{#ask: ... | limit=100 }}

To debug queries, enable the debug parameter to see the underlying SPARQL-like query structure.

Special Properties and Composite Data

SMW includes built-in special properties, such as:

• Has page language
• Was last edited
• Page namespace

These are automatically populated and can be viewed and configured via Special:Properties. To enable them, click the red link and assign a type (e.g., text, date).

Handling Complex Data with Subobjects

SMW’s page-centric model struggles with compound data like "Teacher has three bananas." To represent such relationships, use semantic subobjects:

{{#subobject:banana1
 | has quantity=3
 | has color=yellow
}}

Subobjects allow nested data structures within a single page, enabling modeling of real-world relationships without requiring separate pages for each component.