Help:Displaying information
Queries in Semantic MediaWiki return a list of pages, and the default result of a query therefore simply displays the selected pages' titles. Additional information such as a page's property values or categories, can be included into a query result by using additional printout statements that are introduced here. In Special:Ask, printout statements can simply be entered into the input box on the right, with one statement per line.
There are different kinds of printout statments, but all of them can be recognised by the question mark ? that they start with. The important difference between printout statements and query descriptions is that the former do not restrict the result set in any way: even if some printout has no values for a given page, an empty field will be printed, but the page is still part of the result.
Printing property values[edit]
The most common form of printout statements are property printouts, that make SMW display all values assigned to a certain property. These are written simply as a question mark followed by the property name, e.g.
?population
prints the values for «population» of all query results. On Special:Ask, the result of each printout is shown in a table column that is labelled by the name of the property. It is possible to change that label for a printout, and this will be very useful when using queries on wiki pages (it is not really relevant on Special:Ask of course). The equality symbol is used to change the label:
?population = Number of inhabitants
The above still prints population, but with the modified label in the table header. As mentioned above, property printouts may have an empty result for some pages, e.g. if something does not have any population. Property conditions with wildcards (see above) can be used to ensure that all elements in a query result have some value for the printed property, if this is desired.
Printing categories[edit]
There are two ways to print category information: either SMW prints all categories assigned to some page, or SMW checks for one particular category. The first case is achieved by the printout
?Category
where «Category» is the name of the Category namespace in the local language. This printout will show all catgories that are directly used on a result page. The other option is to ask for one particular category, such as
?Category:Actor
The result then will contain a column «Actor» that contains X for all pages that directly belong to that category, and is empty otherwise. Again, one can change the label using equality:
?Category:Actor = A
will merely display an «A» as the header of the result column which might be more sensible given that the entries in that column are very short. It is also possible to change the way in which this kind of category queries are formatted, as described below.
The main result column[edit]
All queries by default display the main list of result pages in the first column. In some cases, it can be useful to move that to another position. This is not relevant for Special:Ask, but can be quite useful in inline queries. A special printout statment is available for this purpose:
?
This single question mark addresses the «unlabelled result column» that shows the main result list. As before, different labels can be assigned with the equality symbol, e.g.
? = Results
Display format[edit]
Many printout statements can be further customised by giving a printout format which can be given after a property name, separated by the symbol #.
For properties that support units, queries can thus determine which unit should be used for the output. To print the height in cm, e.g., one would use the following:
?height#cm
this assumes that the property height is aware of the unit «cm». Datatypes other than Type:Number may have different printout formats. See the types documentation for details.
For printouts of the form ?Category:Actor, the display format can be used to modify what SMW will display for cases where a page is (or is not) in the category. The following is an example:
?Category:Actor#an actor, not an actor
This will show the text «an actor» for all pages that are actors, and the text «not an actor» otherwise. This can, for example, also be used in combination with small images to display icons for certain categories.
