问题
I am trying to fill the empty spaces generated by the use of Optional in the SPARQL query language. Are there any ways that I can achieve this?
The use of !bound on the optional variable generates true or false, but I want to fill the cells with my own values such as "?" or "unknown".
回答1:
Perhaps you could use one of the following constructs...
COALESCE(?c, "unknown")
Source: http://www.w3.org/TR/sparql11-query/#func-coalesce
or
IF(bound(?c), ?c, "unknown")
Source: http://www.w3.org/TR/sparql11-query/#func-if
来源：https://stackoverflow.com/questions/19723721/generating-values-for-empty-attributes