Squish queries for schemarama

Often we need to know whether a particular tool will work with a particular piece of RDF. This example validates an RDF file describing an image, for display in the codepiction demo.

Query Language summary

The RDF query server used by these forms accepts the following query language, similar to R. V. Guha's RDFDB QL:

SELECT variables [FROM url, url] WHERE (pred variable/string variable/string) .... () () [AND constraint] [USING predString FOR predUrl]
variables must start with a ? and contain no spaces
the arguments to FROM are urls which are de-serialized and treated as the basis for the query. If there is no FROM clause the a default SQL database will be used.
pred can be a predicate string e.g dc::title or a full property name. If a predicate string, add on a USING clause to specify what the predicate string stands for (e.g. USING dc FOR http://purl.org/dc/1.1/)
constraints can be variable > | < | = | > =| < = | ~ value where value should be an integer, except in the case of ~ where it should be a string