7.13 Automatic Variable Renaming

Automatic variable renaming can enable certain queries that previously failed to run successfully.

Previously, variable names used in SPARQL queries were passed directly on to Oracle Database as a part of a SQL statement. If the variable names included a SQL or PL/SQL reserved keyword, the query failed to execute. For example, the following SPARQL query used to fail because the word date as a special meaning to the Oracle Database SQL processing engine.

select ?date { :event  :happenedOn ?date }

Currently, this query does not fail, because a "smart scan" is performed and automatic replacement is done on certain reserved variable names (or variable names that are very long) before the query is sent to Oracle database for execution. The replacement is based on a list of reserved keywords that are stored in the following file embedded in sdordfclient.jar:

oracle/spatial/rdf/client/jena/oracle_sem_reserved_keywords.lst

This file contains over 100 entries, and you can edit the file to add entries if necessary.

The following are examples of SPARQL queries that use SQL or PL/SQL reserved keywords as variables, and that will succeed because of automatic variable renaming:

• Query using SELECT as a variable name:

  PREFIX foaf: <http://xmlns.com/foaf/0.1/>
  select ?SELECT ?z
  where
  {    ?SELECT foaf:name ?y.
       optional {?SELECT foaf:knows ?z.}
  }
  

• Query using ARRAY and DATE as variable names:

  PREFIX x:    <http://example.com#>
  construct {
      ?ARRAY x:date ?date .
  }
  where {
      ?ARRAY x:happenedOn ?date .
  }