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It should be noted that SearchSelector can also be used for 'non-canned' searches: we could expose a search box in a web page, have the user type in a search string and configure a search selector to use this 'live' query.
QuerySelector
This selector queries the database to obtain its objects. In essence, the selector transforms a very simplified user-supplied query string into the SQL necessary to perform the database query. An example can illustrate:
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in_archive = '1' AND last_modified > ${today - 7} AND dc.contributor.author = 'Jones'
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This query would retrieve all items authored by Jones installed within the last week. The actual SQL is more complex, since joins with the metadata tables are required. For the curious, the syntax of the query language is given below (in Extended Backus-Naur Form)
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(* Query syntax EBNF *)
query = expr , { "AND" , expr } ;
expr = field name | metadata name , oper , value ;
field name = characters , { "_" , characters } ;
metadata name = characters , "." , characters , [ "." , characters ] ;
oper = "=" | "<>" | ">" | "<" | ">=" | "<=" | "BETWEEN" | "LIKE" | "IN" ;
value = literal | variable ;
literal = "'" , characters , { whitespace , characters } , "'" ;
variable = "${" , varname , [ "+" | "-" , number ] , "}" ;
varname = "today" | handle ;
(* end syntax EBNF *)
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