2.5.1. BNF grammar#
The terminal elements are in capital letters, non-terminal in lowercase. The value of the terminal elements (between quotes) is a Python regular expression.
statement ::= (select | delete | insert | update) ';' # select specific rules select ::= 'DISTINCT'? E_TYPE selected_terms restriction? group? sort? selected_terms ::= expression ( ',' expression)* group ::= 'GROUPBY' VARIABLE ( ',' VARIABLE)* sort ::= 'ORDERBY' sort_term ( ',' sort_term)* sort_term ::= VARIABLE sort_method =? sort_method ::= 'ASC' | 'DESC' # delete specific rules delete ::= 'DELETE' (variables_declaration | relations_declaration) restriction? # insert specific rules insert ::= 'INSERT' variables_declaration ( ':' relations_declaration)? restriction? # update specific rules update ::= 'SET' relations_declaration restriction # common rules variables_declaration ::= E_TYPE VARIABLE (',' E_TYPE VARIABLE)* relations_declaration ::= simple_relation (',' simple_relation)* simple_relation ::= VARIABLE R_TYPE expression restriction ::= 'WHERE' relations relations ::= relation (LOGIC_OP relation)* | '(' relations')' relation ::= 'NOT'? VARIABLE R_TYPE COMP_OP? expression | 'NOT'? R_TYPE VARIABLE 'IN' '(' expression (',' expression)* ')' expression ::= var_or_func_or_const (MATH_OP var_or_func_or_const) * | '(' expression ')' var_or_func_or_const ::= VARIABLE | function | constant function ::= FUNCTION '(' expression ( ',' expression) * ')' constant ::= KEYWORD | STRING | FLOAT | INT # tokens LOGIC_OP ::= ',' | 'OR' | 'AND' MATH_OP ::= '+' | '-' | '/' | '*' COMP_OP ::= '>' | '>=' | '=' | '<=' | '<' | '~=' | 'LIKE' FUNCTION ::= 'MIN' | 'MAX' | 'SUM' | 'AVG' | 'COUNT' | 'UPPER' | 'LOWER' VARIABLE ::= '[A-Z][A-Z0-9]*' E_TYPE ::= '[A-Z]\w*' R_TYPE ::= '[a-z_]+' KEYWORD ::= 'TRUE' | 'FALSE' | 'NULL' | 'TODAY' | 'NOW' STRING ::= "'([^'\]|\\.)*'" |'"([^\"]|\\.)*\"' FLOAT ::= '\d+\.\d*' INT ::= '\d+'
2.5.2. Internal representation (syntactic tree)#
The tree research does not contain the selected variables (e.g. there is only what follows “WHERE”).
The insertion tree does not contain the variables inserted or relations defined on these variables (e.g. there is only what follows “WHERE”).
The removal tree does not contain the deleted variables and relations (e.g. there is only what follows the “WHERE”).
The update tree does not contain the variables and relations updated (e.g. there is only what follows the “WHERE”).
Select ((Relationship | And | Or)?, Group?, Sort?) Insert (Relations | And | Or)? Delete (Relationship | And | Or)? Update (Relations | And | Or)? And ((Relationship | And | Or), (Relationship | And | Or)) Or ((Relationship | And | Or), (Relationship | And | Or)) Relationship ((VariableRef, Comparison)) Comparison ((Function | MathExpression | Keyword | Constant | VariableRef) +) Function (()) MathExpression ((MathExpression | Keyword | Constant | VariableRef), (MathExpression | Keyword | Constant | VariableRef)) Group (VariableRef +) Sort (SortTerm +) SortTerm (VariableRef +) VariableRef () Variable () Keyword () Constant ()
2.5.3. Known limitations#
The current implementation does not support linking two relations of type ‘is’ with an OR. I do not think that the negation is supported on this type of relation (XXX to be confirmed).
missing COALESCE and certainly other things…
writing an rql query requires knowledge of the used schema (with real relation names and entities, not those viewed in the user interface). On the other hand, we cannot really bypass that, and it is the job of a user interface to hide the RQL.
It would be convenient to express the schema matching relations (non-recursive rules):
Document class Type <-> Document occurence_of Fiche class Type Sheet class Type <-> Form collection Collection class Type
Therefore 1. becomes:
Document X where X class C, C name 'Cartoon' X owned_by U, U login 'syt' X available true
I’m not sure that we should handle this at RQL level …
There should also be a special relation ‘anonymous’.