--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/doc/book/en/annexes/rql/implementation.rst	Thu May 07 16:33:22 2009 +0200
@@ -0,0 +1,169 @@
+
+
+Implementation
+--------------
+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+'
+
+
+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       ()
+
+
+Known limitations
+~~~~~~~~~~~~~~~~~
+
+- The current implementation does not support linking two relations of type 'is'
+  with a OR. I do not think that the negation is supported on this type of
+  relation (XXX FIXME to be confirmed).
+
+- Relations defining the variables must be left to those using them.  For
+  example::
+
+     Point P where P abs X, P ord Y, P value X+Y
+
+  is valid, but::
+
+     Point P where P abs X, P value X+Y, P ord Y
+
+  is not.
+
+- missing proper explicit type conversion,  COALESCE and certainly other things...
+
+- writing a rql query require knowledge of the schema used (with real relation
+  names and entities, not those viewing in the user interface). On the other
+  hand, we can not really bypass that, and it is the job of a user interface to
+  hide the RQL.
+
+
+Topics
+~~~~~~
+
+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'.