Parser implementation

* Adaptation of the grammar to make more regular w.r.t reference space
   names placement.

 * Implemented Type check

 * Implemented prediction of the result set cardinality. This assumes:
    + A space is not infinite, this is required to compute complementary
      sets as we can compute the whole space volume.
    + Density is mostly uniform, this allows us to assume the number of
      results is related with a constant factor to the volume in space
      of the selection.
    + The prediction is approximated by using the most pessimistic
      resulting cardinality for each operator, in order to keep the
      operation simple, and fast, at the expense of the precision.

 * Implemented execution, which calls into a DB abstraction layer. That
   layer is currently mostly empty. Execution is also implemented in a
   naive way, and should most likely be optimised.

Grammars/filters.g4

@@ -134,33 +134,38 @@ hyperrectangle
     : 'hyperrectangle' '{'
           position ',' position
           ( ',' position ',' position )*
+          ( ',' STRING )?
        '}'
     ;
 
 /* A hypersphere is defined by its center and a radius, independantly
  * of the number of dimensions of the space. */
 hypersphere
-    : 'hypersphere' '{' position ( ',' positive_number ) '}'
+    : 'hypersphere' '{'
+           position
+           ',' positive_number
+           ( ',' STRING )?
+        '}'
     ;
 
 point
-    : 'point' '{' position '}'
+    : 'point' '{' position ( ',' STRING )? '}'
     ;
 
 /* Define a shape as the non-zero values in a NIfTI object, defined by
  *   nifti{
- *     spaceId: string,
  *     lower_corner: position,  // Optional, default to the origin
  *     rotation: [ position+ ], // Optional, no rotation by default
- *     bytes: uri(STRING)       // uri to the NIfTI object
+ *     bytes: uri(STRING),      // uri to the NIfTI object
+ *     spaceId: string
  *   }
  */
 nifti
     : 'nifti' '{'
-        STRING ','
         (position ',' )?
         ( '[' position ( ',' position )* ']' ',' )?
-        byte_provider
+        byte_provider ','
+        STRING
       '}'
     ;
 

Grammars/queries.g4

@@ -18,11 +18,11 @@ projection_operators
  *
  * If it is provided, it MUST resolve to a NUMBER. */
 nifti_operator
-    : 'nifti' '(' ( selector ',' )? bag_expression ')'
+    : 'nifti' '(' ( STRING ',' )? ( selector ',' )? bag_expression ')'
     ;
 
 json_operator
-    : 'json' '(' jslt ',' bag_expression ')'
+    : 'json' '(' jslt ',' bag_expression ( ',' STRING )? ')'
     ;
 
 jslt