Add 'row in scope' approach

Author: afs

spec/index.html

@@ -10429,7 +10429,7 @@ Evaluation Semantics
           
             Values Insertion and `EXISTS`
 
-            The following subsections contain draft of material for a revised
+            The following subsections contain draft material for a revised
               "`exists`" operation.
             
             
@@ -10444,7 +10444,10 @@ Syntax Restriction
                 This applies to `BIND`, variables introduced by `AS` in a `SELECT` clause, variables in a `VALUES`
                 clause, and variables introduced by `AS` in `GROUP BY`.
               
-              Extend the "in-scope" rules to include the variables in-scope from the current row:
+              
+                Extend the "in-scope" rules to include the possible 
+                variables that are in-scope for the current row:
+              
@@ -10458,10 +10461,15 @@ Syntax Restriction
                 
                   
@@ -10458,10 +10461,15 @@ Syntax Restriction
                   
                 
               
-              
-                This restriction means that values inserted
-                do not conflict with values assigned to variables within the pattern.
-              
+
+                
+                  This restriction means that values inserted
+                  do not conflict with values assigned to variables within the pattern.
+                
+                
+                  This operation is performed as part of query parsing.
+                
+              
             
             
               Remapping
@@ -10486,7 +10494,7 @@ Remapping
                 F(v) = v1 if v is in PV, where v1 is a fresh variable
 F(v) = v if v is not in PV
                 
-                Define the Projection Expression Variable Remapping `ProjectMap(P,PV)`
+                Define the Projection Expression Variable Remapping `ProjectMap(P, PV)`
                 
                 ProjectMap(Project(A, PV)) = Project(A1, PV) 
                                 where A1 is the result of applying F
@@ -10514,39 +10522,88 @@ Remapping
                 Replacements may happen several times, depending on recursive order
                 but each time a replacement is made, the variable not used anywhere else.
               
-        
-              
-                A variable inside a project expression that is not in the variables projected
-                is not affected by the values insertion operation because it is renamed apart.
-              
+
+
+                
+                  A variable inside a project expression that is not in the variables projected
+                  is not affected by the values insertion operation because it is renamed apart.
+                
+                
+                  This operation is as part of the translation to the SPARQL
+                  algebra.
+                
+              
             
             
               Values Insertion
+              
+                Alternative 1: rewrite the algebra during 
+                translation to the SPARQL algebra
+                to include a function that evaluates to the current row.
+              
+
 
 
-                  Definition: defn_valuesinsertion" name="defn_valuesinsertion">Values Insertion
+                  Definition: defn_correlate" name="defn_correlate">Values In Scope
                   
-                    Define the Values Insertion function `ValuesInsert(X, μ)`
+                    Define the function `BindingInScope()`. 
+                    Evaluation of `BindingInScope()` results in a table of one row,
+                    being the current binding of the enclosing filter.
                   
-                  Let Table(μ) = { μ } and multiplicity( μ | Table(μ) = { μ } ) = 1
+                
+              
 
+
+
+                  Definition: Access to the current binding
+                  
+                    During translation to the SPARQL algebra
+                  
+                  
 Replace each occurence of `Y` in X where `Y` is one of
           Basic Graph Pattern,
           Property Path Expression,
           `Graph(Var, pattern)`,
           Inline Data
-with `join(Y, Table(μ))`.
-
+          with `join(Y, BindingInScope())`.
+                
+
+                  c.f. section Translate Graph Patterns
+                  where an empty basic graph pattern start any 
+                  GroupGraphPattern.
+                  It happens before the simplification step.
                 
-                @@ rename as ???correllate
               
 
 
                 
                   Examples
                 
               
+
+              
+                Alternative 2: rewrite the algebra during execution. This corresponds to the 
+                original SEP-0007 proposal.
+              
+
+
+                  Definition: Values Insertion
+                  
+                    Define the Values Insertion function `ValuesInsert(X, μ)`
+                  
+                  Let Table(μ) = { μ } and multiplicity( μ | Table(μ) = { μ } ) = 1
+
+Replace each occurence of `Y` in X where `Y` is one of
+          Basic Graph Pattern,
+          Property Path Expression,
+          `Graph(Var, pattern)`,
+          Inline Data
+with `join(Y, Table(μ))`.
+
+                
+              
             
+
             
               Evaluation of EXISTS
 
@@ -10556,7 +10613,7 @@ Evaluation of EXISTS
                       define the Evaluation of Exists `exists(X)`
                 
                 exists(X) = true 
-              if eval( D(G), ValuesInsert(PrjMap(X), μ) )
+              if eval( D(G), ValuesInScope(PrjMap(X)), μ)
                  is a non-empty solution sequence.
 exists(X) = false otherwise