program
::= assignment | expression
assignment
::= identifier ( "≔" | ":=" ) expression
expression
::= relation-identifier
| union
| intersection
| difference
| cartesian-product
| selection
| projection
| rename
| join
| "(" expression ")"
/* ************************************************************************* */
union ::= expression ( "∪" | "union" ) expression
intersection
::= expression ( "∩" | "intersect" ) expression
difference
::= expression ( "∖" | "-" | "diff" ) expression
cartesian-product
::= expression ( "⨯" | "×" | "product" ) expression
selection
::= expression
( "σ" | "select" ) "[" criteria ("," criteria )* "]"
expression
criteria
::= ( attribute-identifier | literal )
operation
( attribute-identifier | literal )
operation
::= "=" | "!=" "<" | "<=" | ">" | ">="
projection
::= expression
( "Π" | "π" | ""project" ) "[" attribute-identifier ("," attribute-identifier )* "]"
expression
rename ::= expression
( "ρ" | "rename" ) "[" rename-pair ("," rename-pair )* "]"
expression
rename-pair
::= attribute-identifier "=" attribute-identifier
join ::= expression
( natural-join | theta-join )
expression
natural-join
::= "⨝" | "natural-join"
theta-join
::= ( "⨝" | "theta-join" ) "[" criteria ("," criteria )* "]"
/* ************************************************************************* */
relation-identifier
::= ALPHA ( ALPHANUM | "_" )*
attribute-identifier
::= relation-identifier
( "." ( relation-identifier | integer ) )
/* ************************************************************************* */
literal ::= integer | string | boolean
integer ::= DIGIT+
string ::= '"' [^\"]* '"'
boolean ::= "true" | "false"
