define the design of the implementation

[lgiessmann]

Common Form
((PREFIX bounding: <uri-prefix>)|(PREFIX : <uri-prefix>)*
(BASE <base-uri>)*)*
SELECT ?varName+
WHERE {
(({?subjectOrVarName predicateOrVarName objectOrVarName}?)*
({?FILTER (filterExpression)}?)*
(BASE <base-uri>)*)*
}

Grouping
{}

Base
BASE <uri>
…
<book>

-> uri/book

Literals
(“anyCharacter*“)|(‘anyCharacter*‘)((^{anyUri)|(@languageTag)){0,1}}

Variables
($anyChar*)|(?anyChar*)
?var = $var

Predicate object-lists
?x foaf:name ?name ;

foaf:mbox ?mbox .

This is the same as writing the triple patterns:

?x foaf:name ?name .
?x foaf:mbox ?mbox .

rdf:type
rdf:type = a

Empty Graph Pattern
The group pattern:
{ }
matches any graph (including the empty graph) with one solution that does not bind any variables. For example:
SELECT ?x
WHERE {}
matches with one solution in which variable x is not bound.