Expressions

The Expression is the interface for all expressions used in SPARQL Requests.

Types of expressions

The types of expressions can be:

• The LiteralExpression class is used for literals
• The IRIExpression class is used for IRIs
• The VariableExpression class is used for expressions which only are a variable^[1]
  For example for the ORDER BY ?var expression
• The QualifiedNameExpression class is used for expressions which only encapsulate a qualified name
• The ArithmeticExpression class is used for arithmetic expressions^[2]
  For example for the BIND (?index * 2 as ?var) expression
• The FunctionExpression class is used for functions expressions^[3]
  For example for the SELECT ?zone (floor(?altitude) AS ?alt) expression
• The ComparisonExpression class is used for comparison expressions^[4]
  For example for the FILTER (?index < 5) expression

Function expressions

Function expressions can appear in SELECT, BIND, FILTER, or COALESCE expressions. For example:

   SELECT ?country (COUNT(?city) AS ?TotalCity)
   WHERE {  
      ?city ge:isLocatedIn ?country . 
      ?city rdf:type ge:City .
   } 
   GROUP BY ?country

Expression variables

Used variables

The Expression.getVariables() return the names of all the variables used in the expression.

For example:

• For the following expression:

  ?city + ?name
  

• The method will return the city and name names

Produced variables

The Expression.getVariables() return the names of all the variables produced by the expression.

For example:

• For the following expression:

  ?city + ?name
  

• The method will return the city and name names

And:

• For the following expression:

  ?city > ?name
  

• The method will return an empty set

Creating an expression

There are two ways to create an expression:

• Using the API to combine expressions
• Parsing an expression from a String