Encapsulates basic literals such as Strings, Integers and Real numbers The Comparison operators such as Less-than or More-than, etc Operators for expressing a single element operation Used for expressing operations like A+B Represents a table with its name and its alias name Same as a tableType with an additional archive name Used for adding a table for the Xmatch operation Used for avoiding a table in Xmatch Represents a column Represents an unary expression such as -(a.ra) Represents a binary expression such as a+b Represents an expression inside a bracket A function expression, one of math,trigonometri or aggregate function Enumeration of allowed trigonometric functions Enumeration of allowed aggregate functions Enumeration of allowed math functions Option of selecting all or distinct elements in a query Represent all columns as in Select * query A cross match expression Used inside an xmatch for speccifying distance The Like expression of a query The Not Like expression of a query Represents the Between expression of a query Represents the Not Between expression of a query Represents the Comparison of two expressions Represents expressions like A Or B Represents expressions like A And B Represents expressions like Not A Represents expressions like (A) Represents the Having expression part of a query Represents the Group By expression part of a query Represents the Where part of the query Represents the From part of the query List of items to be selected in the Query Used to selecting an expression as a new alias column Represents the TOP part of a query Ascending or Descending order of an Order by term Option for setting the direction for Order By Represents the ORDER BY part of a query List of expressions in which order the results should be provided The SELECT part of a query The only permitted root element of a query, the SELECT element