The following is adapted from Filter encoding specifications:
- Filter Encoding 1.0
- OpenGIS® Filter Encoding Implementation Specification Version 1.1
- OpenGIS® Catalogue Service Implementation Specification 2.0.1
An expression can be formed using the elements:
Function. They all belong to the substitution group
expression which means that any of them can be used wherever an expression is called for. In
addition, the combinations of these elements are themselves expressions and can be used wherever
an expression is called for.
The elements defined in this package are used to encode the fundamental arithmetic operations of addition, subtraction, multiplication and division. Arithmetic operators are binary operators meaning that they accept two arguments and evaluate to a single result.
A literal value is any part of a statement or expression that is to be used
exactly as it is specified, rather than as a variable or other element. The
Literal element is used to encode literal scalar and
A function is a named procedure that performs a distinct computation. A
function may accept zero or more arguments as input and generates a single result. A function is
composed of the name of the function, encoded using the attribute name, and zero or more
arguments contained within the
Function element. The
arguments themselves are expressions.
Data access is acomplished by means of
PropertyName expressions. These Expressions are independent
of the data being queried and form the foundation of a, very simple, general query language
offering independence specific bindings to Feature, Metadata and Record data structures.
At the time of this writing the Filter API has standard encodings for XML (Filter 1.0 and Filter 1.1) and Text (a BNF form is provided in the Catalog 2.0.1 specification above). You should be warned that not all content can be expressed in all encodings, please refer to the javadocs for specific limitations.
Interface Summary Interface Description AddEncodes the operation of addition. BinaryExpressionAbstract base class for the various filter expressions that compute some value from two input values. DivideEncodes the operation of division where the first argument is divided by the second argument. ExpressionInterface for all the OGC Filter elements that compute values. ExpressionVisitorVisitor with
visitmethods to be called by
FunctionInstances of this class represent a function call into some implementation-specific function. InternalFunctionSpecial
Functiontype indicating that that the function is to be executed exclusively at run-time, and does not participate in the SPI (Service Provider Interface) lookup mechanism (i.e.
LiteralInstances of this interface provide a constant, literal value that can be used in expressions. MultiplyEncodes the operation of multiplication. PropertyNameExpression class whose value is computed by retrieving the value indicated by the provided name. SubtractEncodes the operation of subtraction where the second argument is subtracted from the first. VolatileFunctionMarker interface indicating that that the function return value can change during a single data access operation even if the argument values provided to it remain constant
Class Summary Class Description NilExpressionPlaceholder class used to represent a NIL expression, evaluates to