de.up.ling.irtg.algebra

Class Algebra<E>

java.lang.Object

de.up.ling.irtg.algebra.Algebra<E>

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

BinarizingAlgebra, EvaluatingAlgebra, SetAlgebra, StringAlgebra, TagStringAlgebra, TagTreeAlgebra, TreeAlgebra

public abstract class Algebra<E>
extends Object
implements Serializable

An algebra over some domain E of values. An algebra can evaluate a term t over the algebra's signature to an object in E. If the algebra is furthermore regularly decomposable -- i.e., we can compute a tree automaton for the terms denoting some object in E --, the algebra can be used as the input algebra in IRTG parsing.

A concrete implementation of this abstract base class must provide two methods, evaluate(java.lang.String, java.util.List) and parseString(java.lang.String). The evaluate method interprets its first argument (a string) as a function symbol of the algebra, and applies it to the given arguments. The parseString method translates a string representation of a value of this algebra into the value itself. The Algebra class then implements a default implementation of the method evaluate(de.up.ling.tree.Tree), which evaluates an entire term of the algebra. You may override the evaluate-term method with a specialized implementation if this is more efficient.

The Algebra class also provides a default implementation of decomposition automata for this class. Decomposition automata are needed for parsing. The default implementation uses values of the algebra as its states, and only provides bottom-up rules which simply evaluate the terminal symbol on the child "states". This default implementation will allow you to get started with parsing quickly, but if you want to achieve reasonably parsing efficiency, you will almost certainly want to implement your own optimized decompose method eventually.

Author:

koller

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Algebra() Constructs a new instance which is based on a newly created Signature.

Method Summary

Modifier and Type	Method and Description
TreeAutomaton	decompose(E value) Computes a decomposition automaton for the given value.
E	evaluate(Tree<String> t) Evaluates a term over the algebra's signature into an algebra object.
static Iterator<Class>	getAllAlgebraClasses() Returns an iterator over all subclasses of Algebra.
Class	getClassOfValues() Returns the class of the elements of this algebra.
Signature	getSignature() Returns the signature of this algebra.
boolean	hasOptions() Returns true if the algebra implementation has options that would make sense to be set using setOptions(java.lang.String).
abstract E	parseString(String representation) Resolves the string representation of some element of the algebra's domain to this element.
void	readOptions(Reader optionReader) Sets the options of the algebra implementation.
String	representAsString(E object) Returns a string representation of this object.
void	setOptions(String string) Sets the options of the algebra implementation from a string.
JComponent	visualize(E object) Returns a Swing component that visualizes an object of this algebra.
void	writeOptions(Writer optionWriter) Writes the options of the current algebra object to a Writer.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Algebra

public Algebra()

Constructs a new instance which is based on a newly created Signature.

Method Detail

evaluate

public E evaluate(Tree<String> t)

Evaluates a term over the algebra's signature into an algebra object.

Parameters:

t - a term (= tree whose nodes are labeled with algebra operation symbols)

Returns:

getSignature

public Signature getSignature()

Returns the signature of this algebra.

Returns:

decompose

public TreeAutomaton decompose(E value)

Computes a decomposition automaton for the given value. A decomposition automaton is a finite tree automaton which accepts exactly those terms over the algebra's signature which evaluate to the given value.

Parameters:

value -

Returns:

parseString

public abstract E parseString(String representation)
                       throws ParserException

Resolves the string representation of some element of the algebra's domain to this element. For instance, the method TreeAlgebra.parseString(java.lang.String) resolves the string "f(a,b)" into a tree with three nodes.

It is the job of an algebra class to keep track of the signature of the algebra. Many algebras have a potentially infinite domain (e.g. the string algebra can be used with arbitrary alphabets), so the algebra class should keep track of the symbols that were actually used in the current run of the program. The best practice is to update the signature each time the parseString method is called. The rest of the IRTG tool code takes care to call parseString of the respective algebra to obtain objects of type E, so this ensures that the signature is always up-to-date.

Parameters:

representation -

Returns:

Throws:

ParserException

readOptions

public void readOptions(Reader optionReader)
                 throws Exception

Sets the options of the algebra implementation. Most algebras do not have options; for these algebras, it is okay to reuse the default implementation of readOptions, which simply does nothing. However, if your algebra relies on external data to work properly, you may provide a reader that provides a string representation of this external data using this method. See SetAlgebra for an example.

Parameters:

optionReader -

Throws:

Exception

setOptions

public void setOptions(String string)
                throws Exception

Sets the options of the algebra implementation from a string. This method simply wraps the option string into a StringReader and then calls readOptions(java.io.Reader).

Parameters:

string -

Throws:

Exception

See Also:

readOptions(java.io.Reader)

writeOptions

public void writeOptions(Writer optionWriter)
                  throws Exception

Writes the options of the current algebra object to a Writer.

Parameters:

optionWriter -

Throws:

Exception

See Also:

readOptions(java.io.Reader)

hasOptions

public boolean hasOptions()

Returns true if the algebra implementation has options that would make sense to be set using setOptions(java.lang.String).

Returns:

visualize

public JComponent visualize(E object)

Returns a Swing component that visualizes an object of this algebra. The default implementation simply returns a JLabel containing a string representation of the algebra object. Override this method to provide more human-readable graphical presentations.

Parameters:

object -

Returns:

representAsString

public String representAsString(E object)

Returns a string representation of this object. The default implementation simply calls the object's Object.toString() method. Concrete algebras may overwrite this implementation for algebra-specific string representations. Whenever Alto knows to which algebra an object belongs, it will attempt to call this method instead of the generic toString to produce algebra-specific string representations.

Parameters:

object -

Returns:

getClassOfValues

public Class getClassOfValues()

Returns the class of the elements of this algebra. The default interpretation simply returns Object; you may override this with the actual class of the objects of your algebra.

This method is used in some places throughout Alto to figure out what OutputCodecs are appropriate for encoding objects of the algebra. By overriding the method to return more specific classes than Object, you make more output codecs available in those places.

Returns:

getAllAlgebraClasses

public static Iterator<Class> getAllAlgebraClasses()

Returns an iterator over all subclasses of Algebra. This is used for finding all available types of algebras.

Returns: