com.saxonica.ee.schema.fsa

Class FiniteStateMachine

java.lang.Object

com.saxonica.ee.schema.fsa.FiniteStateMachine

public class FiniteStateMachine
extends Object

Class representing a finite state machine, as a collection of states with transitions between them.

The finite state machine allows states with counters. The static machine created by the schema compiler contains states of type AutomatonState; these may have a minOccurs and maxOccurs value. When such a state is entered at validation time, a CountingState is dynamically created that contains a pointer to the fixed AutomatonState plus an integer counter. Any transition that goes from the state to itself causes a new CountingState to be created with an incremented value of the counter (provided it does not exceed the maxOccurs()); any transition to a different state causes the counter to be checked against the minOccurs value.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	FiniteStateMachine.TermParticlePair

Constructor Summary

Constructors

Constructor and Description
FiniteStateMachine(UserComplexType type, boolean determinized) Create a finite state machine

Method Summary

Methods

Modifier and Type	Method and Description
void	allocateStateNumber(AutomatonState state) Allocate a unique number to a state, and index the state from the FSM
static NonDeterminizedState	compileParticle(SchemaCompiler compiler, Particle particle, NonDeterminizedState endState, UserComplexType subjectType, FiniteStateMachine machine) Static method to translate a particle to a Finite State Automaton, returning the start state of the FSA.
static FiniteStateMachine	determinize(SchemaCompiler compiler, FiniteStateMachine nfsa) Determinize the finite state machine: that is, ensure that there are no ambiguous transitions from this state.
void	display(Logger err) Display the finite state machine.
AutomatonState	getInitialState() Get the initial state of this finite state machine
int	getNumberOfStates() Determine the number of states in this finite state machine
Wildcard	getOpenContentWildcard() Get the open content wildcard, if any
AutomatonState	getState(int number) Get the state with a given unique state number
boolean	isOpenContentInterleaved() Ask whether the open content wildcard for this finite state machine (assuming there is one) permits interleaved content (as opposed to suffixed content only)
void	serialize(SchemaModelSerializer serializer) Output a reppresentation of this finite state machine
void	setInitialState(AutomatonState initialState) Set the initial state of this finite state machine
void	setOpenContentWildcard(Wildcard wildcard, boolean interleaved) Set the open content wildcard for this machine
static String	subsumesMachine(FiniteStateMachine base, FiniteStateMachine sub, SchemaCompiler compiler) Test whether one finite state machine subsumes another FSM: that is, whether for each path through the second FSM, there is a corresponding path through the first FSM.

Methods inherited from class java.lang.Object

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

Constructor Detail

FiniteStateMachine

public FiniteStateMachine(UserComplexType type,
                  boolean determinized)

Create a finite state machine

Parameters:

type - the type whose content model is implemented by this finite state machine

determinized - true if this machine is determinized

Method Detail

allocateStateNumber

public void allocateStateNumber(AutomatonState state)

Allocate a unique number to a state, and index the state from the FSM

Parameters:

state - the state whose number is to be allocated

getNumberOfStates

public int getNumberOfStates()

Determine the number of states in this finite state machine

Returns:

the number of states

getInitialState

public AutomatonState getInitialState()

Get the initial state of this finite state machine

Returns:

the initial state

setInitialState

public void setInitialState(AutomatonState initialState)

Set the initial state of this finite state machine

Parameters:

initialState - the initial state

getState

public AutomatonState getState(int number)

Get the state with a given unique state number

Parameters:

number - the number of the state

Returns:

the state with this unique state number

setOpenContentWildcard

public void setOpenContentWildcard(Wildcard wildcard,
                          boolean interleaved)

Set the open content wildcard for this machine

Parameters:

wildcard - the open content wildcard (may be null)

interleaved - true if open content may be interleaved, false if it must be suffixed

compileParticle

public static NonDeterminizedState compileParticle(SchemaCompiler compiler,
                                   Particle particle,
                                   NonDeterminizedState endState,
                                   UserComplexType subjectType,
                                   FiniteStateMachine machine)
                                            throws SchemaException,
                                                   UnresolvedReferenceException

Static method to translate a particle to a Finite State Automaton, returning the start state of the FSA. This precisely follows Henry Thompson's and Richard Tobin's algorithm, published here

Parameters:

compiler - user for error reporting

particle - the particle to be compiled, which is either an ElementDeclaration, a WildCard, a choice, or a sequence

endState - the State representing the final state of the automaton

subjectType - the complex type to which this particle belongs

machine - the finite state machine to which the state belongs

Returns:

the initial state of the new Automaton

Throws:

SchemaException - if XSD constraints are violated

UnresolvedReferenceException - if unresolved references in the schema are found

display

public void display(Logger err)

Display the finite state machine. This is a diagnostic method for internal use.

Parameters:

err - the output destination

subsumesMachine

public static String subsumesMachine(FiniteStateMachine base,
                     FiniteStateMachine sub,
                     SchemaCompiler compiler)

Test whether one finite state machine subsumes another FSM: that is, whether for each path through the second FSM, there is a corresponding path through the first FSM. The algorithm used is as published by Thompson and Tobin, XML Europe 2003.

Parameters:

base - the first FSM (representing the base type)

sub - the other FSM (representing the type that is derived by restriction, validly or otherwise)

compiler - used for error reporting

Returns:

null indicating that the first machine does indeed subsume the other; or a string indicating why it doesn't.

determinize

public static FiniteStateMachine determinize(SchemaCompiler compiler,
                             FiniteStateMachine nfsa)
                                      throws SchemaException

Determinize the finite state machine: that is, ensure that there are no ambiguous transitions from this state. When presented with an input token, the FSA can then examine the specific transitions from this state and either choose one of them, or throw an error.

This is a revised implementation, based more closely on Aho and Ullman p93, to try to eliminate the rare problems that occur when a state has two transitions for the same symbol. (Given UPA, this should occur only with nested loops, e.g. (a{10,11}){1,3} which allows a sequence of 10, 20, 30, 11, 22, or 33 a's.)

Parameters:

compiler - the schema compiler

nfsa - the finite state machine to be determinized

Returns:

the new deterministic finite state machine

Throws:

SchemaException - if an XSD constraint is violated

getOpenContentWildcard

public Wildcard getOpenContentWildcard()

Get the open content wildcard, if any

Returns:

the open content wildcard for this finite state machine, if one is defined

isOpenContentInterleaved

public boolean isOpenContentInterleaved()

Ask whether the open content wildcard for this finite state machine (assuming there is one) permits interleaved content (as opposed to suffixed content only)

Returns:

true if the open content wildcard permits interleaved content.

serialize

public void serialize(SchemaModelSerializer serializer)
               throws XPathException

Output a reppresentation of this finite state machine

Parameters:

serializer - the schema model serializer to which this representation is to be written

Throws:

XPathException - if any error occurs during serialization