Package com.saxonica.ee.schema.fsa

Class FiniteStateMachine

  • public class FiniteStateMachine
extends java.lang.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.

    • 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

      • 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,
                                                   MissingComponentException
        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
        MissingComponentException - 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 java.lang.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 representation 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