org.apache.lucene.util.fst

Class Builder<T>

java.lang.Object

org.apache.lucene.util.fst.Builder<T>

public class Builder<T>
extends Object

Builds a minimal FST (maps an IntsRef term to an arbitrary output) from pre-sorted terms with outputs. The FST becomes an FSA if you use NoOutputs. The FST is written on-the-fly into a compact serialized format byte array, which can be saved to / loaded from a Directory or used directly for traversal. The FST is always finite (no cycles).

NOTE: The algorithm is described at http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.24.3698

The parameterized type T is the output type. See the subclasses of Outputs.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Builder.Arc<T> Expert: holds a pending (seen but not yet serialized) arc.
static class	Builder.FreezeTail<T> Expert: this is invoked by Builder whenever a suffix is serialized.
static class	Builder.UnCompiledNode<T> Expert: holds a pending (seen but not yet serialized) Node.

Constructor Summary

Constructors

Constructor and Description
Builder(FST.INPUT_TYPE inputType, int minSuffixCount1, int minSuffixCount2, boolean doShareSuffix, boolean doShareNonSingletonNodes, int shareMaxTailLength, Outputs<T> outputs, Builder.FreezeTail<T> freezeTail, boolean willPackFST) Instantiates an FST/FSA builder with all the possible tuning and construction tweaks.
Builder(FST.INPUT_TYPE inputType, Outputs<T> outputs) Instantiates an FST/FSA builder without any pruning.

Method Summary

Methods

Modifier and Type	Method and Description
void	add(IntsRef input, T output) It's OK to add the same input twice in a row with different outputs, as long as outputs impls the merge method.
FST<T>	finish() Returns final FST.
int	getMappedStateCount()
long	getTermCount()
int	getTotStateCount()
void	setAllowArrayArcs(boolean b) Pass false to disable the array arc optimization while building the FST; this will make the resulting FST smaller but slower to traverse.

Methods inherited from class java.lang.Object

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

Constructor Detail

Builder

public Builder(FST.INPUT_TYPE inputType,
       Outputs<T> outputs)

Instantiates an FST/FSA builder without any pruning. A shortcut to Builder(FST.INPUT_TYPE, int, int, boolean, boolean, int, Outputs, FreezeTail, boolean) with pruning options turned off.

Builder

public Builder(FST.INPUT_TYPE inputType,
       int minSuffixCount1,
       int minSuffixCount2,
       boolean doShareSuffix,
       boolean doShareNonSingletonNodes,
       int shareMaxTailLength,
       Outputs<T> outputs,
       Builder.FreezeTail<T> freezeTail,
       boolean willPackFST)

Instantiates an FST/FSA builder with all the possible tuning and construction tweaks. Read parameter documentation carefully.

Parameters:

inputType - The input type (transition labels). Can be anything from FST.INPUT_TYPE enumeration. Shorter types will consume less memory. Strings (character sequences) are represented as FST.INPUT_TYPE.BYTE4 (full unicode codepoints).

minSuffixCount1 - If pruning the input graph during construction, this threshold is used for telling if a node is kept or pruned. If transition_count(node) >= minSuffixCount1, the node is kept.

minSuffixCount2 - (Note: only Mike McCandless knows what this one is really doing...)

doShareSuffix - If true, the shared suffixes will be compacted into unique paths. This requires an additional hash map for lookups in memory. Setting this parameter to false creates a single path for all input sequences. This will result in a larger graph, but may require less memory and will speed up construction.

doShareNonSingletonNodes - Only used if doShareSuffix is true. Set this to true to ensure FST is fully minimal, at cost of more CPU and more RAM during building.

shareMaxTailLength - Only used if doShareSuffix is true. Set this to Integer.MAX_VALUE to ensure FST is fully minimal, at cost of more CPU and more RAM during building.

outputs - The output type for each input sequence. Applies only if building an FST. For FSA, use NoOutputs.getSingleton() and NoOutputs.getNoOutput() as the singleton output object.

willPackFST - Pass true if you will pack the FST before saving. This causes the FST to create additional data structures internally to facilitate packing, but it means the resulting FST cannot be saved: it must first be packed using FST.pack(int, int)}.

Method Detail

getTotStateCount

public int getTotStateCount()

getTermCount

public long getTermCount()

getMappedStateCount

public int getMappedStateCount()

setAllowArrayArcs

public void setAllowArrayArcs(boolean b)

Pass false to disable the array arc optimization while building the FST; this will make the resulting FST smaller but slower to traverse.

add

public void add(IntsRef input,
       T output)
         throws IOException

It's OK to add the same input twice in a row with different outputs, as long as outputs impls the merge method.

Throws:

IOException

finish

public FST<T> finish()
              throws IOException

Returns final FST. NOTE: this will return null if nothing is accepted by the FST.

Throws:

IOException