modnlp.idx.database

Class IntOffsetArrayBinding

java.lang.Object

com.sleepycat.bind.tuple.TupleBase<E>

com.sleepycat.bind.tuple.TupleBinding

modnlp.idx.database.IntOffsetArrayBinding

All Implemented Interfaces:

com.sleepycat.bind.EntryBinding

public class IntOffsetArrayBinding
extends com.sleepycat.bind.tuple.TupleBinding

Tuple binding for compressing and storing arrays of Java ints (ordered in ascending order) into a JE database. These ints will typically indicate the difference between a character offset (distance from the beginning of a file) and the preceding offset: | pos_0 | pos_1-pos_0 | pos_2-pos_1 | .... | pos_n - pos_n-1 \ The compression algorithm works as follows:

  for each offset
    if (offset < max_size_of_unsigned_byte)
      store it as unsigned_byte
    else
      store an overflow marker // i.e. an unsigned byte of value 255
      store offset as unsigned_int
      end if
    end for
  

This is a simple enough strategy that typically achieves a 75% compression ratio (w.r.t. storage of absolute positions). Although the algorithm works for any ordered sequence of ints Caveat: we currently make no effort to store offsets greater than the max size of an unsigned_int

See Also:

WordPositionTable

Field Summary

Fields

Modifier and Type	Field and Description
static long	MAXOFFSET_VALUE

Constructor Summary

Constructors

Constructor and Description
IntOffsetArrayBinding()

Method Summary

Methods

Modifier and Type	Method and Description
java.lang.Object	entryToObject(com.sleepycat.bind.tuple.TupleInput ti)
int	getBytesReceived() Get no.
int	getBytesWritten() Get no of bytes actually written into the Object stream so far
double	getCompressionRatio() getCompressionRatio return the compression ratio given by bytesWritten/bytesReceived;
void	objectToEntry(java.lang.Object object, com.sleepycat.bind.tuple.TupleOutput to)

Methods inherited from class com.sleepycat.bind.tuple.TupleBinding

entryToObject, getPrimitiveBinding, objectToEntry

Methods inherited from class com.sleepycat.bind.tuple.TupleBase

entryToInput, getTupleBufferSize, getTupleOutput, inputToEntry, newOutput, newOutput, outputToEntry, setTupleBufferSize

Methods inherited from class java.lang.Object

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

Field Detail

MAXOFFSET_VALUE

public static long MAXOFFSET_VALUE

Constructor Detail

IntOffsetArrayBinding

public IntOffsetArrayBinding()

Method Detail

objectToEntry

public void objectToEntry(java.lang.Object object,
                 com.sleepycat.bind.tuple.TupleOutput to)

Specified by:

objectToEntry in class com.sleepycat.bind.tuple.TupleBinding

entryToObject

public java.lang.Object entryToObject(com.sleepycat.bind.tuple.TupleInput ti)

Specified by:

entryToObject in class com.sleepycat.bind.tuple.TupleBinding

getCompressionRatio

public double getCompressionRatio()

getCompressionRatio return the compression ratio given by bytesWritten/bytesReceived;

Returns:

the ratio of compression of the array passed to objectToEntry() or zero if objectToEntry() hasn't been called.

getBytesReceived

public int getBytesReceived()

Get no. of bytes passed to objectToEntry() so far.

Returns:

an int value

getBytesWritten

public int getBytesWritten()

Get no of bytes actually written into the Object stream so far

Returns:

a int value