RelEx Semantic Relation Extractor

Version 1.5.2 XXX 2014

RelEx is a syntactic dependency extractor and semantic framing generator; it will parse English language sentences and return the dependency relationships between different parts of the sentence, and also provide semantic framing tags based on syntax and semantic categories.

There are multiple inter-related parts to RelEx. The core component extracts the dependency relationships. Additional parts perform functions such as anaphora resolution, provide semantic frame output, provide output in various formats, including one format suitable for later batch post-processing, another format suitable for input to OpenCog, and an W3C OWL format. There are also a small assortment of perl scripts for cleaning up web and wiki pages, &c.

The main RelEx website is at

http://opencog.org/wiki/RelEx

It provides an overview of the project, as well as detailed documentation.

The source code management system is at

http://github.com/opencog/relex

Source tarballs may be downloaded from either of two locations:

https://launchpad.net/relex/+download http://www.abisource.com/downloads/link-grammar/relex/

Build and install of the core package is discussed below.

Dependencies

Installing on Ubuntu/Debian

An installation script for Ubuntu/Debian is provided in the install-scripts directory.

Install and run via Docker

This distrubution includes a Dockerfile for easy use with Docker (http://www.docker.io). To use this, simply say:

$ docker build -t test/relex . $ docker run -i -t -p :3333 -w /home/Downloads/relex mine/relex /bin/sh plain-text-server.sh

or

$ docker run -i -t -p :4444 -w /home/Downloads/relex mine/relex /bin/sh opencog-server.sh $ docker run -i -t -p :9000 -w /home/Downloads/relex mine/relex /bin/sh link-grammar-server.sh

Installing on all other systems

For other systems, follow the instructions below. To build and use RelEx, the following packages are required to be installed:

• libgetopt-java (GNU getopt)
• Link Parser
• WordNet 3.0
• JWNL Java wordnet library
• OpenNLP tools (optional)
• W3C OWL (optional)

Pre-requisite dependencies

The following packages are required pre-requisites for building RelEx.

• Link Grammar Parser Compile and install the Link Grammar Parser. This parser is described at

  http://www.link.cs.cmu.edu/link/

  and sources are available for download at

  http://www.abisource.com/projects/link-grammar/#download

  Link-grammar version 5.0.0 or later is needed to obtain a variety of required fixes.

  The Link Grammar Parser is the underlying engine, providing the core sentence parsing ability.

  If the parser is not installed in the default location, be sure to modify -Djava.library.path appropriately in relation-extractor.sh and other shell scripts.

• GNU getopt This is a standard command-line option parsing library. For Ubuntu, install the libgetopt-java package.

• Wordnet Wordnet is used by RelEx to provide basic English morphology analysis, such as singular versions of (plural) nouns, base forms (lemmas) of adjectives, adverbs and infinitive forms of verbs.

  Download, unpack and install WordNet 3.0. The install directory needs to be specified in data/wordnet/file_properties.xml, with the name="dictionary_path" property in this file.

  Some typical install locations are:

  • /opt/WordNet-3.0/data for RedHat and SuSE
  • /usr/share/wordnet for Ubuntu and Debian
  • C:\Program Files\WordNet\3.0\data for Windows

  The relex/Morphy/Morphy.java class provides a simple, easy-to-use wrapper around wordnet, providing the needed word morphology info.

• didion.jwnl The didion JWNL is the "Java WordNet Library", and provides the Java programming API to access the wordnet data files. Its home page is at

  http://sourceforge.net/projects/jwordnet

  and can be downloaded from

  http://sourceforge.net/project/showfiles.php?group_id=33824

  Verify that the final installed location of jwnl.jar is correctly specified in the build.xml file. Note that GATE also provides a jwnl.jar, but the GATE version of jwnl.jar is not compatible (welcome to java DLL hell).

  When copying jwnl.jar: verify the file permisions! Be sure to issue the following command: chmod 644 jwnl.jar, as otherwise, you'll get strange "java cannot unzip jar" error messages.

• Apache commons logging The JWNL package requires that the Apache commons logging jar file be installed. In Debian/Ubuntu, this is supplied by the libcommons-logging-java package. In RedHat/CentOS systems, the package name is jakarta-commons-logging.

Optional packages

The following packages are optional. If they are found, then additional parts of RelEx will be built, enabling additional function.

• OpenNLP RelEx uses OpenNLP for sentence detection, giving RelEx the ability to find sentence boundaries in free text. If OpenNLP is not found, then the less accurate java.text.BreakIterator class is used.

  The OpenNLP home page is at

  http://opennlp.sourceforge.net/ Download and install OpenNLP tools, and verify that the installed files are correctly identified in both build.xml and in relation-extractor.sh.

  OpenNLP also requires the installation of maxent from

  http://maxent.sourceforge.net/

  You'll need maxent-3.0.0.jar and opennlp-tools-1.5.0.jar.

  The OpenNLP package is used solely in corpus/DocSplitter.java, which provides a simple, easy-to-use wrapper for splitting a document into sentences. Replace this file if an alternate sentence detector is desired.

• Trove Some users may require the GNU Trove to enable OpenNLP, although this depends on the JDK installed. GNU Trove is an implementation of the java.util class hierarchy, which may or may not be included in the installed JDK. If needed, download trove from:

  > http://trove4j.sourceforge.net/
  

  Since trove is optimized, using it may improve performance and/or decrease memory usage, as compared to the standard Sun JDK implementation of the java.util hierarchy.

  IMPORTANT OpenNLP expects Gnu Trove version 1.0, and will not work with version 2.0 !!

• xercesImpl.jar Older versions of the OpenNLP package require that the Xerces2 XML parser package be installed. In Debian/Ubunutu, this is supplied by the libxerces2-java package.

Building

After the above are installed, the relex java code can be built. The build system uses ant, and the ant build specifications are in build.xml. Simply saying ant at the command line should be enough to build. Saying ant run will run a basic demo of the system. The ant test command will run several tests verifying both regular parsing, and the Stanford-parser compatibility mode.

Using RelEx

It is assumed that RelEx will be used in one of two different ways. These are in a "batch processing" mode, and a "custom Java development" mode.

In the "batch processing mode", RelEx is run once over a large text, and its output is saved to a file. This output can then be post-processed at a later time, to extract desired info. The goal here is to avoid the heavy CPU overhead of re-parsing a large text over and over. Example post-processing scripts are included (described below).

In the "custom Java development" mode, it is assumed that a capable Java programmer can write new code to interface RelEx to meet their needs. A good place to start is to review the workings of the output code in src/java/relex/output/*.java.

The standard RelEx demo output is NOT SUITABLE for post-processing. It is meant to be a human-readable example of what the system generates; it does not include all required output. For example, if the same word appears in a sentence twice, the demo output will not distinguish between these two words.

This release of RelEx includes an experimental Stanford-parser compatibility mode. In this mode, RelEx will generate the same dependency relations as the Stanford parser. This mode is technically interesting for comparing output; RelEx is more than three time faster than the lexicalized (factored) Stanford parser, although it is slower than the PCFG parser. This is described in greater detail in the file README-Stanford.

This release of RelEx includes an optional Penn Treebank style part of speech tagger. The tagger is experimental, and has not been evaluated for accuracy. It is probable that the accuracy is low, primarily because it has not been well tested. Because the tagging is based on the syntactic parse, in principle the accuracy could be very high, once fully debugged.

Running RelEx

Several example unix shell scripts and MS Windows batch files are included to show sample usage. These files (*.sh in unix, or *.bat, in Windows) define the required system properties, classpath and JVM options.

If there are any ClassNotFound exceptions, please verify the paths and values in these files.

relation-extractor.sh

The primary usage example is the relation-extractor.sh file. Running this will display:

• The link parser output.
• The detected persons, organizations and locations.
• The dependency relations found.
• Anaphora resolutions.
• Parse ranking info.
• (Optionally) Stanford and Penn Treebank output.

Output is controlled by command-line flags that are set in the shell script. The -h flag will print a list of all of the available command-line options.

batch-process.sh

The batch-process.sh script is an example batch processing script. This script outputs the so-called "compact (cff) format" which captures the full range of Link Grammar and RelEx output in a format that can be easily post-processed by other systems (typically by using regex's).

The idea behind the batch processing is that it is costly to parse large quantities of text: thus, it is convenient to parse the text once, save the results, and then perform post-processing at leisure, as needed. Thus, the form of post-processing can be changed at will, without requiring texts to be re-processed over and over again.

src/perl/cff-to-opencog.pl

This perl script provides an example of post-processing: it converts the "cff" batch output format into OpenCog hypergraphs, which can then be processed by OpenCog.

opencog-server.sh

This script starts a relex server that listens for plain-text input (English sentences) on port 4444. It then parses the text, and returns opencog output on the same socket. This server is meant to serve the OpenCog chatbot directly; it is not intended for general, manual use.

doc-splitter.sh

The doc-splitter.sh file is a simple command-line utility to reformat a free-form text into sentences, one per line.

src/perl/wiki-scrub.pl

Ad-hoc script to scrub Wikipedia xml dumps, outputting only valid English-language sentences. This script removes wiki markup, URL's tables, images, & etc. It currently seems to be pretty darned bullet-proof, although it might handle multi-line refs incorrectly.

Using RelEx in custom code

The primary output of RelEx is the set of semantic relationships of a sentence. To obtain the list of these relationships, make a copy of src/java/relex/output/SimpleView.java, and customize it to provide the relationships that you wish, in the format that you wish.

The class src/java/relex/RelationExtractor.java should be considered to be a large example program illustrating all of the various features of RelEx. For custom applications, this class should be copied and modified as desired to fit the application.

Speed test results

Performance comparison of RelEx-1.2.0 vs. Stanford-1.6.1, run 11 Oct 2009. Test corpus: first 150 sentences (including preface boilerplate) from Project Gutenberg "Pride and Prejudice". Due to differences in sentence detection, Stanford and RelEx disagree on the sentence count. Due to differences in counting punctuation, the splitting of possessives and contractions, the two disagree on the word count as well.

Since these tests were run, the performance of link-grammar has been improved by a factor of 2x-3x. This update should have a significant effect on relex speeds.

The unix command wc counts 2609 words in 148 sentences, for 2609/148 = 17.6 words/sent.

Stanford, w/ englishFactored.ser.gz , w/unix time command:

  real	10m4.882s
  user	10m1.974s
  sys	0m4.208s

Actual: 2609/605= 4.31 words/sec

Stanford, w/ englishPCFG.ser.gz , w/unix time command:

  real	2m21.690s
  user	2m23.165s
  sys	0m1.056s

Actual: 2609/143 = 18.24 words/sec

Stanford, w/ wsjFactored.ser.gz , w/unix time command:

  real	10m5.972s
  user	10m3.802s
  sys	0m4.516s

Stanford, w/ wsjPCFG.ser.gz , w/unix time command:

  real	2m11.154s
  user	2m14.312s
  sys	0m1.144s

Actual: 2609/134 = 19.47 words/sec

RelEx, w/unix time command:

  real	2m59.739s
  user	2m36.342s
  sys	0m22.137s

Actual: 2609/180 = 14.50 words/sec

  Ratio: Stanford-englishFactored/RelEx = 605sec/180sc = 3.36x (faster)
  Ratio: Stanford-wsjFactored/RelEx = 606sec/180sec = 3.36x (faster)
  Ratio: Stanford-englishPCFG/RelEx = 143sec/180sec = 0.79x (slower)
  Ratio: Stanford-wsjPCFG/RelEx = 134sec/180sec = 0.74x (slower)

TODO

TODO - LinkGraphGenerator

This graph visualization class is not currently used. It should be wired up and turned on.

TODO - OpenNLP

A new version of OpenNLP is available. It is not backwards-compatible with the OLD API. Need to port relex to the new API.

TODO - Comparatives

RelEx is pretty broken when it comes to handling comparative sentences. This needs fixing.

TODO - Java Install

The Java install dependencies would be much easier to deal with if there was a centralized repository from which one could easily obtain the needed jar files. That is, something analogous to apt-get or CPAN. The closest such thing for Java is maven; however, none of the jar files required by relex have been checked into maven. Thus, a to-do: get all of the jar files submitted to maven.

TODO - Wordnet Install

Windows users consistently have trouble installing Wordnet correctly. In particular, dictionary location appears to be totally random. Try to find some work-around for this.

TODO - polywords, lexical units, collocations, idioms.

Would be nice to identify: "By the way" as a polyword. "Break a leg" as an idiom.

Bugs

Sentence splitter: The sentence splitter fails to split the following:

"In such cases, a woman has not often much beauty to think of." "But, my dear, you must indeed go and see Mr. Bingley when he comes into the neighbourhood."

todo

• write paper on question normalization including %atLocation
• write paper on wsd by pos-lookup
• write paper on relex overview