Author: buildbot
Date: Thu Sep 22 12:35:28 2011
New Revision: 796103
Log:
Staging update by buildbot
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websites/staging/stanbol/trunk/content/stanbol/docs/trunk/enhancer/engines/keywordextractionengine.html
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websites/staging/stanbol/trunk/content/stanbol/docs/trunk/enhancer/engines/keywordextractionengine.html
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+ <h1 class="title"></h1>
+ <h1 id="keywordextractionengine">KeywordExtractionEngine</h1>
+<p>The <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/";>KeywordExtractionEngine</a>
is a re-implementation of the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/taxonomylinking/";>TaxonomyLinkingEngine</a>
that is more modular and therefore better suited for future improvements and
extensions as requested by <a
href="https://issues.apache.org/jira/browse/STANBOL-303";>STANBOL-303</a>.</p>
+<h2 id="multiple_language_support">Multiple Language Support</h2>
+<p>The KeywordExtractionEngine can supports multiple languages. However the
performance and to some extend also the quality of the enhancements are
depended on the following parameters</p>
+<ul>
+<li><strong>Language detection:</strong> The KexwordExtractionEngine depends
on the correct detection of the language by the LangIdEnhancementEngine. If no
language was detected or this information is missing than "English" is assumed
as default.</li>
+<li><strong>Multi-Lingual labels of the Controlled Vocabulary:</strong>
Occurrences are searched within labels of the current Language and labels
without any defined language. e.g. English labels will not be matched against
German language texts.</li>
+<li><strong>Natural Language Processing support:</strong> The
KexwordExtractionEngine is able to use <a
href="http://opennlp.sourceforge.net/api/opennlp/tools/sentdetect/SentenceDetector.html";>Sentence
Detectors</a>, <a
href="http://opennlp.sourceforge.net/api/opennlp/tools/postag/POSTagger.html";>POS
(Part of Speech) taggers</a> and <a
href="http://opennlp.sourceforge.net/api/opennlp/tools/chunker/Chunker.html";>Chunkers</a>.
If such components are available for a language the they are used to optimize
the enhancement process.</li>
+</ul>
+<p><strong>Sentence detector:</strong> If a sentence detector is present the
memory footprint of the engines improves, because Tokens, POS tags and Chunks
are only kept for the currently active sentence. If no sentence detector is
available the whole content is treated as a single Sentence.</p>
+<p><strong>Tokenizer:</strong> A (word) <a
href="http://opennlp.sourceforge.net/api/opennlp/tools/tokenize/Tokenizer.html";>tokenizer</a>
is required. If no tokenizer is available for a given language, than the <a
href="http://opennlp.sourceforge.net/api/opennlp/tools/tokenize/SimpleTokenizer.html";>OpenNLP
SimpleTokenizer</a> is used as default.</p>
+<p><strong>POS tagger:</strong> POS taggers annotate tokens with there type.
Because of the KeywordExtractionEngine is only interested in Nouns, Foreign
Words and Numbers the presence of such an tagger allows to skip a lot of the
tokens and to improve performance. However POS taggers use different sets of
tags for different languages. Because of that it is not enough that a POS
tagger is available for a language there MUST BE also a configuration of the
POS tags for that language that need to be processed.</p>
+<p><strong>Chunker:</strong> There are two types of Chunkers. First the <a
href="http://opennlp.sourceforge.net/api/opennlp/tools/chunker/Chunker.html";>Chunkers</a>
as provided by OpenNLP (based on statistical models) and second a <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/commons/opennlp/src/main/java/org/apache/stanbol/commons/opennlp/PosTypeChunker.java";>POS
tag based Chunker</a> provided by the openNLP bundle of Stanbol. Currently the
Availability of a Chunker does not have an big influence on the performance nor
the quality of the Enhancements.</p>
+<ul>
+<li><strong>Configuration:</strong> The set of languages to be annotated can
be configured for the KexwordExtractionEngine. An empty configuration indicates
that texts in any language should be processed. By using this configuration it
is possible to configure different KexwordExtractionEngine instances for
different languages (e.g. with different configurations)</li>
+</ul>
+<h2 id="keyword_extraction_workflow">Keyword extraction workflow</h2>
+<p>Basically the Text is parsed from the beginning to the end and words are
looked up in the configured Controlled Vocabulary.</p>
+<h3 id="text_processing">Text Processing</h3>
+<p>The <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/AnalysedContent.java";>AnalysedContent</a>
Interface is used to access natural language text that was already processed
by an NLP framework. Currently there is only a single implementation based on
the commons.opennlp <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/commons/opennlp/src/main/java/org/apache/stanbol/commons/opennlp/TextAnalyzer.java";>TextAnalyzer</a>
utility. In general this part is still very focused on OpenNLP. Making it also
usable together with other NLP frameworks would probably need a lot of
refactoring.</p>
+<p>The current state of the processing is represented by the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/impl/ProcessingState.java";>ProcessingState</a>.
Based on the capabilities of the NLP framework for the current language it
provides a different set of information:</p>
+<ul>
+<li><strong>AnalysedSentence:</strong> If a sentence detector is present, than
this represent the current sentence of the text. If not, than the whole text is
represented as a single sentence. The AnalysedSentence also provides access to
POS tags, Chunks (if available)</li>
+<li><strong>Chunk:</strong> If a chunkier is present, than this represents the
current chunk. Otherwise this will be null </li>
+<li><strong>Token:</strong> The currently processed word part of the chunk and
the sentence</li>
+<li><strong>TokenIndex:</strong> The index of the currently active token
relative to the AnalysedSentence.</li>
+</ul>
+<p>The ProcessingState provides means to navigate to the next token. If chunks
are present tokens that are outside of chunks are ignored.</p>
+<h3 id="entity_lookup">Entity Lookup</h3>
+<p>A "OR" query with [1..MAX_SEARCH_TOKENS] tokens is used to lookup entities
via the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntitySearcher.java";>EntitySearcher</a>
interface. If the actual implementation cut off results, than it must be
ensured that Entities that match both tokens are ranked first.
+Currently there are two implementations of this interface (1) for the
Entityhub (<a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/impl/EntityhubSearcher.java";>EntityhubSearcher</a>)
and (2) for ReferencedSitess (<a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/impl/ReferencedSiteSearcher.java";>ReferencedSiteSearcher</a>).
There is also an <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/test/java/org/apache/stanbol/enhancer/engines/keywordextraction/impl/TestSearcherImpl.java";>Implementation</a>
that holds entities in-memory, however currently this is only used for unit
tests.</p>
+<p>Queries do use the configured <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java";>EntityLinkerConfig</a>.getNameField()
and the language of labels is restricted to the current language or labels
that do not define any language.</p>
+<p>Only "processable" Tokens are used to lookup entities. If a Token is
processable is determined as follows:</p>
+<ul>
+<li>If POS tags are available the "Boolean processPOS(String posTag)" method
of the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/AnalysedContent.java";>AnalysedContent</a>
is used to check if a Token needs to be processed.</li>
+<li>If this method returns NULL or no POS tags are available, than all Tokens
with equals or more Chars than <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java";>EntityLinkerConfig</a>.getMinSearchTokenLength()
(default=3) are considered as processable.</li>
+</ul>
+<p>Typically the next MAX_SEARCH_TOKENS processable tokens are used for a
lookup. However the current Chunk/Sentence is never left in the search for
processable tokens.</p>
+<h3 id="matching_of_found_entities">Matching of found Entities:</h3>
+<p>All labels (values of the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java";>EntityLinkerConfig</a>.getNameField()
field) in the language of the content or without any defined language are
candidates for matches.</p>
+<p>For each label that fulfills the above criteria the following steps are
processed. The best result is used as the result of the whole matching
process:</p>
+<ul>
+<li>All tokens (of the text) following the current position are searched
within the label.</li>
+<li>As of now, tokens MUST appear in the correct order within a label (e.g.
"Murdoch Rupert" will NOT match "Rupert Murdoch")</li>
+<li>On the first processable token of the text that is not present within the
label matching is canceled. (see the definition of processable token above)</li>
+<li>On the second non-processable token not found in the label the matching is
also canceled (e.g. "University of Michigan" will match "University
Michigan")</li>
+</ul>
+<p>Entities are <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/Suggestion.java";>Suggested</a>
if:</p>
+<ul>
+<li>a label does matches exactly with the text following the current position
it the entity is suggested. (e.g. <a
href="http://en.wikipedia.org/wiki/Passerine";>Passerine</a>)</li>
+<li>a label matches at least <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java";>EntityLinkerConfig</a>.getMinFoundTokens()
(default=2) are matching with the text. This ensures that "<a
href="http://en.wikipedia.org/wiki/Rupert_Murdoch";>Rupert Murdoch</a>" is not
suggested for "<a href="http://en.wikipedia.org/wiki/Rupert";>Rupert</a>" but
ensures that "Barack Hussein Obama" is suggested for "Barack Obama". Setting
"minFoundToken" to values less than two will usually cause a lot of false
positives, but would also come up with a suggestion for "Barack Obama" if the
content contains the word "Obama".</li>
+</ul>
+<p>The described matching process is currently directly part of the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinker.java";>EntityLinker</a>.
To support different matching strategies this would need to be externalized
into an own "EntityLabelMatcher" interface.</p>
+<h3 id="processing_of_entity_suggestions">Processing of Entity Suggestions</h3>
+<p>In case there are one or more <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/Suggestion.java";>Suggestion</a>s
of Entities for the current position within the text a <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/LinkedEntity.java";>LinkedEntity</a>
instance is created.</p>
+<p>LinkedEntity is an object model representing the Stanbol Enhancement
Structure. After the processing of the parsed content is completed the
LinkedEntities are "serialized" as RDF triples to the metadata of the
ContentItem.</p>
+<p>TextAnnotations as defined in the <a
href="http://wiki.iks-project.eu/index.php/EnhancementStructure";>Stanbol
Enhancement Structure</a> do use the <a
href="http://www.dublincore.org/documents/dcmi-terms/#terms-type";>dc:type</a>
property to provide the general type of the extracted Entity. However suggested
Entities might have very specific types. Therefore the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java";>EntityLinkerConfig</a>
provides the possibility to map the specific types of the Entity to types used
for the dc:type property of TextAnnotations. The <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java";>EntityLinkerConfig</a>.DEFAULT_ENTITY_TYPE_MAPPINGS
contains some pred
efined mappings.
+Note that field used to retrieve the types of an suggested Entity can be
configured by the EntityLinkerConfig. The default value for the type field is
"rdf:type".</p>
+<p>In some cases suggested entities might redirect to others. In the case of
Wikipedia/DBpedia this is often used to link from acronyms like <a
href="http://en.wikipedia.org/w/index.php?title=IMF&redirect=no";>IMF</a> to
the real entity <a
href="http://en.wikipedia.org/wiki/International_Monetary_Fund";>International
Monetary Fund</a>. But also some Thesaurus define labels as own Entities with
an URI and users might want to use the URI of the Concept rather than one of
the label.
+To support such use cases the KeywordExtractionEngine has support for
redirects. Users can first configure the redirect mode (ignore, copy values,
follow) and secondly the field used to search for redirects
(default=rdfs:seeAlso).
+If the redirect mode != ignore for each suggestion the Entities referenced by
the configured redirect field are retrieved. In case of the copy values mode
the values of the name, and type field are copied. In case of the follow mode
the suggested entity is repressed with the first redirected entity.</p>
+<h3 id="confidence_for_suggestions">Confidence for Suggestions</h3>
+<p>The confidence for suggestions is calculated based on the following
algorithm:</p>
+<p>Input Parameters</p>
+<ul>
+<li>max_matched: maximum number of the matched tokens of all suggestions e.g.
the text contains "Barack Obama" -> 2</li>
+<li>matched: number of tokens that match for the current suggestion e.g.
"Barack Hussein Obama" -> 2</li>
+<li>span: number of tokens selected by the current suggestion e.g. "Barack
Hussein Obama" -> 2</li>
+<li>label_tokens: number of tokens of the matched label of the current entity
(label_token) e.g. "Barack Hussein Obama" -> 3</li>
+</ul>
+<p>confidence = (match/max_matched)^2 * (matched/span) *
(matched/label_tokens)</p>
+<p>Some Examples:</p>
+<ul>
+<li>"Barack Hussein Obama" matched against the text "Barack Obama" results in
a confidence of (2/2)^2 * (2/2) * (2/3) = 0,67 </li>
+<li>"University Michigan" matched against the text "University of Michigan"
results in a confidence of (2/2)^2 * (2/3) * (2/2) = 0,67</li>
+<li>"New York City" matched against the text "New York Rangers" - assuming
that "New York Rangers" is the best match - results in a confidence of (2/3)^2
* (2/2) * (2/3) = 0,3; Note that the best match "New York Rangers" has
max_matched=3 and gets a confidence of 1.</li>
+</ul>
+<p>The calculation of the confidence is currently direct part of the <a
href="http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinker.java";>EntityLinker</a>.
To support different matching strategies this would need to be externalized
into an own interface.</p>
+<h2 id="future_plans_for_the_taxonomylinkingengine">Future Plans for the
TaxonomyLinkingEngine</h2>
+<p>The TaxonomyLinkingEngine is still available and fully functional. However
it is marked as deprecated and not included in any of the launchers. Current
users are encouraged to switch over to the KeywordExtractionEngine. </p>
+<p>In Future it is planed to repurpose the TaxonomyLinkingEngine as a special
version of the KeywordExtractionEngine with a specialized configuration and
feature set targeted for (hierarchical) Taxonomies.</p>
+<p>This will include: </p>
+<ul>
+<li>default configuration specific for SKOS</li>
+<li>support for term hierarchies - adding suggestions for parent concepts</li>
+<li>support for restricting enhancements to a specific Taxonomy
(skos:ConceptScheme) - this would allow to index several Taxonomies in the same
ReferencedSite but still use only a specific one for the enhancements.</li>
+</ul>
+ </div>
+
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+ <div class="copyright">
+ <p>
+ Copyright © 2010 The Apache Software Foundation, Licensed under
+ the <a href="http://www.apache.org/licenses/LICENSE-2.0";>Apache
License, Version 2.0</a>.
+ <br />
+ Apache, Stanbol and the Apache feather and Stanbol logos are
trademarks of The Apache Software Foundation.
+ </p>
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