Author: buildbot
Date: Thu Sep 22 14:54:15 2011
New Revision: 796106
Log:
Staging update by buildbot
Added:
websites/staging/stanbol/trunk/content/stanbol/docs/trunk/enhancer/engines/keywordlinkingengine.mdtxt
Modified:
websites/staging/stanbol/trunk/content/stanbol/docs/trunk/engines.html
Modified: websites/staging/stanbol/trunk/content/stanbol/docs/trunk/engines.html
==============================================================================
--- websites/staging/stanbol/trunk/content/stanbol/docs/trunk/engines.html
(original)
+++ websites/staging/stanbol/trunk/content/stanbol/docs/trunk/engines.html Thu
Sep 22 14:54:15 2011
@@ -68,7 +68,15 @@
</ul>
</li>
<li>
-<p><strong>Taxonomy Linking Engine</strong></p>
+<p><strong><a
href="engines/keywordlinkingengine.html">KeywordLinkingEngine</a></strong></p>
+<ul>
+<li>NLP processing using OpenNLP</li>
+<li>supports multiple languages</li>
+<li>dedect occurences of untyped entities as concepts, takes local taxonomies
as linking target</li>
+</ul>
+</li>
+<li>
+<p><em>Taxonomy Linking Engine</em> (deprecated, see KeywordLinkingEngine)</p>
<ul>
<li>NLP processing using OpenNLP POS</li>
<li>detect occurrences of untyped entities as concepts, takes local taxonomies
as linking target</li>
Added:
websites/staging/stanbol/trunk/content/stanbol/docs/trunk/enhancer/engines/keywordlinkingengine.mdtxt
==============================================================================
---
websites/staging/stanbol/trunk/content/stanbol/docs/trunk/enhancer/engines/keywordlinkingengine.mdtxt
(added)
+++
websites/staging/stanbol/trunk/content/stanbol/docs/trunk/enhancer/engines/keywordlinkingengine.mdtxt
Thu Sep 22 14:54:15 2011
@@ -0,0 +1,119 @@
+Title: The Keyword Linking Engine: custom vocabularies and multiple languages
+
+The
[KeywordLinkingEngine](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/)
is a re-implementation of the
[TaxonomyLinkingEngine](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/taxonomylinking/)
that is more modular and therefore better suited for future improvements and
extensions as requested by
[STANBOL-303](https://issues.apache.org/jira/browse/STANBOL-303). Its main
improvements are its ability to support multiple languages and provide
enhancement results specific to custom vocabulary.
+
+
+## Multiple Language Support ##
+
+The KeywordLinkingEngine supports multiple languages. However, the performance
and to some extend also the quality of the enhancements for a specific language
is depended on the following:
+
+* **Language detection:** The KeywordLinkingEngine depends on the correct
detection of the language by the LanguageIdentificationEngine. If no language
is detected or this information is missing then "English" is assumed as default.
+* **Multi-lingual labels of the controlled vocabulary:** 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.
+* **Natural Language Processing support:** The KeywordLinkingEngine is able to
use [Sentence
Detectors](http://opennlp.sourceforge.net/api/opennlp/tools/sentdetect/SentenceDetector.html),
[POS (Part of Speech)
taggers](http://opennlp.sourceforge.net/api/opennlp/tools/postag/POSTagger.html)
and
[Chunkers](http://opennlp.sourceforge.net/api/opennlp/tools/chunker/Chunker.html).
If such components are available for a language then they are used to optimize
the enhancement process.
+
+ **Sentence detector:** 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 entire content is treated as a single sentence.
+
+ **Tokenizer:** A (word)
[tokenizer](http://opennlp.sourceforge.net/api/opennlp/tools/tokenize/Tokenizer.html)
is required. If no tokenizer is available for a given language, then the
[OpenNLP
SimpleTokenizer](http://opennlp.sourceforge.net/api/opennlp/tools/tokenize/SimpleTokenizer.html)
is used as default.
+
+ **POS tagger:** POS taggers annotate tokens with their type. Because of the
KeywordLinkingEngine is only interested in Nouns, Foreign Words and Numbers,
the presence of such a 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.
+
+ **Chunker:** There are two types of Chunkers. First the
[Chunkers](http://opennlp.sourceforge.net/api/opennlp/tools/chunker/Chunker.html)
as provided by OpenNLP (based on statistical models) and second a [POS tag
based
Chunker](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/commons/opennlp/src/main/java/org/apache/stanbol/commons/opennlp/PosTypeChunker.java)
provided by the openNLP bundle of Stanbol. Currently the availability of a
Chunker does not have a big influence on the performance nor the quality of the
Enhancements.
+
+* **Configuration:** The set of languages to be annotated can be configured
for the KeywordLinkingEngine. An empty configuration indicates that texts in
any language should be processed. By using this configuration it is possible to
configure different KeywordLinkingEngine instances for different languages
(e.g. with different configurations)
+
+## Keyword extraction and linking workflow ##
+
+Basically the text is parsed from the beginning to the end and words are
looked up in the configured controlled vocabulary.
+
+### Text Processing ###
+
+The
[AnalysedContent](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/AnalysedContent.java)
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
[TextAnalyzer](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/commons/opennlp/src/main/java/org/apache/stanbol/commons/opennlp/TextAnalyzer.java)
utility. In general this part is still very focused on OpenNLP. Making it also
usable together with other NLP frameworks would probably need some re-factoring.
+
+The current state of the processing is represented by the
[ProcessingState](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/impl/ProcessingState.java).
Based on the capabilities of the NLP framework for the current language it
provides a the following set of information:
+
+* **AnalysedSentence:** If a sentence detector is present, than this represent
the current sentence of the text. If not, then the whole text is represented as
a single sentence. The AnalysedSentence also provides access to POS tags and
Chunks (if available)
+* **Chunk:** If a chunker is present, then this represents the current chunk.
Otherwise this will be null.
+* **Token:** The currently processed word part of the chunk and the sentence.
+* **TokenIndex:** The index of the currently active token relative to the
AnalysedSentence.
+
+The ProcessingState provides means to navigate to the next token. If chunks
are present tokens that are outside of chunks are ignored.
+
+### Entity Lookup ###
+
+A "OR" query with [1..MAX_SEARCH_TOKENS] tokens is used to lookup entities via
the
[EntitySearcher](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntitySearcher.java)
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
([EntityhubSearcher](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))
and (2) for ReferencedSites
([ReferencedSiteSearcher](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)).
There is also an
[Implementation](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/test/java/org/apache/stanbol/enhancer/engines/keywordextraction/impl/TestSearcherImpl.java)
that holds entities in-memory, however currently this is only used for unit
tests.
+
+Queries do use the configured
[EntityLinkerConfig](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java).getNameField()
and the language of labels is restricted to the current language or labels
that do not define any language.
+
+Only "processable" tokens are used to lookup entities. If a token is
processable is determined as follows:
+
+* If POS tags are available the "Boolean processPOS(String posTag)" method of
the
[AnalysedContent](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/AnalysedContent.java)
is used to check if a Token needs to be processed.
+* If this method returns NULL or no POS tags are available, then all Tokens
longer than
[EntityLinkerConfig](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java).getMinSearchTokenLength()
(default=3) are considered as processable.
+
+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.
+
+### Matching of found Entities: ###
+
+All labels (values of the
[EntityLinkerConfig](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java).getNameField()
field) in the language of the content or without any defined language are
candidates for matches.
+
+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:
+
+* All tokens (of the text) following the current position are searched within
the label.
+* As of now, tokens MUST appear in the correct order within a label (e.g.
"Murdoch Rupert" will NOT match "Rupert Murdoch")
+* 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)
+* 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")
+
+Entities are
[Suggested](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/Suggestion.java)
if:
+
+* a label does match exactly with the text following the current position it
the entity is suggested. (e.g.
[Passerine](http://en.wikipedia.org/wiki/Passerine))
+* a label matches at least
[EntityLinkerConfig](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java).getMinFoundTokens()
(default=2) are matching with the text. This ensures that "[Rupert
Murdoch](http://en.wikipedia.org/wiki/Rupert_Murdoch)" is not suggested for
"[Rupert](http://en.wikipedia.org/wiki/Rupert)" but on the other hand "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".
+
+The described matching process is currently directly part of the
[EntityLinker](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinker.java).
To support different matching strategies this would need to be externalized
into an own "EntityLabelMatcher" interface.
+
+### Processing of Entity Suggestions ###
+
+In case there are one or more
[Suggestion](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/Suggestion.java)s
of Entities for the current position within the text a
[LinkedEntity](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/LinkedEntity.java)
instance is created.
+
+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.
+
+TextAnnotations as defined in the [Stanbol Enhancement
Structure](http://wiki.iks-project.eu/index.php/EnhancementStructure) do use
the [dc:type](http://www.dublincore.org/documents/dcmi-terms/#terms-type)
property to provide the general type of the extracted Entity. However suggested
Entities might have very specific types. Therefore the
[EntityLinkerConfig](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java)
provides the possibility to map the specific types of the Entity to types used
for the dc:type property of TextAnnotations. The
[EntityLinkerConfig](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinkerConfig.java).DEFAULT_ENTITY_TYPE_MAPPINGS
contains some predefined mappings.
+*Note that the 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".*
+
+In some cases suggested entities might redirect to others. In the case of
Wikipedia/DBpedia this is often used to link from acronyms like
[IMF](http://en.wikipedia.org/w/index.php?title=IMF&redirect=no) to the real
entity [International Monetary
Fund](http://en.wikipedia.org/wiki/International_Monetary_Fund). But also some
Thesauri 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 KeywordLinkingEngine 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 replaced with the first redirected entity.
+
+### Confidence for Suggestions ###
+
+The confidence for suggestions is calculated based on the following algorithm:
+
+Input Parameters
+
+* max_matched: maximum number of the matched tokens of all suggestions e.g.
the text contains "Barack Obama" -> 2
+* matched: number of tokens that match for the current suggestion e.g. "Barack
Hussein Obama" -> 2
+* span: number of tokens selected by the current suggestion e.g. "Barack
Hussein Obama" -> 2
+* label_tokens: number of tokens of the matched label of the current entity
(label_token) e.g. "Barack Hussein Obama" -> 3
+
+confidence = (match/max_matched)^2 * (matched/span) * (matched/label_tokens)
+
+Some Examples:
+
+* "Barack Hussein Obama" matched against the text "Barack Obama" results in a
confidence of (2/2)^2 * (2/2) * (2/3) = 0,67
+* "University Michigan" matched against the text "University of Michigan"
results in a confidence of (2/2)^2 * (2/3) * (2/2) = 0,67
+* "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.
+
+The calculation of the confidence is currently direct part of the
[EntityLinker](http://svn.apache.org/repos/asf/incubator/stanbol/trunk/enhancer/engines/keywordextraction/src/main/java/org/apache/stanbol/enhancer/engines/keywordextraction/linking/EntityLinker.java).
To support different matching strategies this would need to be externalized
into an own interface.
+
+## Future Plans for the TaxonomyLinkingEngine ##
+
+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 KeywordLinkingEngine.
+
+In the future it is planed to repurpose the TaxonomyLinkingEngine as a special
version of the KeywordLinkingEngine with a specialized configuration and
feature set targeted for (hierarchical) Taxonomies.
+
+This will include:
+
+* default configuration specific for SKOS
+* support for term hierarchies - adding suggestions for parent concepts
+* 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.
+
+
