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Apache Stanbol - OpenNLP POS Tagging Engine

OpenNLP POS Tagging Engine

POS tagging Engine using the AnalyzedText ContentPart based on the OpenNLP POS tagging functionality.

Consumed information

POS Tagging

POS tags are represented by adding NlpAnnotations#POS_ANNOTATION's to the Tokens of the AnalyzedText content part. As the OpenNLP Tokenizer supports multiple Pos tags/probability suggestions the OpenNLP POS Tagging Engine can add multiple POS annotations to a Token.

POS annotations are added by using the key "stanbol.enhancer.nlp.pos" and are represented by the PosTag class. However typical users will rather use the NlpAnnotations#POS_ANNOTATION to access POS annotations of tokens

//The POS tag with the highest probability
Value<PosTag> posAnnotation = token.getAnnotation(NlpAnnotations.POS_ANNOTATION);
//Get the list of all POS annotations
List<Value<PosTag>> posAnnotations = token.getAnnotations(NlpAnnotations.POS_ANNOTATION);

//Value provides the probability and the PosTag
double prob = posAnnotation.probability();
PosTag pos = posAnnotation.value();
//The string tag as used by the Tokenizer
String tag = pos.getTag();

//POS tags can be mapped to LexicalCategories and Pos types
//so we can check if a Token is a Noun without the need to
//know the POS tags used by the POS tagger of the current language
boolean isNoun = pos.hasCategory(LexicalCategory.Noun);
boolean isProperNoun = pos.hasPos(Pos.ProperNoun);

//but not all PosTags might be mapped so we should check for
boolean mapped = pos.isMapped();

The OpenNLP Pos Tagging engine supports mapped PosTags for the following languages

TODO: Currently the Engine is limited to those TagSets as it is not yet possible to extend this by additional one.

Tokenizing and Sentence Detection Support

The OpenNLP POS Tagging engine implicitly supports tokenizing and sentence detection. That means if the AnalyzedText is not present or does not contain Tokens than this engine will use the OpenNLP Tokenizer to tokenize the text. If no language specific OpenNLP tokenizer model is available, than it will use the SIMPLE_TOKENIZER.

Sentence detection is only done if no Sentences are present in the AnalyzedText AND if a language specific sentence detection model is available.

NOTE: Support for Tokenizing and Sentence Detection is not a replacement for explicitly adding a Tokenizing and Sentence Detection Engine to a Enhancement Chain as this Engine does not guarantee that Tokens or Sentences are added to the AnalyzedText content part. If no POS model is available for a language or a language is not configured to be processed there will be no Tokens nor Sentences added. Chains the relay on Tokens and/or Sentences MUST explicitly include a Tokenizing and Sentence detection engine!


NOTE that the OpenNLP POS Tagging engine provides a default service instance (configuration policy is optional). This instance processes all languages where default POS models are provided by the OpenNLP service. This Engine instance uses the name 'opennlp-pos' and has a service ranking of '-100'.

While this engine supports the default configuration including the name ( and the ranking (service.ranking) the engine also allows to configure processed languages (org.apache.stanbol.enhancer.pos.languages) and a parameter to specify the name of the POS model used for a language.

1. Processed Language Configuraiton:

For the configuration of the processed languages the following syntax is used:


This would configure the Engine to only process German and English texts. It is also possible to explicitly exclude languages


This specifies that all Languages other than French and Italien are processed.

Values can be parsed as Array or Vector. This is done by using the ["elem1","elem2",...] syntax as defined by OSGI ".config" files. As fallback also ',' separated Strings are supported.

The following example shows the two above examples combined to a single configuration.


NOTE that the "processed language" configuration only specifies what languages are considered for processing. If "de" is enabled, but there is no POS model available for that language, than German text will still not be processed. However if there is a POS model for "it" but the "processed language" configuration does not include Italian, than Italian text will NOT be processed.

2. POS model parameter

The OpenNLP POS annotation engine supports the 'model' parameter to explicitly parse the name of the POS model used for a language. POS models are loaded via the Stanbol DataFile provider infrastructure. That means that models can be loaded from the {stanbol-working-dir}/stanbol/datafiles folder.

The syntax for parameters is as follows


So to use the "" for POS tagging German texts one can use a configuration like follows


By default OpenNLP POS models are loaded for the names '{lang}-pos-perceptron.bin' and '{lang}-pos-maxent.bin' to use models with other names users need to use the 'model' parameter as described above.