Contents
- Introduction
- Negation Annotator
	- NegationAnnotator.xml
	- updating negex patterns
- Status Annotator 

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Introduction
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The context annotator provides a mechanism for examining the context of existing annotations, finding 
events of interest in the context, and acting on those events in some way.  The negation and status 
annotators both take advantage of this infrastructure by examining the context of named entities 
(e.g. disorders and findings) to see if they should be considered as negated (e.g. "no chest pain") 
or if their status should be modified (e.g. "myocardial infarction" should have status "history of").  

In fact, the "negation annotator" is really just the context annotator configured to deal with negations.  

Similarly, the "status annotator" is the context annotator configured to identify the status of named entities.  

To better understand the context annotator code you should start by reading the javadocs for the class 
org.apache.ctakes.necontexts.ContextAnnotator.java.  It provides a nice conceptual overview of how the code works.  

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Negation Annotator
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What follows is an explanation of how negation is performed using the context annotator.  

The negation detection annotator is a pattern-based (no maxent models required/used) approach that uses 
finite state machines and is roughly based on the popular Negex algorithm introduced by Wendy Chapman.  

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NegationAnnotator.xml

We will start by examining the descriptor file desc/NegationAnnotator.xml.  Open this file with the Component 
Descriptor Editor.  Select the first tab labeled "Overview" and observe that the analysis engine that is 
specified is org.apache.ctakes.necontexts.ContextAnnotator.  There is no "negation annotator" analysis 
engine - we simply configure the ContextAnnotator for the task.  Next select the tab labeled "Parameter Settings".

We will discuss each setting in turn:
 
 - MaxLeftScopeSize = 10
   The maximum number of annotations that will make up the left-hand side context is ten.  
   Increase or decrease this parameter setting to increase or decrease the left hand side context.
 - MaxRightScopeSize = 10
   The maximum number of annotations that will make up the right-hand side context is ten.  
   Increase or decrease this parameter setting to increase or decrease the right-hand side context.
 - ScopeOrder = LEFT, RIGHT
   The context annotator will look for signs of negation on the left-hand side of a named entity first and then 
   the right-hand side.
 - ContextAnalyzerClass = org.apache.ctakes.necontexts.negation.NegationContextAnalyzer 
   The context analyzer looks at the context (e.g. the 10 words on the left or right of the named entity) and 
   determines if the named entity should be negated.  If it should, then the negation context analyzer will 
   generate a context hit to be consumed by the context hit consumer (see below.)
 - ContextHitConsumerClass = org.apache.ctakes.necontexts.negation.NegationContextHitConsumer
   The context hit consumer handles context hits generated by the context analyzer.  In this case, the negation 
   context hit consumer simply sets the certainty of a named entity to -1 which indicates that it has been negated.
 - WindowAnnotationClass = edu.mayo.bmi.uima.common.type.Sentence
   When the context annotator collects the context annotations for a named entity, it will not look beyond the 
   boundaries of the sentence that the named entity is found in.
 - FocusAnnotationClass = edu.mayo.bmi.uima.common.type.NamedEntity
   The negation annotator is concerned with negating named entities and thus the focus annotation type 
   (the annotations for which a context is generated and examined) specifies named entities.
 - ContextAnnotationClass = edu.mayo.bmi.uima.common.type.BaseToken
   The context of the named entities is a list of tokens - this is what the context analyzer is going to examine.  

So, the work of negating a named entity is done by 
 1) finding negations by the NegationContextAnalyzer 
 2) updating the status of NamedEntities by the NegationContextHitConsumer.  
 
The former is a pretty lightweight wrapper around another class which has all of the negation pattern finding 
logic - org.apache.ctakes.core.fsm.machine.NegationFSM.  If you want to update the pattern matching of negation detection, 
then you would have to do it in that class.  

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updating negex patterns

Updating the negation detection patterns will involve either 1) trial and error experimentation or 2) understanding how
the the NegationFSM works.  The rules, patterns, words that identify negation are hard-coded into the class 
org.apache.ctakes.core.fsm.machine.NegationFSM which is found in the core project.  I would suggest starting off with the 
trial-and-error approach.  For example, if you wanted to add "impossible" to the lexicon of negation words, 
then you could try adding it to the the _negAdjectivesSet and test the behavior.  


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Status Annotator
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The way the status annotator works mirrors very closely how the negation annotator works.  
You are encouraged to read the above section, examine the parameter settings given for desc/StatusAnnotator.xml, 
and look at org.apache.ctakes.core.fsm.machine.StatusIndicatorFSM.