Get GrammaticalRelation of root node - parsing

Question

I'm attempting to parse Medical research reports, using the Stanford NLP. I can get the GrammaticalRelation of all the nodes except the first or root node. How do I get this valus.
I have written a java program which parses reports by getting the dependency graph and can get the child pairs of all the nodes except the root node.
public void DocAnnotationParse(String Input_text) {
Annotation document = new Annotation(Input_text);
Properties props = new Properties();
//props.setProperty("annotators", "tokenize,ssplit,pos,lemma,ner,parse");
props.setProperty("annotators", "tokenize,ssplit,pos,parse");
StanfordCoreNLP pipeline = new StanfordCoreNLP(props);
pipeline.annotate(document);
int sentNum = 0;
Map<String, Map<String, Map<String,IndexedWord>>> sentMap = new LinkedHashMap<>(); // A map contains maps of each sentence
for (CoreMap sentence : document.get(CoreAnnotations.SentencesAnnotation.class)) {
SemanticGraph dependencyParse = sentence.get(SemanticGraphCoreAnnotations.BasicDependenciesAnnotation.class);
IndexedWord firstVertex = dependencyParse.getFirstRoot();
Map<String, Map<String,IndexedWord>> outterMap = new LinkedHashMap<>();
RecursiveChild(outterMap, dependencyParse, firstVertex, 0);
sentMap.put(Integer.toString(++sentNum), outterMap);
logger.debug("outtermap: "+outterMap);
}
logger.debug("all sentMaps: "+sentMap);
PrettyPrintBySentence(sentMap);
}
public void RecursiveChild(Map<String, Map<String, IndexedWord>> outterMap,
SemanticGraph dependencyParse,
IndexedWord vertex, int hierLevel) {
Map<String, IndexedWord> pairMap = new LinkedHashMap<>();
pairMap.put("Root", vertex);
List<IndexedWord>indxwdsL = dependencyParse.getChildList(vertex);
List<Pair<GrammaticalRelation,IndexedWord>>childPairs = dependencyParse.childPairs(vertex);
List<IndexedWord> nxtLevalAL = new ArrayList<>();
if(!indxwdsL.isEmpty()) {
++hierLevel;
for(Pair<GrammaticalRelation, IndexedWord> aPair : childPairs) { //at level hierLevel x
logger.debug(aPair);
String grammRel = aPair.first.toString(); //Gramatic Relation
IndexedWord indxwd = aPair.second;
pairMap.put(grammRel, indxwd);
List<Pair<GrammaticalRelation,IndexedWord>>childPairs2 = dependencyParse.childPairs(indxwd);
if(!childPairs2.isEmpty()) {
nxtLevalAL.add(indxwd);
}
}
}
String level = Integer.toString(hierLevel);
outterMap.put(level, pairMap);
//Go to each lower level
for(IndexedWord nxtIwd : nxtLevalAL) {
RecursiveChild(outterMap, dependencyParse, nxtIwd, hierLevel);
}
}
The childPair for the root vertex does not contain a Grammatical Relation, which I want. Looking at the dependency graph there is no value but just the string root. How do I get the Grammatical Relation for that node. For example the simple sentence "I love French fries." gives the graph:
-> love/VBP (root)
-> I/PRP (nsubj)
-> fries/NNS (dobj)
-> French/JJ (amod)
-> ./. (punct)

Answer 1

Hi I'm not a linguistics person, but my understanding is that there is simply a ROOT node outside of the SemanticGraph, and a root edge points from the root to a word(s) in the sentence.
So in your example the ROOT node is attached to the word love with the root relation.
If you look at the code of SemanticGraph it explicitly states:
* The root is not at present represented as a vertex in the graph.
* At present you need to get a root/roots
* from the separate roots variable and to know about it.
You can access the list of roots (I guess there can hypothetically be more than one?) with the getRoots() method. But I think all that means is that a root edge flows from the ROOT node into those words.
If you want an actual Java object to represent that rather than a String, there is edu.stanford.nlp.trees.GrammaticalRelation.ROOT which represents this relationship between the "faked ROOT node" and the roots.
/**
* The "root" grammatical relation between a faked "ROOT" node, and the root of the sentence.
*/
public static final GrammaticalRelation ROOT =
new GrammaticalRelation(Language.Any, "root", "root", null);