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---+Grammar Engineering Frequently Asked Questions

---++How can I tell if an edge is missing in the parse chart?

If a sentence that you believe should parse isn't parsing, or if it is parsing, but it's not getting the parse you expect, then there are probably edges missing from your parse chart. (If not, see [[RootFail][this FAQ]].)

To find out if this is the case, and to find out which edge is missing, first you must try to parse a sentence, and then [[ShowChart][display the parse chart]].  

Along the left hand side of the parse chart are the word forms from the input sentence.  In the next column are the lexical edges built for each of the words.  In the next column are the edges built from those edges (by the application of lexical rules or or phrase structure rules), etc.

Each edge in the chart is labeled with the portion of the string it spans (e.g., 0-2, meaning the first two words; the numbers label the spaces around the words), a unique edge identifier (in square brackets) and the name of the lexical type or lexical or grammar rule which licensed the edge.

If you click on a word form, all edges which dominate that word form will be highlighted.  If you click on another word form, all edges which dominate both word forms will be highlighted, etc.  This can be useful for determining  which edges (if any) are missing.  You can also click on an edge and select 'Highlight nodes' from the pop-up menu.  This will highlight all descendants and ancestors of that edge.

---+++Related topics
 
   * [[ShowChart][How do I get the LKB to show me the parse chart?]] 
   * [[RootFail][Looking at the parse chart, it seems that I do have an edge that spans the whole chart (accounts for all the words), but the LKB still says no parses found.  What might be going on?]] 

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[[GrammarEngineeringFAQ][Back to FAQs page]]

[[http://courses.washington.edu/ling567/][Back to main course page]]



-- EmilyBender - 02 Nov 2004
Topic revision: r2 - 2005-05-20 - EmilyBender