Ambiguity resolution

There are two primary types of ambiguity that an Apertium pipeline can deal with:

• Morphological ambiguity — when a single form has multiple analyses. The solution to this is #Morphological disambiguation.
• Lexical ambiguity — when a single lexical item (lemma+POS+subcategory) has multiple translations. The solution to this is #Lexical selection.

Distinguishing between the two

Morphological ambiguity

Imagine you have a word that has two different tagsets, e.g.

^houses/house<n><pl>/house<v><tv><p3><sg>$
^this/this<det><dem><sg>/this<prn><dem><sg>$

Normally your analyser will randomly output ("choose") one of these. Now imagine you have a sentence where the wrong analysis is "chosen" (in this case, twice!):

^The/The<det><def>$ ^motel/motel<n><sg>$ ^houses/house<n><pl>$ ^this/this<prn><dem><sg>$ ^dog/dog<n><sg>$^./.<sent>$

In both of these examples, there is a different lemma+POS+subcategory. However, the following is also an example of morphological ambiguity:

^deer/deer<n><sg>/deer<n><pl>$

As with the previous examples, both analyses are correct output from the transducer, but which one is correct in a given context will vary. (The assumption is that one and only one analysis will be correct for a given context.)

The goal of morphological disambiguation is to choose the correct analysis in cases like these based on the surrounding words.