What is Two-Level Morphology?

Question

In Natural Language Processing what are the two levels of this two-level Morphology framework ?

Answer 1

There are lexical and surface levels in this framework, hence the name two-level morphology. The surface level is the actual realization of words as they appear in the final form. The lexical (a.k.a dictionary) level corresponds to the combination of roots and affixes that are chained together with boundary markers. For instance, for the present tense third person singular form of the verb "try":

lexical level: try+s
surface level: tries

In this framework, these two levels are connected through a series of finite state transducers and form a single combined automaton.

For more information consult this document.

UPDATE: Also have a look at the documentation for twol, a Python package developed within this linguistic framework. For a detailed theoretical treatment, you can have a look at Koskenniemi's original work here.