  The increasing availability of corpora annotated for linguistic structure
prompts the question: if we have the same texts, annotated for phrase structure
under two different schemes, to what extent do the annotations agree on
structuring within the text? We suggest the term tree alignment to indicate the
situation where two markup schemes choose to bracket off the same text
elements. We propose a general method for determining agreement between two
analyses. We then describe an efficient implementation, which is also modular
in that the core of the implementation can be reused regardless of the format
of markup used in the corpora. The output of the implementation on the Susanne
and Penn treebank corpora is discussed.
