Treebanks as a learners’ corpus

Morphologically annotated corpora are usually seen – at least in Greek and Latin philology – as scholarly resources. But they can be used to teach and learn Greek and Latin as well. We can use parts of annotated sentences as material for exercises.

We want to start simple, very simple: let’s offer our learners some prepositional phrases and some predicate - object (V - O) sentence fragments. The initial step is to find such phrases in the treebank and retrieve them.

My experiment has been done with the PROIEL treebank, for two reasons. First, it is one of the two Greek and Latin treebanks available under a CC license. Second, it contains New Testament in Greek and Latin. Regardless of the religious and moralistic part of the experience, I have to agree with Dwane Thomas – the Vulgate is a great place to find real, but stylistically simple Latin; “start with the easy books before you jump into the hard ones” is always a great advice.

By annotating the books of the New Testament, PROIEL has annotated a lot of simple Greek and Latin phrases. And how do we retrieve them? In my case, by writing several XQuery functions. Two, basically identical, XQuery scripts are in the Discipulus working repository on Bitbucket – one to find prepositional phrases and one to find verbs with objects. Here I’ll comment on more interesting parts of the scripts.

The structure of PROIEL XML files makes it possible to limit searches to specific books and chapters of the New Testament. We retrieve prepositions using an XPath like this:

db:open("proiel-biblia-tb","latin-nt.xml")/proiel/source/div[@alignment-id="41"]/div[@alignment-id="7"]/sentence/token[@part-of-speech="R-"]

Retrieving of words dependent on the preposition is then done by a recursive function down_tree:

declare function local:down_tree($root){
  let $id := $root/@id
  let $down_t := $root/../*:token[@head-id=$id]
  (: check if there is a dependent word :)
  return if ($down_t[@head-id]) 
  (: if there is one, the function should recursively call itself :)
  (: to retrieve other dependent words :)
         then ( $down_t/@form/string() , local:down_tree($down_t) )
  else $down_t/@form/string()
};

Running the script against the Latin part of our proiel-biblia-tb database, we learn something about the limitations of annotated treebanks:

<phr citation-part="MARK 7.21">
  <w>ab</w>
  <w>intus</w>
  <w>de</w>
  <w>corde</w>
  <w>hominum</w>
</phr>
<phr citation-part="MARK 7.1">
  <w>ad</w>
  <w>eum</w>
</phr>
<phr citation-part="MARK 7.31">
  <w>ad</w>
  <w>mare</w>
  <w>Galilaeae</w>
</phr>

<phr citation-part="MARK 7.24">
  <w>in</w>
  <w>fines</w>
  <w>et</w>
  <w>Tyri</w>
  <w>Sidonis</w>
</phr>

<phr citation-part="MARK 7.19">
  <w>in</w>
  <w>non</w>
  <w>cor</w>
  <w>eius</w>
</phr>

<phr citation-part="MARK 7.13">
  <w>per</w>
  <w>traditionem</w>
  <w>vestram</w>
  <w>tradidistis</w>
  <w>quam</w>
</phr>

While the results such as the first three are immediately useful (“ab intus de corde hominum”), the last three should be modified before we can integrate them in an exercise. “In non cor eius”? The word order is not right! Here I can only agree with James Tauber’s insight – treebanks are not a tool for everything we want to do with language. There are linguistic features treebanks cannot capture. For example, the features connected with word order: informational structure and stylistic effects.

Now, however, we have a brief and relatively simple XQuery that pulls out (mostly) meaningful prepositional phrase-fragments from a dependency treebank. And the same script should work for Greek and Old Church Slavonic, but more about that experiment later.

Treebanks for learners

Finding simple phrases with XQuery and dependency trees

Treebanks as a learners’ corpus