Integrating NLP Tools in a Distributed Environment: A Case Study Chaining a Tagger with a Dependency Parser

The present paper tackles the issue of PoS tag conversion within the framework of a distributed web service platform for the automatic creation of language resources. PoS tagging is now considered a “solved problem”; yet, because of the differences in the tagsets, interchange of the various PoS taggers available is still hampered. In this paper we describe the implementation of a PoS-tagged-corpus converter, which is needed for chaining together in a workflow the FreeLing PoS tagger for Italian and the DESR dependency parser, given that these two tools have been developed independently. The conversion problems experienced during the implementation, related to the properties of the different tagsets and of tagset conversion in general, are discussed together with the solutions adopted. Finally, the converter is evaluated by assessing the impact of conversion on the performance of the dependency parser by comparing with the outcome of the native pipeline. From this we learn that in most cases parsing errors are due to actual tagging errors, and not to conversion itself. Besides, information on accuracy loss is an important feature in a distributed environment of (NLP) services, where users need to decide which services best suit their needs.