Natural languages are full of collocations, recurrent combinations of words that co-occur more often than expected by chance and that correspond to arbitrary word usages. Recent work in lexicography indicates that collocations are pervasive in English; apparently, they are common in all types of writing, including both technical and nontechnical genres. Several approaches have been proposed to retrieve various types of collocations from the analysis of large samples of textual data. These techniques automatically produce large numbers of collocations along with statistical figures intended to reflect the relevance of the associations. However, noue of these techniques provides functional information along with the collocation. Also, the results produced often contained improper word associations reflecting some spurious aspect of the training corpus that did not stand for true collocations. In this paper, we describe a set of techniques based on statistical methods for retrieving and identifying collocations from large textual corpora. These techniques produce a wide range of collocations and are based on some original filtering methods that allow the production of richer and higher-precision output. These techniques have been implemented and resulted in a lexicographic tool, Xtract. The techniques are described and some results are presented on a 10 million-word corpus of stock market news reports. A lexicographic evaluation of Xtract as a collocation retrieval tool has been made, and the estimated precision of Xtract is 80%.

. This paper presents a lexical choice component for complex noun phrases. We first explain why lexical choice for NPs deserves special attention within the standard pipeline architecture for a generator. The task of the lexical chooser for NPs is more complex than for clauses because the syntax of NPs is less understood than for clauses, and therefore, syntactic realization components, while they accept a predicate-argument structure as input for clauses, require a purely syntactic tree as input for NPs. The task of mapping conceptual relations to different syntactic modifiers is therefore left to the lexical chooser for NPs. The paper focuses on the syntagmatic aspect of lexical choice, identifying a process called "NP planning". It focuses on a set of communicative goals that NPs can satisfy and specifies an interface between the different components of the generator and the lexical chooser. The technique presented for NP planning encapsulates a rich lexical knowledge and allows ...

For collaborative learning environments, the support of interaction is mainly focused on communication since directly experiencing a situation and learning by observing are mostly inapplicable. We describe communication based on a context-oriented communication model that focuses on the dialogical communication and mediation of context. The model leads to an abstract identification of general communication tasks and the use of learning material in collaborative learning processes. The difference between uploading material and communicative contributions has to be made distinct and different ways of combining both need to be supported. The prototype system "KOLUMBUS" which has been used for an experimental investigation in a university course and in a working group is used to demonstrate such features. The evaluation brought evidence that the concept of annotations to support context-oriented communication in collaborative learning processes is well received.