Enrichring the Ita-TimeBank with Narrative Containers
Authors: Alice Bracchi, Tommaso Caselli, Irina Prodanof (Università di Pavia, VU Amsterdam, 2016)
Topic: Lexical and Semantic Resources and Analysis

Abstract
This paper reports on an annotation experiment to enrich an existing temporally annotated corpus of Italian news articles with Narrative Containers, annotation devices representing temporal windows in text and marking up very informative temporal relations between temporal entities. The annotation has shown that the distribution of Narrative Containers is sensitive to the text genre and may be used to facilitate the creation of informative timelines.

Introduction
Research in Temporal Processing has seen an increasing interest thanks to the availability of annotation schemes and corpora in multiple languages AUTHOR, and the organization of evaluation campaigns (TempEval AUTHOR, Clinical TempEval AUTHOR, Cross-Document TimeLine AUTHOR, Temporal QA AUTHOR), and EVENTI AUTHOR). This has established best practices, common evaluation frameworks, international standards (e.g. ISO-TimeML AUTHOR), and approaches to solve such a complex task. However, the expression of time in text/discourse is by no means obvious and the automatic extraction of timelines is not a solved task yet. One of the limits of current annotation frameworks and corpora relies mainly in the sparseness of the available temporal relations and in the fine-grained values used to classify the temporal links. For instance, in the TempEval-3 corpus the ratio between temporal relations and event plus temporal expressions is 0.8 AUTHOR for 13 temporal values. In the EVENTI corpus, the ratio is even smaller, only 0.19 for 13 temporal values.~.} Furthermore, in some cases annotation guidelines are not informative enough concerning what types of temporal links to annotate, or they force the annotation of temporal relations between pairs of events when they should not be annotated. Attempts to overcome these limits have focused on three main strategies: i.) annotating particular sets of temporal relations AUTHOR; ii.) elaborating detailed annotation guidelines for each kind of temporal relations (event-temporal expression pairs, event-event pairs, and temporal expression-temporal expressions pairs); and iii.) developing densely connected temporal graphs, where all valid relations among the temporal entities (events and temporal expressions) are marked up, including inferred relations based on transitive properties of the temporal relations (e.g. if event A is BEFORE event B and event B IS\_INCLUDED in event C, then event A is BEFORE event C) AUTHOR. We consider these solution as partial as they are not able to address the issue of identifying and extracting informative timelines, i.e. a set of maximally informative temporal links where relevant events in a text/discourse are correctly anchored to time, and then chronologically ordered. This paper reports on the first annotation effort to enrich existing resources for Temporal Processing in Italian by adopting a document-level approach rather than a sentence-level one. Following the proposal of Narrative Containers (NCs) AUTHOR, as embedding intervals where events occur, we developed an annotation scheme for their identification on the EVENTI corpus AUTHOR~}, as a strategy to increase the informativeness of the existing annotations and, possibly, improve systems's temporal awareness. The remainder of this paper is structured as follows: the EVENTI corpus will be shortly introduced in Section~sec:eventi, with a particular emphasis on the available temporal relations. Section~sec:nc will present the notion of Narrative Container and the proposed annotation scheme. In Section~sec:itatbNc the results of a pilot annotation on the EVENTI dataset will be reported. Finally, conclusion, future work, and a pointer to the annotated data and guidelines will be reported in Section~sec:conclusion.

Conclusion
This paper reports on a first proposal of an annotation scheme and accompanying annotated data for NCs in Italian news articles. The NC annotation is an additional layer on top of already available data for Temporal Processing in Italian. It addresses pending issues (e.g. the annotation of the temporal relations between event and the Document Creation Time) and increases the informativeness of the document timelines. Overall, we observed that there is a preference for NC to be realized by timexes in a limited time span. However, NCs may also be realised by events. In this case, nouns and verbs have a similar distribution with a preference for events which have a central role in the news or facilitate the clustering of the information (e.g. reporting events). Such a behaviour is different with respect to clinical narratives where nominal events are more frequently selected as NC AUTHOR. This suggests that different text genres present different ways of organizing events on a timeline. The introduction of the factuality parameter to select the anchoring events is a strategy to clean timelines and to move Temporal Processing from a single document to a cross-document task. Future work will aim at assessing the reliability of the proposed scheme via an inter-annotator agreement study and at completing the annotation of the entire EVENTI corpus. Finally, the annotated data and guidelines are publicly available~} to encourage additional testing and experiments.