Towards visualizing linguistic patterns of deliberation: a case study of the S21 arbitration

1. Introduction
This paper reports on the interdisciplinary project VisArgue which is concerned with the automatic linguistic and visual analysis of political discourse with a particular focus on the concept of deliberative communication 12345. According to the theory of deliberative argumentation, stakeholders participating in a multilog, i.e. a multi-party conversation, should justify their positions truthfully and rationally and should eventually defer to the better argument.

Automatically measuring the deliberative quality of a multilog calls for an identification of linguistic cues that shed light on issues such as objective vs. subjective argumentation, invocation of the common good or democratic notions as part of the argument. Notions such as speaker stance, speaker belief/certainty are also immediately relevant, as is an analysis of rhetorical devices known to trigger conventional implicaturs 6. In short, a promising way of arriving at an operationalization of the indications for the deliberative quality of a multilog is a linguistic analysis of the linguistic cues present in the multilog.

This paper presents on-going work on analyzing strategies for argumentation via automatic means, using public data from a German arbitration. In addition to a thorough linguistic analysis of the relevant parameters, we provide a computational implementation that automatically annotates the corpus with respect to pragmatically relevant features. This implementation combines a rule-based system that reflects deep linguistic analysis with a visual analysis system that also provides results with respect to more shallow natural language processing methods such as keyword identification, topic modeling, and standard calculations with respect to length of utterances, amount and type of turn-taking, etc.

2. Data
In Germany, the method of deliberative discourse has been increasingly applied to the resolution of large-scale public conflicts since the early 1990s. One recent well-known example is the public arbitration process on "Stuttgart 21" (S21), a new railway and urban development project in the city of Stuttgart. In response to massive public criticism of the project, a public arbitration procedure was established. The data for our initial investigation are the transcribed minutes of the S21 arbitration process, which consist of nine days of sessions, each lasting for around seven hours, with a total of about 70 different speakers. The transcripts consist of spoken German conversation between mediator, experts, project supporters and opponents and are converted into an XML-readable format in order to facilitate later processing and annotation. Based on the information contained in the web transcripts, the XML trancripts are annotated with speaker information and the general topic of the session. Overall, the transcripts contain around 265.000 tokens in 1330 utterances.

In order to arrive at a more fine-grained analysis of the discourse, all utterances have to be split up into elementary discourse units (EDUs) 7. Although there is no consensus in the literature on what EDUs are, in general, each DU is assumed to describe a single event (e.g., 8). In the case at hand, we approximate this by treating all lexical items between two punctuation marks as belonging to one DU, a method that is commonly assumed in discourse parsing.

3. Linguistic background
A central aspect of our work is a linguistically motivated operationalization of features that indicate the deliberative quality of a multilog, important parameters being the realization and the communicative function of arguments in the discourse as well as speaker stance and speaker belief. We have decided to initially focus on just two of the relevant linguistic parameters found in German: the interaction between causal discourse connectors and modal particles.

Causal discourse connectors (e.g., da, weil, denn, zumal 'because (of)/due to/as') generally introduce a justification of a speaker's statement (e.g., 9). These connectives and the justification they indicate can be extracted automatically. However, the precise shade and force of the argument being made, including speaker stance and speaker belief are modulated in spoken German by a heavy use of modal particles (e.g., 1011). For instance halt or eben indicate a conventional implicature that the speaker believes the argument to refer to an immutable constraint imposed by the outside world, exemplified in (1). The particle ja in (2), in contrast, signals that the speaker assumes that the content of the argument is part of the common ground of the multilog participants.

(1) [...] weil halt in dem Bereich die meisten Autos unterwegs sind.

[...] as HALT in Art area Art most car.Pl underway be.3.Pl

'[...] because most cars are underway in this area.' (Dr. Heiner Geissler, S21, Nov. 4th 2010)

(2) [...] da Sie ja gesagt haben, dass [...]

[...] as Pron.2.Sg.Pol JA say.Past.Part have.Inf that [...]

'[...] as you JA said that [...]' (Tanja Gönner, S21, Nov. 4th 2010)

3.1. Ambiguity
Ambiguity presents a serious problem for the automatic extraction and identification of both causal connectors and modal particles. For example, especially da 'as' presents a challenge for automatic processing, because of its multi-functional usage as either the temporal or locative pronoun 'there' or as a connector meaning 'because'. However, such ambiguities can be largely resolved by taking linguistic factors such as the position of the connector, its neighboring elements and the general structure of the carrier sentence into account. In (3), we schematize the identification rule for the German causal connector da 'as'.

(3) IF da not followed by verb AND

da not preceded by a particle or another causal connector AND

final verb is an infinitive THEN

da is a causal connector.

The same procedure is followed with respect to modal particles such as eben, which can be a focus particle, a temporal adverbial meaning 'just', or a modal particle that indicates the speaker's resigned acceptance of a fact due to an immutable constraint 12.

3.2. Inference rules
While these two dimensions are by themselves important for the interpretation of a given discourse, the additional benefit for measuring deliberation results from a combination of the two dimensions. Taking the example in (1), the inference rule in (4) yields the annotation in Figure 1.

(4) IF causal connector found AND causal connector followed by particle denoting immutable constraint THEN annotate the DU start tag with <DiscRel="justification" CI="immutable_constraint">

Fig. 1: Annotation of example (1).

On the other hand, the rule in (5) deals with the combination of the causal connector da and the modal particle ja, rendering the annotatation of example (2) in Figure 2. (5) IF da is used as causal connector AND da is followed by particle denoting common ground THEN annotate the DU start tag with <DiscRel="justification" CI="common_ground">.

Fig. 2: Annotation of example (2).

These inferences, which perform context-sensitive linguistic annotation of discourse units, help to interpret the whole discourse and shed light on the way speakers and listeners interact, incorporating detailed linguistic knowledge about syntax and discourse pragmatics.

Despite the comparatively small corpus, it is nevertheless difficult to see overall patterns of argumentativity at a glance, while still maintaining a detailed view on single annotations. In order to overcome this drawback, we introduce a visualization system which encodes those annotations visually and makes the patterns more accessible.

4. Visualizing argumentativity
The visualization of linguistic patterns has been shown to shed light on a number of phenomena, from theoretically motivated topics like phonological patterns 13 and lexical semantic change 1415 to machine learning issues with respect to clustering 16. The goal of visualizing the structure of argumentativity across the discourse is twofold: First, patterns of argumentation that have been identified through the linguistic inference rules can be analyzed in their context. Second, the distribution of arguments over the course of the conversation may reveal additional knowledge on the deliberative quality of different parts of the overall discourse.

Figure 3 shows a visualization of parts of the S21 arbitration session on Nov. 4th 2010, each sentence occupying one line, each speaker turn contained in a grey square. The bars marked in yellow represent discourse units containing justifying statements. The tool is interactive in that the user can zoom in and out of the discourse and can investigate the relevant discourse units in detail without loosing the overall distribution. A detailed view on the data is shown in Figure 4.

Fig. 3: Visualization of justifying statements in the S21 arbitration on November 4th, 2010.

Fig. 4: Detailed visualization of justificational discourse units.

5. Summary and future work
This paper presents an approach of operationalizing the notion of deliberation using discourse connectors and modal particles in order to shed light on the way arguments are exchanged and how speakers and listeners relate to them. By using a visualization approach, the annotated data can be inspected over the whole discourse, allowing for an interpretation of the role that argumentativity plays in the arbitration. In the future, we will incorporate more linguistic cues that are relevant for deliberative communication and also deal with multiword instances that are relevant on a number of levels. With the increasing number of annotation levels, the visualization will be extended to show the interactions between different levels, allowing for more insights into discourse structure and eventually deliberation.

Acknowledgements
We thank Mennatallah el Assady, Manuel Hotz and Rita Sevastjanova for their help with implementing the discourse visualization and the German Ministry for Education and Research (BMBF) for their funding under the eHumanities research grant 01UG1246.

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