User Tools

Site Tools


gum:rst

Rhetorical Structure Theory Annotation

Text segmentation

The main sentences (or equivalent fragments/utterances) identified as <s> tags in the markup phase, which are also the basis of syntactic analysis in the dependency annotation phase, are always separate segments for the purpose of RST analysis.

Additional segments may be needed, often to delineate subordinate clauses that match an RST relation function. In practice, the following types of clauses are usually made into separate segments:

  • Conditional clauses (with 'if' or other complementizers) are typically separated and later placed in the 'conditional' relation with the segment containing the clause they modify.
  • Circumstance clauses, especially denoting time and place (e.g. temporal 'while' clauses), are similarly segmented apart.
  • Infinitive clauses of purpose ('in order to', or just 'to' infinitive with the same meaning:
    • [We went to Turkey] [to enjoy some sunny weather]
  • Note that purpose clauses are attached to verbs. Do not segment infinitives modifying a noun, e.g.:
    • NOT CORRECT!! [we had a chance] [to succeed] (“to succeed” is also not the purpose of “we had a chance”)

Coordinate clauses

Most full clauses coordinated by 'and', 'or' or 'but' are made into independent EDUs. The coordinating conjunction belongs to the second EDU, e.g.:

  • [call the local harbor master] [and he will sort you out]

Exceptions to splitting EDUs include:

  • Coordination is inside a subordinate/relative clause, which is not eligible to be an EDU:
    • [They told me to call the harbor master and he will sort me out]
  • When the subject is shared across both clauses (i.e. VP coordination) and no EDU intervenes, the sentence is considered a single EDU:
    • [The harbor master called and sorted us out] (harbor master is subject of both verbs and not repeated)
  • Exception: when an adverbial clause intervenes between two parts of a VP coordination, we make multiple EDUs. This also applies if we have multiple coordinate VPs:
    • [Łódź was created during the 19th century textile boom]sequence [to house industry workers]purpose [and rapidly grew…]sequence
    • [Łódź was created during the 19th century textile boom]sequence [and was built up]sequence [to house industry workers]purpose [and then rapidly grew…]sequence

Subject and object clauses

Subject and object clauses are not segmented:

  • [John said that Mary would come]
  • [That he said so angered Bill]

The rhetorical act is considered to be reporting the fact that something was said; the nested rhetorical structure of what was said in itself is not analyzed further if the sentence embeds it below a verb of saying.

Relations and Conventions

Relations in minimal set

  • Presentational
    • Antithesis
    • Background
    • Concession
    • Evidence
    • Justify
    • Motivation
    • Preparation
  • Subject matter
    • Cause
    • Circumstance
    • Elaboration
    • Evaluation
    • Purpose
    • Result
    • Solutionhood
    • Restatement
    • Multinuclear relations
      • Contrast
      • Sequence
      • Restatement
      • Joint

Complete trees

  • Each document should form a complete 'tree' in the sense that there are no separate groups of segments or 'islands' that are not linked by relations.
  • If several different topics are discussed which form encapsulated 'islands' with no relations between them, then by convention these will all be joined at the end of the annotation process using a multinuclear group dominating the islands with the joint relation.
  • Some typical scenarios of how 'islands' are formed and grouped include:
    • The series of questions & answers (QAs) in an interview. If no specific rhetorical progression is found between multiple QAs, then each pair may form its own island and these are connected by a joint. Items outside the QA sequence may join the tree at a higher level (e.g. headings as preparation for the entire interview, or an introductory paragraphs giving background about the speakers).
      • Note that although the questions in an interview appear in sequence, they are not labeled as a sequence, unless the answers themselves form a chronological succession (answer 1: “first I did X”, answer 2: “later we decided to do Y”). Generally the collection of answers simply forms a joint. The figure below gives an example of this structure.

  • The subsections of a travel guide can form islands that should be joined by a joint. Typically sections like ‘getting there’ and ‘understand’ are autonomous and are analyzed internally, then joined at the top with the rest of the article, though the main heading may precede the entire joint and modify it (see below).
  • In how-to guides, the subsections (preparations, tips, warnings), or different methods (method 1, method 2…) are often separate and can be analyzed internally, then connected by a joint or sequence unifying all steps in a method, and a higher joint unifying the methods.

Avoiding chains

A satellite which has a satellite almost always has a span grouping the lower satellite before it modifies something else. In the example below, if we think that 32 is an elaboration of 31, and 31 is an elaboration of 30, then by extension, 32 is also part of the complex elaboration of 30. This means that 31+32 need to be grouped together first under a span, and then form the higher elaboration. The bad example on the right is a case of what we call 'chaining' (a flat sequence of arrows).

Handling questions

  • Questions are typically seen as satellites to their respective answers and are linked using the ‘solutionhood’ relation.
  • When connecting individual sections or QA pairs to the main joint of an article, a span should be used above the entire QA/section subtree to make it clear that the entire subtree is a member of the joint. Do not link just the main segment to the joint directly if there are other segments in the subtree.

Building a hierarchy

  • Ideally a satellite and nucleus should form a group covered by a span, and one nucleus should not have more than one incoming satellite. For example, if a satellite provides background to a nucleus which also has an elaboration, it may make more sense to see the background as modifying the entire span of nucleus and elaboration (since background is given for the benefit of both other EDUs).

  • In cases of two equal satellites to the same nucleus with the same function, a joint multinuc can be used. This is the preferred structure if both satellites are seen to provide a similar or closely related contribution. For example, the structure on the left is preferred to the structure on the right below, because both satellites give the same elaborating information, namely specifying the members of an organization. If the satellites have different functions or give rather different details, then they can be attached directly to the nucleus without forming a joint first.

Avoiding empty hierarchy

You should not have spans that have no incoming connections except for another span or multinuc above them. Spans are there to group elements, so that they can have an incoming or outgoing connection relating to some other node. In particular, EDUs should not have a span containing only themselves:

Headings, dates, images and captions

  • Headings are typically seen as a ‘preparation’ for the following group of segments comprising the section under the heading. This is especially true if the heading does not contain information not covered again in the section. The ‘preparation’ should target an added span covering the entire section, and not just the head segment of the section. (see image below)
  • In some cases, the heading contains the main gist of a (usually short) section, and the section itself may be seen as an elaboration of the heading.
  • Images themselves do not form RST segments, however when their captions are part of the text, the entire effect of the image and caption may be taken into consideration. Most often (or when in doubt), an image and its heading will provide ‘background’ for the subsequent text, but under some circumstances a caption and the related image may provide ‘evidence’ or serve as an ‘elaboration’, or in rare cases even other relations.
  • If there is a heading ‘preparation’ followed by a ‘background’ image and caption at the beginning of a section, typically the caption (standing in for the image as well) is seen as giving background to the entire section, and the heading is a preparation for the group of segments containing both the section and the background caption.
  • If there is a secondary caption or a caption-internal segment giving attribution, such as the photographer’s name or the name of a person quoted in a block quote, these may be seen as an ‘elaboration’ or the primary caption segment.

(e.g. [image of a magician] ←elaboration– [photo: Paul Budd])

  • If there is a segment detailing the date (e.g. for a news item or interview), and the date applies to the entire text, it may be seen as a ‘circumstance’ to the entire text. If the date is qualifying a more specific sub-part of the document it may be attached accordingly, again using the ‘circumstance’ relation.
  • If a main heading is reiterated in the text, this is not generally seen as a ‘restatement’, but rather the heading is seen as ‘preparation’ for the section in the interest of consistency.

Choosing between relations

Insertion tests

When considering two similar relations between sentences without an explicit connective like 'beacuse' or 'if', sometimes inserting a connective or phrase can help to disambiguate. Useful phrases include:

  • 'because' - if you can insert 'because' between clauses, often you have a cause or result relationship
  • 'the reason I say this…' - if you can insert this, it can indicate justify
  • 'what you need to know about this…' - can indicate background

Some examples:

  • “ [ IE's market share has dropped to 56%.] [Mozilla's Firefox has been actively increasing its market share] ” - in this example, it's easy to insert 'because', and the relationship is cause.
    • If this were justify, we could say “the reason I say this is that Mozilla… ”
    • If it were background, we could say “what you need to know about this is that Mozilla…” which is also more forced
  • “ [York is a fairly small city -] [four days is enough to see the major sights] ” - in this example, we can add “the reason I say this is…” between the two units, and the relation is justify
    • If it were cause we could say “the city is small because four days is enough…” - but actually it is not small because of this fact
    • It if were background, it would be as natural or more natural to say “York is small. What you need to know about this is that four days are enough…”
gum/rst.txt · Last modified: 2017/04/19 09:57 by amir