\vspace{-5pt}
\section{Anaphoric Annotation}
\label{sec:background}

\todo{This section is not very useful in its present form - either revise to discuss the specific issues we are interested in, or remove}

We %quickly 
review in this Section the aspects of anaphoric interpretation captured in the {\ARRAU} annotation. 

%\vspace{-5pt}
%\subsection{Identity Anaphora}

%\subsection{Types of Anaphoric Reference}

\paragraph{Identity Anaphora}

Most modern anaphoric annotation projects cover 
%basic 
identity anaphora as in 
\SREF{ex:identity}.

% \begin{equation}
%     \label{ex:identity} \mbox{[Mary]$_i$ bought [a new dress]$_j$ 
%       but [it]$_j$ didn't fit [her]$_i$.}
%       %[Mary]_i bought [a new dress]_j
%       %but [it]_j didn't fit [her]_i.
% \end{equation}
%\vspace{-9pt}
\begin{exe}
\ENEW{ex:identity} [Mary]$_i$ bought [a new dress]$_j$ 
      but [it]$_j$ didn't fit [her]$_i$.
\end{exe}
% \vspace{-9pt}
%
% \ex<ex:identity> [Mary]$_i$ bought [a new dress]$_j$ 
%       but [it]$_j$ didn't fit [her]$_i$.
% \xe
%
% \begin{EXAMPLE}
% \ENEW{ex:identity} [Mary]$_i$ bought [a new dress]$_j$ 
%       but [it]$_j$ didn't fit [her]$_i$.
% \end{EXAMPLE}
However, many other types of identity anaphora exist, as well as other types of anaphoric relations, discussed below.

%\todo{REMOVED SPLIT ANTECEDENT FOR THE MOMENT}
\paragraph{Split-antecedent anaphora} 

In most corpora, plural reference is only marked when the antecedent is mentioned by a single noun phrase. 
But in %However, 
\NEWTERM{split-antecedent anaphors} 
%are also possible 
\CITE{eschenbach1989remarks,kamp&reyle:93}
such as %, as in
\SREF{ex:split}, 
%where 
plural pronoun \LINGEX{they} refers to a set  composed of two  entities introduced by separate  noun phrases.
% Such references are  annotated in, e.g., {\ARRAU} \CITE{uryupina-et-al:NLEJ}, {\GUM} \CITE{Zeldes2017} and  {\PD}  \CITE{poesio-et-al:NAACL19}.

% \vspace{-5pt}
\begin{exe}
\ENEW{ex:split}
    [John]$_1$ met [Mary]$_2$. [He]$_1$ greeted [her]$_2$. [They]$_{1,2}$ went to the movies.
\end{exe}
Such references are not annotated in many corpora,
or 
%In other corpora, 
\LINGEX{They} 
is %would be 
treated as a bridging reference.
% \vspace{-7pt}


% \begin{EXAMPLE}
% \ENEW{ex:split}
%     [John]$_1$ met [Mary]$_2$. [He]$_1$ greeted [her]$_2$. [They]$_{1,2}$ went to the movies.
% \end{EXAMPLE}

\vspace{-5pt}
\paragraph{The semantic function of noun phrases}
% \index{noun phrase}
% \index{noun phrase!semantic function}
% Noun phrases can play different types of \NEWTERM{semantic function}.
The nominal expressions
%anaphoric expressions 
in \SREF{ex:identity} 
%and \SREF{ex:split} 
are examples of 
\NEWTERM{referring} noun phrases, which either introduce new entities in a discourse (first mention of Mary and the new dress)  or link to previously introduced entities (pronouns \LINGEX{it} and \LINGEX{her}).
% The items annotated in anaphoric corpora tend to be a subset of referring {\NP}s.
But 
{\NP}s can serve different functions.
%other types of {\NP}s exist. 
\NEWTERM{Quantificational} {\NP}s %noun phrases
  %\index{noun phrase!quantifier}  
  such as %the  noun phrase 
  \LINGEX{No one} 
  in \LINGEX{No one would put the blame on him/herself} \CITE{partee:72} 
  do not refer to an individual or set of individuals,
  but can still participate in anaphoric relations 
   even though 
   anaphoric reference to quantifiers 
   has distinctive properties 
   %has different properties from anaphoric reference to referring noun phrases 
  \CITE{partee:72} 
   and is subject to semantic constraints %discussed e.g., in 
  \CITE{karttunen:76}.
%   such as 
%   the fact that pronoun \LINGEX{it} in \SREF{ex:karttunen} cannot corefer with the car \CITE{karttunen:76} 
%
% \begin{exe}
% \ex \label{ex:karttunen}
%     [John]$_i$ has [no car]$_j$. *[It]$_j$ is black.
% \end{exe}
\NEWTERM{Predicative} noun phrases 
 %\index{noun phrase!predicative} 
  express properties of
  objects: 
  for instance, in 
  sentence \SREF{ex:non-referring},
  %the clause \LINGEX{John is a good man} 
  %in %example \SREF{ex:anaphora}, 
  the {\NP} %noun phrase 
  \LINGEX{a 
  busy %good 
  place}
  %\LINGEX{a good man} 
  does not introduce a new discourse entity or refer back to an existing discourse entity, 
  but expresses a property. % of John. 
Finally, 
 %\index{noun phrase!expletives} 
in languages like English, 
% CUT TO SHORTEN
% where verbal arguments always have  be explicitly realized, 
forms like \LINGEX{it} and 
\LINGEX{there} can also be used to
express semantically vacuous \NEWTERM{expletives} as well as pronouns,
like the \LINGEX{it} in 
\LINGEX{It is four o'clock}.
%\SREF{ex:non-referring}.
%\LINGEX{It is half past two}. 
Distinguishing referring from non-referring nominals is a part of the task of 
interpreting anaphoric expressions
which cannot  be evaluated 
in corpora where non-referring expressions are not annotated.

\begin{exe}
\ENEW{ex:non-referring} 
      [This] seems to be [a busy place]
\end{exe}

% \vspace{-5pt}
% \paragraph{More complex forms of anaphoric reference}

% The term 'anaphoric reference' covers a wide variety of phenomena, not all of which are annotated in all corpora. 

\paragraph{Discourse deixis} 
The term `anaphoric reference' covers a wide variety of phenomena, not all of which are annotated in all corpora. 
\NEWTERM{Event anaphora} is the type of anaphoric reference
exemplified by \LINGEX{that} in \SREF{ex:dd}, which does not refer to an entity introduced 
by %using 
a nominal, but to the event of a white rabbit with pink ears running past Alice.
% (Both examples from the {\PD} corpus \CITE{poesio-et-al:NAACL19}.)
% as in \SREF{ex:event-anaphora} 
% (where \LINGEX{[that]} arguably refers to the event of a white rabbit with pink ears running past Alice) but not the whole range of 
% abstract anaphora, illustrated by, e.g.,  \SREF{ex:dd}, where again arguably \LINGEX{[this]} refers to the fact that the Rabbit was able to talk. (Both examples from the {\PD} corpus \CITE{poesio-et-al:NAACL19}.)

%\todo{Use a much shorter example!!}

%\todo{Can you say explicitly what the correct antecedent is in the following examples?}
% \vspace{-5pt}
\begin{exe}
% \ENEW{ex:event-anaphora} So she was considering in her own mind (as well as she could, for the hot day made her feel very sleepy and stupid), whether the pleasure of making a daisy-chain would be worth the trouble of getting up and picking the daisies, when suddenly a White Rabbit with pink eyes ran close by her.
% There was nothing so VERY remarkable in \underline{[that]}; nor did Alice think it so VERY much out of the way to hear the Rabbit say to itself, 'Oh dear! Oh dear! I shall be late!' (when she thought it over afterwards, it occurred to her that she ought to have wondered at this, but at the time it all seemed quite natural); ...

\ENEW{ex:dd} ...
when suddenly a White Rabbit with pink eyes ran close by her. 
There was nothing so VERY remarkable in \underline{[that]}; nor did Alice think it so VERY much out of the way to hear the Rabbit say to itself, 'Oh dear! Oh dear! I shall be late!' (when she thought it over afterwards, it occurred to her that she ought to have wondered at \underline{[this]}, but at the time it all seemed quite natural); 
....
% but when the Rabbit actually TOOK A WATCH OUT OF ITS WAISTCOAT-POCKET, and looked at it, and then hurried on, Alice started to her feet, for it flashed across her mind that she had never before seen a rabbit with either a waistcoat-pocket, or a watch to take out of it, and burning with curiosity, she ran across the field after it, and fortunately was just in time to see it pop down a large rabbit-hole under the hedge.

\end{exe} 
% \vspace{-5pt}
Event anaphora is 
a subtype of the more complex phenomenon of \NEWTERM{discourse deixis} \CITE{webber:91,kolhatkar-et-al:CL18} which 
also includes references like  \LINGEX{this} in \SREF{ex:dd}, 
which refers to the fact that the Rabbit was able to talk. 
% A more extensive annotation of event anaphora is found in corpora such as the multi-sentence \ACRO{amr} corpus \cite{ogorman-et-al:COLING18}
% and more complex discourse deictic references are
% %A wider range of discourse deixis is  
% marked in, e.g.,  {\ANCORA} and {\ARRAU}.
Not many corpora attempt to cover the entire range of discourse deixis.

\paragraph{Bridging references and other non-identity anaphora} 

% There are other forms of anaphoric reference besides identity, and there are now a number of corpora annotating (a subset of) these forms. 
Possibly the most studied type of non-identity anaphora is \NEWTERM{bridging reference} or \NEWTERM{associative anaphora}  \CITE{clark:bridging,hawkins:78,prince:81} as in \SREF{ex:bridging}, where bridging reference 
%/ associative anaphora 
\LINGEX{the roof} refers to an object which is related to / associated with, but not identical to, the \LINGEX{hall}.

\begin{exe}
\ENEW{ex:bridging} 
There was not a moment to be lost: away went Alice like the wind, and was just in time to hear it say, as it turned a corner, 'Oh my ears and whiskers, how late it's getting!' She was close behind it when she turned the corner, but the Rabbit was no longer to be seen: she found herself in [a long, low hall, which was lit up by a row of lamps hanging from \underline{[the roof]}].
\end{exe}
Other types of non-identity anaphora also exist, 
besides %which cannot however be  considered 
bridging references.
%because their status is lexically specified.  
Examples include \LINGEX{other} anaphora like \LINGEX{the other} in \SREF{ex:other}, 
as well as \NEWTERM{identity of sense} anaphora such as  \LINGEX{a blue one} in \SREF{ex:sense} \CITE{poesio:ana-book-linguistic}.

\begin{exe}
\ENEW{ex:other}   John gave one book to Mary,  and [the other] to Bill.
\ENEW{ex:sense}   John bought a red ball, and Mary  [a blue one].
\end{exe}

%\todo{It looks like the antecedents are being annotated in these two examples, but please be clear about what they are.}
% \vspace{-5pt}

\paragraph{The interplay between anaphora and other semantic properties of nominals}

Often, whether two mentions corefer depends on how they get semantically interpreted in other respects. 
In \SREF{ex:generic-anaphora}, for instance, whether the mention \LINGEX{bananas} in 40.2 is interpreted as coreferring with mention \LINGEX{bananas} in 37.8 depends on whether these bare plurals are taken to be references to the generic kind \textbf{bananas} \cite{carlson&pelletier:95}.
If those mentions are interpreted as 
non-generic, %referring existentially, 
they would not corefer. 
Some anaphoric corpora therefore include an annotation of noun phrases' genericity \cite{uryupina-et-al:NLEJ,nedoluzhko:LAW13}.

\begin{exe}
\ENEW{ex:generic-anaphora} 
{\small 
\begin{tabular}{lrl}
37.1	& M: & all right\\
37.2	&  : & and then at the same time\\
        &   & ... \\
% 37.3	 : uh what the _heck_ were we doing
% 37.4	 : uh engine ... [tapping]
37.5	& : & E2 was zipping over to Bath \\
        &   & to pick up a boxcar\\
37.6	& : & heading down to Avon\\
37.7	& : & to \\
37.8	& : & collect [bananas]$_i$\\
37.9	& : & and then shipping [em]$_i$ back to \\
        &   & Corning\\
37.10	& : & shortest route \\
        &   & ... \\
% 37.11	 : well
% 37.12	 : it's probably got a _conflict_ with the other guy going
% 	   through Dansville so it's gonna have to go back through Bath 
38.1	& S: & okay so \\
38.2	&: & E2 \\
38.3	& : & goes to Corning\\
38.4	& : & then \\
38.5	& : & on to Bath \\
38.6	& : & and gets a boxcar \\
39.1	& M: & m hm \\
40.1	&S: & then on to Avon \\
40.2	& : & load [bananas]$_{?}$
\end{tabular}}
\end{exe}

\paragraph{Anaphoric reference in dialogue}

%Arguably the most important among these is conversational language in dialogue.
Anaphora resolution in dialogue requires systems to handle 
grammatically incorrect language suffering from disfluencies and
mentions jointly created across utterances \cite{poesio&rieser:completions} or whose function is to establish common ground rather than refer \cite{clark&brennan:90,heeman&hirst:95}.
Dialogue 
contains %involves much 
more deictic reference, vaguer anaphoric and discourse deictic reference,  or speaker grounding of pronouns.
%and long-distance conversation structure. 
These %are 
complexities %that 
are 
normally absent from %often missing in 
news or Wikipedia articles, 
which 
form %constitute 
the bulk of %form a large chunk of 
current datasets for coreference resolution \cite{poesio-et-al:ana-book-corpora}.
There has been some research on coreference in dialogue in English \cite{byron:ACL02,eckert&strube:01,mueller:thesis}, but very limited in scope (primarily %related to 
pronominal interpretation), due to the lack of suitable corpora, although the situation is better for other languages \cite{muzerelle-et-al:LREC14,grobol:2020:thesis}.
