\section{The Universal Anaphora Initiative}
\label{sec:UA}

%\subsection{Universal Anaphora} 

The \NEWTERM{Universal Anaphora} ({\UA}) initiative
% \footnote{\url{https://universalanaphora.github.io/UniversalAnaphora/}}  
was launched in 2020
in order to  enable further progress in the empirical study of anaphora by coordinating the many existing efforts to annotate not just identity coreference, but all aspects of anaphoric interpretation from identity of sense anaphora to bridging to discourse deixis; and not just for English, but all languages.
Progress so far includes a first proposal concerning the range of phenomena to be covered, as well as a survey of the range of existing anaphoric annotations and a proposal for a markup format extending the {\CONLL}-U format developed by the \NEWTERM{Universal Dependencies} initiative
% \footnote{\url{https://universaldependencies.org/}} 
with mechanisms for marking up the range of anaphoric information covered by {\UA}.
% Crucially, a scorer able to evaluate all types of anaphoric reference in the scope of the proposal was also developed, which we used in this shared task.
% The scorer is briefly discussed in Section \ref{sec:task:scorer}.

\subsection{Scope: Beyond 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 that are not annotated in {\ONTONOTES} but are annotated in other  corpora. 
%In this Section we list them.

%MENTION UA HERE?

\paragraph{Split-antecedent anaphora} 

In {\ONTONOTES}, plural reference is only marked when the antecedent is mentioned by a single noun phrase. 
However, \NEWTERM{split-antecedent anaphors} are also possible \CITE{eschenbach1989remarks,kamp&reyle:93}, as in \SREF{ex:split}.  
These are also cases of  plural identity coreference, 
but to sets composed of two or more 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}
% \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}

\paragraph{Discourse deixis} 

In {\ONTONOTES}, \NEWTERM{event anaphora}, a subtype of \NEWTERM{discourse deixis} \CITE{webber:91,kolhatkar-et-al:CL18} is marked, 
as exemplified by \LINGEX{that} in \SREF{ex:dd}, which 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.,   \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}.
% (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}

\paragraph{Bridging references} 

% 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 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}.
In {\UA}, 
non-identity anaphora is also taken 
%We also take bridging reference 
to cover  \LINGEX{other} anaphora 
%as in \LINGEX{the other} in \SREF{ex:bridging},
%\SREF{ex:other}, 
as well as other cases of association such as identity of sense anaphora, etc. \CITE{poesio:ana-book-linguistic}.

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

% There were doors all round the hall, but they were all locked; and when Alice had been all the way down one side and up \underline{[the other]}, trying every door, she walked sadly down [the middle], wondering how she was ever to get out again.

% \ENEW{ex:other} 
% 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 the roof.

% There were doors all round the hall, but they were all locked; and when Alice had been all the way down [one side] and up \underline{[the other]}, trying every door, she walked sadly down the middle, wondering how she was ever to get out again.

\end{exe}
% \vspace{-5pt}

\subsection{CONLL-UA}

The markup format proposed in {\UA}, called {\CONLLUA},\footnote{\url{https://github.com/UniversalAnaphora/UniversalAnaphora/blob/main/documents/UA_CONLL_U_Plus_proposal_v1.0.md}} is an extension of the {\CONLLU} tabular format defined for Universal Dependencies.
The format specifies %requires 
the following layers in addition to those defined in {\UD}:
% \vspace{-7pt}
\begin{itemize}
    \item an \CODE{Identity} layer, specifying the entity a markable refers to  in the case of a referring markable and, optionally, whether the markable is referring or not,  what its head is, 
    and, for split antecedents, the set they belong to;
    % \item a \CODE{Split} layer, specifying for each split antecedents the set they belong to;
    % \vspace{-7pt}
    \item a \CODE{Bridging} layer, specifying the anchor, its most recent mention, and, optionally, the associative relation;
    % \vspace{-7pt}
    \item a \CODE{Discourse\_Deixis} layer, whose markables specify the non-nominal antecedents of discourse deixis, represented exactly as in the \CODE{Identity} layer.
    This makes it possible to adopt for discourse deixis the same metrics used for identity anaphora.
\end{itemize}
% \vspace{-7pt}
Two inter-convertible versions of the {\UA} format have been defined: the `compact' and the `exploded' formats. 
The `compact' format encodes all the anaphoric interpretations in the `\CODE{Misc}' column of the {\CONLLU}  format; this makes it fully compatible with the Universal Dependencies format. As a result, the resources collected for the {\UA} can also be used by the Universal Dependencies community. 
The `exploded' format is also based on the {\CONLLU}  format, but  instead of putting all information in the \CODE{Misc} column, it uses separate columns to accommodate different types of anaphoric information. 
The format has a focus on the {\NLP} community, to make it easy to interpret by humans and systems for anaphora resolution. 
The Universal Anaphora scorer currently supports the `exploded' format, but an extension supporting the `compact' format has been developed for the 2022 {\CRAC}-CorefUD shared task on Multilingual Coreference Resolution.\footnote{\url{https://ufal.mff.cuni.cz/corefud/crac22}}

% Two inter-convertible physical implementations  of the format have been defined:

% \begin{itemize}
%     \item An `exploded' version 
%     %(\UAEXPLODED) 
%     in `{\CONLLU} Plus' format, i.e, with additional columns for the separate layers  discussed above.
%     The format for these columns is based on the format defined for {\CONLL} and extended in {\CRAC}. 
%     This is the format used by the current version of the Universal Anaphora scorer and for the 2021 {\CODICRAC} shared task.
%     \item A 'compact' version %(\UACOMPACT) 
%     with all anaphoric information stored in the \CODE{Misc} column of the basic {\CONLLU} format.
%     This format  is used for documents to be included in  the {\UD} distribution.
%     % Two proposals in this direction have been put forward, by Amir Zeldes and by the Prague group.
% \end{itemize}

% \subsection{The CRAC 2018 Shared Task} 

% The more general types of anaphoric reference just discussed are now routinely annotated in a number of corpora, 
% including %, e.g., 
% {\ANCORA} \CITE{recasens&marti:LRE10}, 
% {\ARRAU} \CITE{uryupina-et-al:NLEJ}, 
% {\GNOME} \CITE{poesio:ACL-discanno04}, 
% {\GUM} \CITE{Zeldes2017}, 
% {\ISNOTES} \CITE{markert-et-al:ACL2012}, 
% the Prague Dependency Treebank \CITE{nedoluzhko:LAW13}, and 
% {\TUBADZ} \CITE{versley:ROLC08}.
% (See  \CITEA{poesio-et-al:ana-book-corpora} for a more detailed survey and \CITEA{nedoluzhko-et-al:21:CorefUD} for a more recent, extensive update.)

% Some of these resources are of a sufficient size to support shared tasks. 
% In particular, the {\ARRAU} corpus was used as the dataset for the Shared Task on Anaphora Resolution with {\ARRAU} in the {\CRAC} 2018 Workshop \CITE{poesio-etal-2018-anaphora}. 
% That shared task was articulated around three tasks: identity coreference (including identification of non-referring expressions), 
% bridging references, 
% and discourse deixis. 
% The organization of the shared task resulted in the development of an extended version of the Coreference Reference Scorer \CITE{pradhan-etal-2014-scoring}, which also scores non-referring expressions. 
% Separate scorers were developed for bridging reference resolution, carrying out both mention-based evaluation and entity-based evaluation of bridging references, as done by \CITEA{hou-et-al:CL18}, 
% and for discourse deixis, based on \CITEA{kolhatkar&hirst:EMNLP14}.
% The present shared task was modeled on that.

% \subsection{Universal Anaphora} 

% In order to  enable further progress in the empirical study of anaphora by coordinating the many existing efforts to annotate not just identity coreference, but all aspects of anaphoric interpretation from identity of sense anaphora to bridging to discourse deixis; and not just for English, but all languages, the \NEWTERM{Universal Anaphora} ({\UA}) initiative was launched in 2020.\footnote{\url{https://universalanaphora.github.io/UniversalAnaphora/}}
% Progress so far includes a first proposal concerning the range of phenomena to be covered, as well as a survey of the range of existing anaphoric annotations and a proposal for a markup format extending the {\CONLL}-U format developed by the \NEWTERM{Universal Dependencies} initiative\footnote{\url{https://universaldependencies.org/}} with mechanisms for marking up the range of anaphoric information covered by {\UA}.
% % Crucially, a scorer able to evaluate all types of anaphoric reference in the scope of the proposal was also developed, which we used in this shared task.
% % The scorer is briefly discussed in Section \ref{sec:task:scorer}.

