\usepackage{url}

\numberofauthors{8} %  in this sample file, there are a *total*

filtering.

We base this analysis on the TREC-KBA 2013 dataset%

\footnote{\url{http://trec-kba.org/trec-kba-2013.shtml}}

that consists of three main parts: a time-stamped stream corpus, a set of

KB entities to be curated, and a set of relevance judgments. A CCR

system now has to identify for each KB entity which documents in the

stream corpus are to be considered by the human curator.

\subsection{Stream corpus} The stream corpus comes in two versions:

raw and cleaned. The raw and cleansed versions are 6.45TB and 4.5TB

respectively,  after xz-compression and GPG encryption. The raw data

is a  dump of  raw HTML pages. The cleansed version is the raw data

after its HTML tags are stripped off and only English documents

identified with Chromium Compact Language Detector

\footnote{\url{https://code.google.com/p/chromium-compact-language-detector/}}

are included.  The stream corpus is organized in hourly folders each

of which contains many  chunk files. Each chunk file contains between

hundreds and hundreds of thousands of serialized  thrift objects. One

thrift object is one document. A document could be a blog article, a

news article, or a social media post (including tweet).  The stream

corpus comes from three sources: TREC KBA 2012 (social, news and

linking) \footnote{\url{http://trec-kba.org/kba-stream-corpus-2012.shtml}},

arxiv\footnote{\url{http://arxiv.org/}}, and

spinn3r\footnote{\url{http://spinn3r.com/}}.

Table \ref{tab:streams} shows the sources, the number of hourly

directories, and the number of chunk files.

We build entity profiles for the KB entities of interest. We have two

types: Twitter and Wikipedia. Both entities have been selected, on

purpose by the track organisers, to occur only sparsely and be less-documented.

For the Wikipedia entities, we fetch different name variants

from DBpedia: name, label, birth name, alternative names,

redirects, nickname, or alias. 

These extraction results are summarized in Table

\ref{tab:sources}.

For the Twitter entities, we visit

their respective Twitter pages and fetch their display names. 

The collection contains a total number of 121 Wikipedia entities.

Every entity has a corresponding DBpedia label.  Only 82 entities have

a name string and only 49 entities have redirect strings. (Most of the

entities have only one string, except for a few cases with multiple

redirect strings; Buddy\_MacKay, has the highest (12) number of

redirect strings.) 

We combine the different name variants we extracted to form a set of

strings for each KB entity. For Twitter entities, we used the display

names that we collected. We consider the names of the entities that

are part of the URL as canonical. For example in entity\\

\url{http://en.wikipedia.org/wiki/Benjamin_Bronfman}\\

Benjamin Bronfman is a canonical name of the entity. 

An example is given in Table \ref{tab:profile}.

From the combined name variants and

the canonical names, we  created four sets of profiles for each

entity: canonical(cano) canonical partial (cano-part), all name

variants combined (all) and partial names of all name

variants(all-part). We refer to the last two profiles as name-variant

and name-variant partial. The names in parentheses are used in table

captions.

%Most (more than 80\%) of the annotation documents are in the test set.

The 2013 training and test data contain 68405

annotations, of which 50688 are unique document-entity pairs.   Out of

these, 24162 unique document-entity pairs are vital (9521) or relevant

(17424).

When comparing recall for vital and relevant, we observe that

canonical names are more effective for vital than for relevant

entities, in particular for the Wikipedia entities. 

%For example, the recall for news is 80.1 and for social is 76, while the corresponding recall in relevant is 75.6 and 63.2 respectively.

We conclude that the most relevant documents mention the

entities by their common name variants.

The recall for Wikipedia entities in Table \ref{tab:name} ranged from

61.8\% (canonicals) to 77.9\% (name-variants).  Table

\ref{tab:source-delta} shows how recall is distributed across document

categories. For Wikipedia entities, across all entity profiles, others

have a higher recall followed by news, and then by social.  While the

recall for news ranges from 76.4\% to 98.4\%, the recall for social

documents ranges from 65.7\% to 86.8\%. In Twitter entities, however,

the pattern is different. In canonicals (and their partials), social

documents achieve higher recall than news.

Overall, across all entities types and all entity profiles, documents

Table \ref{tab:name} summarizes the differences between Wikipedia and

Twitter entities.  Wikipedia entities' canonical representation

achieves a recall of 70\%, while canonical partial achieves a recall of 86.1\%. This is an

increase in recall of 16.1\%. By contrast, the increase in recall of

name-variant partial over name-variant is 8.3\%.

%This high increase in recall when moving from canonical names to their

%partial names, in comparison to the lower increase when moving from

%all name variants to their partial names can be explained by

%saturation: documents have already been extracted by the different

%name variants and thus using their partial names do not bring in many

%new relevant documents.

For Wikipedia entities, canonical

partial achieves better recall than name-variant in both the cleansed and

the raw corpus.  %In the raw extraction, the difference is about 3.7.

In Twitter entities, recall of canonical matching is very low.%

\footnote{Canonical

and canonical partial are the same for Twitter entities because they

are one word strings. For example in https://twitter.com/roryscovel,

``roryscovel`` is the canonical name and its partial is identical.}

%The low recall is because the canonical names of Twitter entities are

%not really names; they are usually arbitrarily created user names. It

%shows that  documents  refer to them by their display names, rarely

%by their user name, which is reflected in the name-variant recall

%(67.9\%). The use of name-variant partial increases the recall to

%88.2\%.

The tables in \ref{tab:name} and \ref{tab:source-delta} show a higher recall

for Wikipedia than for Twitter entities. Generally, at both

aggregate and document category levels, we observe that recall

increases as we move from canonicals to canonical partial, to

name-variant, and to name-variant partial. The only case where this

does not hold is in the transition from Wikipedia's canonical partial

to name-variant. At the aggregate level (as can be inferred from Table

\ref{tab:name}), the difference in performance between  canonical  and

name-variant partial is 31.9\% on all entities, 20.7\% on Wikipedia

entities, and 79.5\% on Twitter entities. 

Section \ref{sec:analysis} discusses the most plausible explanations for these findings.

In the overall experimental setup, classification, ranking, and

evaluation are kept constant. Following \cite{balog2013multi}

settings, we use

WEKA's\footnote{\url{http://www.cs.waikato.ac.nz/~ml/weka/}} Classification

Random Forest. However, we use fewer numbers of features which we

found to be more effective. We determined the effectiveness of the

features by running the classification algorithm using the fewer

features we implemented and their features. Our feature

implementations achieved better results.  The total numbers of

features we used are 13 and are listed below.

There are 3 interesting observations: 

1) cleansing impacts Twitter

2) Taking both performance (recall at filtering and overall F-score