\section{Datasets}\label{datasets}

In this section we describe the datasets we used in our experiments.

\begin{figure*}[t!]
  \centering
  \subfigure[MMA dataset.] { \epsfig{file=figuras/dados_mma.eps,width=.48\textwidth} }   
  \label{mma_dataset}
  \subfigure[Tennis dataset.] { \epsfig{file=figuras/dados_tenis.eps,width=.48\textwidth} }
  \label{tennis_dataset}
  \caption{Number of confronts and athletes through time.}
\end{figure*}

\subsection{MMA}\label{esporte}
\indent

As far as we know, there is no publicly available dataset with results of MMA fights. To obtain structured data of fight results one has to look for websites that make this kind of data available and use a  wrapper~\cite{laender2002} to extract it. The main and most complete site related to MMA in terms of fight results is Sherdog\footnote{http://www.sherdog.com/}. However, Sherdog does not make available information about the category of the fights, only the fighters' main categories. As fighters may compete in distinct categories at different points in time and we wanted to compare rankings obtained from fights of each category, we could not use this data.

Instead, we used data from the FightMetrics site\footnote{http://fightmetric.com/} which also makes available the results of the most important fights in the main MMA events around the world. Although it covers less fights than Sherdog, it shows detailed information of each match, including the category of each one. Moreover, FightMetrics has also a cleaner and more structured interface which facilitates the creation of a wrapper for data extraction.
Table~\ref{data_summary} summarizes the data collected.

\begin{table}[h]
\caption{Summary of the extracted data.}
\captionspace
\centering
\begin{tabular}{|l|c|}
\hline Number of fighters & 1838 \\
\hline Number of fights & 3648 \\
\hline Number of organizations & 59 \\
\hline
\end{tabular}
\label{data_summary}
\end{table}

Figure \ref{mma_dataset}(a) shows the number of MMA fights and fighters through time. As we can see, only recently MMA has started having a large number of matches per year. This shows that this is a new and growing popular sport.

\subsection{Tennis}\label{rede}

We collected data about tennis matches from the website of the Association of Tennis Professionals (ATP)\footnote{http:\/\/www.atpworldtour.com}. We collected all matches played by professional tennis
players from January 1968 to October 2010, summing up to a total of 378566 matches. Table~\ref{data_summary_tennis} summarizes the data collected.

Figure~\ref{tennis_dataset}(b) shows the number of matches and tennis players through time. As we can see, tennis is already a consolidated sport, presenting a much larger number of confronts per year than MMA. 


\begin{table}[h]
\caption{Summary of the extracted data.}
\captionspace
\centering
\begin{tabular}{|l|c|}	
\hline Number of players & 13703 \\
\hline Number of matches & 378566 \\
\hline
\end{tabular}
\label{data_summary_tennis}
\end{table}
