\section{MOBA competitive games}
In this section, we will dive into the topic of MOBA competitive games. We will introduce and explain the general idea and the goals that each team strives to achieve. We will then recall the important inner workings of MOBA games such as economy, objectives, roles, tactics, general strategy, and most importantly itemization choice. The game on which this thesis focuses is League of Legends, although it is important to mention that the general idea of this work holds for most MOBA games, and simply using a different dataset of champions, items, and stats while using the same techniques for item recommendation would work in a similar fashion.

\subsection{Definition}
Multiplayer Online Battle Arena (MOBA) games represent a distinct genre of real-time strategy games where two teams of players compete on a typically symmetrical map, conventionally divided into three main lanes. Each player controls a unique character—referred to as a champion or hero, with specific roles, abilities, and responsibilities. The main goal of each team is to destroy the main structure of the enemy team, which lies in the deepest point of the base of each team. In order to destroy this structure, now referred to as \textbf{nexus}, players must destroy all secondary structures on at least one of the three main lanes. A player might encounter a variety of entities scattered across the map.

\begin{figure}[h]
    \centering
    \includegraphics[width=.5\textwidth]{images/moba_map.png}
    \caption{A typical layout of MOBA map}
    \label{img:mobamap}
\end{figure}

\subsection{In-game economy}

Economy is one of the main topics discussed in relation to MOBA. Team's economy does not only dictate the style of their play, whether is aggressiveness, map control, or risk taking, but it highly affects their gameplay possibilities and probability of victory. The main goal might be to destroy the enemy nexus, but in order to do so, teams have to lay strong foundation by building up their economy better than the opposing team. There are various means of gathering so-called net worth. There are two main resources in relation to economy, gold and experience. Every player controlled character (champion) can gain experience points and therefore increase his level. With each level a player is able to upgrade his champion's ability of his choosing. However, there is only a certain amount of experience points a player can amass, therefore there is maximum level which his champion can become. In this thesis we focus on in game items, which are bought for gold, so the topic of experience points only proves as an introduction into the inner workings of MOBA games.

\subsection{Base statistics}

The in game world in MOBA games is composed of base statistics.
When referring to units (such as champions), a statistic measures the power of an unmodified basic attribute or capability. For example: how durable they are; how fast they are able to move; how quickly they are able to perform basic attacks; etc. A base effect (e.g. how much damage an ability deals) that increases in strength by a statistic is said to "scale with" or "scale off of" that statistic. Scaling type can either directly or indirectly influence the champion's capabilities, and often heavily correlates to the champion's design. Statistics define a champion's numerical strength at various stages of the game or a fight, but not necessarily their overall strength — nevertheless, big differences in statistics also mean a substantial difference in the way different champions and champion classes interact with each other on the battlefield, as well as influence the game. 

There are 23 types of champion statistics divided into 3 different categories: Defensive, Offensive, and Utility. In the list below, only the basic attribute of each statistic is presented. In League of Legends, modified attacks, abilities, items, and runes, may freely scale off of any and/or multiple statistics (and sometimes other effects), whether in their damage, defense, cooldown, or any other attribute.\\

Defensive statistics:
\begin{itemize}
    \item Health [HP]: A champion dies when their health is reduced to zero. Some abilities and effects may scale off of your own, on your ally's, or on a target enemy's: current, bonus, missing, or maximum health.
    \item Health regeneration [HP5]: The amount of health a champion passively restores per 5 seconds.
    \item Heal and shield power: Increases the strength of healing or shielding effects on yourself or allies.
    \item Armor [AR]: Reduces (mitigates) the amount of physical damage taken, thus increasing a champion's effective health against physical damag
    \item Magic resistance [MR]: Reduces (mitigates) the amount of magic damage taken, thus increasing a champion's effective health against magic damage.
    \item Tenacity: Reduces the duration of most hostile crowd control effects/disables by a percentage. Stacking multiple sources of tenacity has diminishing returns. Disables cannot be reduced to under 0.5 seconds.
    \item Slow resist: Reduces the strength of incoming hostile slows (movement speed reductions). The reduction is a percentage of the slow's strength.
\end{itemize} \\

Offensive statistics:
\begin{itemize}
    \item Attack speed [AS]: The number of basic attacks your champion is allowed to perform per second.
    \item Attack damage [AD]: One of the two main offensive statistics, along with Ability Power. Unmodified basic attacks deal exactly this amount of damage.
    \item Ability power [AP]: One of the two main offensive statistics, along with Attack Damage.
    \item Critical strike chance: Denotes the chance that a basic attack will critically strike. Certain abilities can also critically strike for modified damage.
    \item Critical strike damage: Denotes the damage dealt when a basic attack critically strikes. Abilities that can critically strike usually also benefit from critical strike damage.
    \item Armor penetration: When applying physical damage to an enemy, ignores a part of their armor in the damage calculations. Armor penetration can be either flat (lethality) or percentage-based. The target's armor is unchanged.
    \item Magic penetration: When applying magic damage to an enemy, ignores a part of their magic resistance in the damage calculations. Magic penetration can be either flat or percentage-based. The target's magic resistance is unchanged.
    \item Life steal: How much health a champion restores, as a percentage of the post-mitigation damage dealt by basic attacks and on-hit effects.
    \item Physical vamp: How much health a champion restores, as a percentage of all physical damage dealt. Physical vamp is only 33\% as effective when dealing area damage or pet damage.
    \item Omnivamp: How much health a champion restores, as a percentage of all damage dealt. Omnivamp is only 20\% as effective against non-champions.
\end{itemize}



 
    
    
    
    

