## 2 Related Works
### Action Grouping  
The defined actions and relative properties are shown in Table 3. As reported, not all the actions have the same duration, alert level or movement type. Considering these characteristics, we have implemented a conceptual grouping that resulted in three different action groups. The identified action characteristics are the following: \"Long\" property means that actions actually can be performed in a long range of time, vice versa \"Short\" suggests that the actions can be executed quickly in a small amount of time. \"Warning\" property denotes actions that might represent a potential warning situation for the subject, the opposite \"Common\" represents common actions that do not show potential danger situations. \"Movement\" reports actions that need a partial or fully relevant body movements, its opposite \"Static\" means all actions that required a minimum displacement and body movements. Starting from datasets that provide the requested actions, we created three different groups of actions: Status, Alerting and Daily-life.  
Status represents all possible poses that a subject can reach, typically are the final state reached after a movement action, in addition we insert into this group _Walking_ and _On the floor_ that present more common characteristics with the group's actions. This group is composed of the following classes: _Seated_, _Standing_, _Lying_, _On the floor_ and _Walking_.  
Alerting contains actions that need to be monitored due to potentially representing alerting or helping situations for the subject, included actions are: _Touching head_, _Touching back_, _Touching torso_, _Touching neck_, _Vomiting_, _Coughing/sneezing_, _Waving hands_, _Exercising_ and _Falling_. In this group we also  
\begin{table}
\begin{tabular}{l c c c c|c c c} \hline \hline  & \multicolumn{6}{c}{**Characterastic**} \\ \hline  & \multicolumn{2}{c|}{**Duration**} & \multicolumn{2}{c|}{**Type**} & \multicolumn{2}{c}{**Position**} \\ \hline
**Actions** & **Long** & **Short** & **Warning** & **Common** & **Movement** & **Static** \\ \hline Drinking & ✓ & & & & ✓ & & \\ Eating & ✓ & & & ✓ & & \\ Exercising & ✓ & & & & ✓ & & \\ Falling & & ✓ & ✓ & & ✓ & \\ Walking & ✓ & & & ✓ & ✓ & \\ Lying & ✓ & & & & & ✓ \\ On the floor & ✓ & & ✓ & & ✓ & ✓ & ✓ \\ Reading & ✓ & & & ✓ & & & \\ Seated & ✓ & & & ✓ & & ✓ \\ Coughing/sneezing & & ✓ & ✓ & & ✓ & ✓ & \\ Standing & ✓ & & & ✓ & & ✓ \\ Touching back & & ✓ & ✓ & & & & \\ Touching head & & ✓ & ✓ & & & & \\ Touching neck & & ✓ & ✓ & & & \\ Touching torso & & ✓ & ✓ & & & \\ Using phone & ✓ & & & ✓ & & \\ Using laptop & ✓ & & & ✓ & & \\ Vomiting & ✓ & ✓ & ✓ & & ✓ & \\ Waiving hands & ✓ & ✓ & ✓ & & ✓ & \\ Dressing/undressing & ✓ & & & ✓ & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Defined actions of interest, with the corresponding characteristics.  
inserted _Exercising_ as a movement action class, because it shares common characteristics with other actions of the group.  
The last group, Daily-life, contains actions that can be performed in a common relaxing indoor context (typically daily life actions), which for this reason have been grouped together. The group includes: _Drinking, Eating, Reading, Using phone, Dressing/undressing_.  
The result of actions grouping and the contribution of each selected datasets are shown in Table 4.