– This class represents a specific act that is performed by the members (i.e. users) of the crowd. An action can be cognitive or physical. For instance, the comparison of two images involves a cognitive action from user.
– This class defines the human capability that is necessary for performing a task. Capability is defined as the ability of humans to do things in terms of both the capacity and the opportunity.
– This class represents a specific place where a user is or will be physically present. This type of capability enables crowd contributions that are related to a physical place such as participatory sensing.
– This class defines the unit of work, resulting in a desired outcome, that is assigned to the members of the crowd. A task may require one or more actions to produce a specific outcome. Therefore a task at the lowest level is composed of a set of actions. This class has composition relationship with itself because complex tasks can be broken down into small simple tasks.