IMMoA 2013

Semantic trajectory is a relatively recent concept developed to flexibly represent the history of locations of an entity moving continuously or nearly continuously in a reference space (i.e., trajectory). The key idea is to supplement the geometric representation of a trajectory - usually called raw trajectory - with thematic information describing application-dependent, time-varying features of the entity's movement. For example semantic trajectories can be used to describe the sequence of points of interest visited by tourists in a city, or the sequence of transportation means used by inviduals traveling in an urban setting for work or leisure. In semantic trajectories, single positions or sequences of positions inside a trajectory can be semantically annotated. This makes possible a fine-grained description of the behaviour of the moving object. The notion of semantic trajectory, however, opens up a number of issues. For example semantic trajectories magnify the risk to privacy because behavior information on individuals is explicitly extracted and represented in a machine-readable form, and therefore can be used within information processing applications and easily revealed to third parties. For this reason, semantic trajectories and privacy may clash. Moreover, the notion of semantic trajectory, while extensively investigated at conceptual level, still lacks an operational and rigorous definition. In particular it is still open to the problem of specifying how to handle and query large amounts of semantic trajectories so as to make this concept usable in real, data intensive mobile applications. In this presentation, I will discuss on-going research on these issues and emphasize the evolution of the notion of moving object.