Spatial Subscriptions in Distributed Event- Based Systems

One of the common approaches to specify locations is by indicating their spatial relationships to other, more well-known, locations. This chapter aims at analyzing the feasibility of expressing this kind of spatial relations in subscriptions of Distributed Event-based Systems (DEBSs). On one hand, the spatial relation expressions consist of various location-level abstractions, which have to be interpreted by the location models used in the systems. On the other hand, existing DEBSs are categorized by their filter models, and each category is merely capable of supporting a subset of all location models. The chapter presents ways to express different location-level abstractions by using different filter models and introduces the option of overlaying an extra mapping layer in systems to enhance their expressiveness of spatial relations in subscriptions.