Context is acquired by means of different sensors that gather
pieces of context information and supply the information for
interpretation and utilisation in an application [7, 13]. Two
types of sensors exist: physical and logical context sensors
[20, 22]. Physical sensors are sensors that detect context
information by the use of some form of a physical electronic
device [16, 20]. A well-known example of a physical context
sensor is the Global Positioning System (GPS) sensors (or
receiver) that are used to detect location coordinates [20].
GPS receivers work as stand-alone devices or sometimes the
receivers can be installed within a device, for example,
iPhone smart phones have built-in GPS receivers