Towards a Formal Model of Context Awareness Mikkel Baun Kjærgaard Jonathan Bunde-Pedersen Department of Computer Science University of Aarhus

May 2006Mikkel Baun Kjærgaard2 Motivation Pervasive computing vision: –Move computation from the desktop computer to a number of devices embedded in the environment of the user. Context-awareness –However the task of handling all these devices should not overwhelm the human user. –Therefore the devices and applications need to become aware of the context they are situated in. –The context of interest could here both be the physical, social and computational environment. Modeling Context Information –Complex A lot of different factors where some of them can only be described probabilistically. –Interwoven The different types of information depend and relate to each other in many ways.

May 2006Mikkel Baun Kjærgaard3 Example Pervasive Healthcare –Context information types Personal Status Activities Location Staff Patients

May 2006Mikkel Baun Kjærgaard4 Motivation Contextual information Context-aware applications

May 2006Mikkel Baun Kjærgaard5 Motivation Application areas –Healthcare,... –A lot of the applications are critical in some way –At build time / online validation? For interesting properties: consistency, privacy, … Formal foundation –Should be expressive enough to model complex and interwoven context-information. Goal –How can the Ambient Calculus be extended to allow us to model complex and interwoven sets of context information?

May 2006Mikkel Baun Kjærgaard6 Ambient Calculus The Ambient Calculus –deals with ambients which are tree-structured recursively defined entities. –An ambient may be situated in another ambient and itself contain ambients, and –Information between ambients may only flow between nearby ambients, i.e. parents or siblings. Modeling Context using Ambients –If context-information should be made available for an ambient it must be positioned near the ambient in the tree.

May 2006Mikkel Baun Kjærgaard7 Idea Multiple Contexts –Ambients which can be present in one or more trees. Two types of ambients –Context ambients vs. Reference ambients New capabilities which enables the reference ambients to navigate in multiple contexts.

May 2006Mikkel Baun Kjærgaard8 Example

May 2006Mikkel Baun Kjærgaard9 Example

May 2006Mikkel Baun Kjærgaard10 Example 1: out{*} 2: out{Person&Status&Entity} 3: in{Person} Doctor 4: in{Status} NotBusy 5: in{Person&Status&Location&~Entity} ?

May 2006Mikkel Baun Kjærgaard11 Extensions ambients –Context ambients Context information is represented in trees. Names of context trees are unmutable. Context ambients have limited capabilities. –Reference ambients Only one reference in a single context Reference ambients must not contain references to other reference ambients. Reference ambients are unique in the sense that all references to ambient n points to the same n. Reference ambients cannot remove themselves directly from a context.

May 2006Mikkel Baun Kjærgaard12 Extensions capabilities Navigation –Multiple contexts –Simple Boolean expressions –Wildcard name Observability –Coenter / Coexit

May 2006Mikkel Baun Kjærgaard13 Defining semantics Ambient like –Example of a simple in-rule

May 2006Mikkel Baun Kjærgaard14 Discussion Limitations –Restricts context information to a number of trees which limits the expressiveness but to a lesser degree than prior research. –Does not take probabilistic context information into account. It is important for a calculi to be able to handle such information because it is the typical output of most sensors of context information. –Is the above needed in practice?

May 2006Mikkel Baun Kjærgaard15 Discussion The present CONAWA calculus does not bridge the gap to a combined theory and systems building approach –base for simulation, verification and software prototyping –(i) Building a simulator which can interpret CONAWA descriptions –(ii) Defining a logic which make it possible to state properties which could be verified “This awarephone must never reveal my location to other people than the ones I have explicitly granted this priviledge”? –(iii) Building a code generation facility that makes it possible to build skeleton code from the models.

May 2006Mikkel Baun Kjærgaard16 Conclusion –Expressiveness of formal models of context awareness. –Here the models expressiveness should be sufficient to model complex and interwoven sets of context- information. –The CONAWA calculus was given as an example of a calculus that is a step in the direction of making such modeling possible.