Towards a Formal Model of Context Awareness

Mikkel Baun KjærgaardJonathan Bunde-Pedersen

Department of Computer ScienceUniversity of Aarhus

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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.

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Example

Pervasive Healthcare– Context information types

• Personal Status• Activities• Location• Staff• Patients

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Motivation

  Contextual information

  Context-aware applications

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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?

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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.

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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.

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Example

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Example

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Example

  1: out{*}  2: out{Person&Status&Entity}  3: in{Person} Doctor  4: in{Status} NotBusy  5: in{Person&Status&Location&~Entity} ?

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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.

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Extensions capabilities

  Navigation

– Multiple contexts– Simple Boolean expressions– Wildcard name

  Observability– Coenter / Coexit

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Defining semantics

  Ambient like– Example of a simple in-rule

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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?

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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.

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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.