Towards a Formal Model of Context Awareness

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Towards a Formal Model of Context Awareness

• Mikkel Baun Kjærgaard
• Jonathan Bunde-Pedersen
• Department of Computer Science
• University 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

• Context-aware applications

• Contextual information

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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 outPersonStatusEntity
• 3 inPerson Doctor
• 4 inStatus NotBusy
• 5 inPersonStatusLocationEntity ?

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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.