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Towards a Formal Model of Context Awareness
Mikkel Baun KjærgaardJonathan Bunde-Pedersen
Department of Computer ScienceUniversity of Aarhus
May 2006 Mikkel Baun Kjærgaard 2
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 2006 Mikkel Baun Kjærgaard 3
Example
Pervasive Healthcare– Context information types
• Personal Status• Activities• Location• Staff• Patients
May 2006 Mikkel Baun Kjærgaard 4
Motivation
Contextual information
Context-aware applications
May 2006 Mikkel Baun Kjærgaard 5
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 2006 Mikkel Baun Kjærgaard 6
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 2006 Mikkel Baun Kjærgaard 7
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 2006 Mikkel Baun Kjærgaard 8
Example
May 2006 Mikkel Baun Kjærgaard 9
Example
May 2006 Mikkel Baun Kjærgaard 10
Example
1: out{*} 2: out{Person&Status&Entity} 3: in{Person} Doctor 4: in{Status} NotBusy 5: in{Person&Status&Location&~Entity} ?
May 2006 Mikkel Baun Kjærgaard 11
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 2006 Mikkel Baun Kjærgaard 12
Extensions capabilities
Navigation
– Multiple contexts– Simple Boolean expressions– Wildcard name
Observability– Coenter / Coexit
May 2006 Mikkel Baun Kjærgaard 13
Defining semantics
Ambient like– Example of a simple in-rule
May 2006 Mikkel Baun Kjærgaard 14
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 2006 Mikkel Baun Kjærgaard 15
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 2006 Mikkel Baun Kjærgaard 16
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.