Blackboard Style and
Blackboard Platforms
CPSC 410
Problem
In traditional programming:
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We prefer to look at each component as a black box.
In concurrent and distributed programming:
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We need mechanisms for controlling interactions between the
autonomous components
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“Come and go as they please”
Turn on/off
Connect/Disconnect
Plug in/Plug out
Fail/Crash
Fallacies of distributed computing
 The
network is reliable.
 Latency is zero.
 Bandwidth is infinite.
 The network is secure.
 Topology doesn't change.
 There is one administrator.
 Transport cost is zero.
 The network is homogeneous.
http://en.wikipedia.org/wiki/Fallacies_of_distributed_computing
Blackboard Architecture
Active
Data
Storage
Agent A
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Components
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Agent C
Agent B
Active Data Storage
Agents (aka Knowledge Sources)
Connectors
Data publication
Data subscription
publish/subscribe
Lunar lander in BB style
Blackboard example
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See (and clone) http://github.com/UBCCS410/PublicMessenger
Very simple demonstration using sockets.
Connectors: Blackboard Architecture
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Data subscription
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Agents can register interest in data using patterns (somewhat
like queries)
Subscription remains in affect until data is available
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Provides temporal decoupling
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Critical difference compared to database queries
Simplifying synchronization
Data publication
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All communication between agents done by modifying active
data storage
Similar to traditional database updates except also trigger
notification to subscribers
Components: Blackboard Architecture
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Active Data Storage
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Database + Coordination System
Stores data
Also tracks which agents are interested in what data
Notifies agents when data is available
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Pushes notifications to agents
Agent clients don’t need to poll
Agent
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“Clients” of the blackboard
Different from Client/Server
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Agents contain all intelligence in the system
There is no application layer server code
aka Knowledge Sources
Blackboard Example: CMU Robotics
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“The CMU Navlab group builds robot cars, trucks, and buses, capable of
autonomous driving or driver assistance”
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Data Storage
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information the Robot knows of its environment
Agents
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Robot parts/sensors
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Actually software components that control robot parts
Robot parts share data and react to changes of environment
… But parts do not directly depend on each other
… Some parts can fail or be destroyed without compromising
the entire robot
Example:
Production
-line
scheduling
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http://www.ri.cmu.edu/pub
_files/pub2/sadeh_koniecp
ol_norman_1998_1/sadeh
_koniecpol_norman_1998
_1.pdf
Contrast to other Arch. Styles
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Just to point out a few differences…
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Virtual Machine
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BB generally has no server-side application functions
Dataflow
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BB does not focus on abstraction
Client/Server
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No preplanning, support autonomous agents
BB has bi-directional sending of data
Compared to all 3 above
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BB has star-topology
Blackboard Platforms
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Programming technology to implement
blackboard-based systems
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Linda
JavaSpaces
GigaSpaces
Apache River/Jini
Supplanted by Web Services and Service Oriented
Architectures (next time …)
Midterm Review
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Format:
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45 minutes
Closed books
~25% multiple choice/T&F
~25% short answer
~50% diagrams, paragraphs (note form is ok)
Topics:
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AOSA presentations up to today
Lectures up to today minus Oct 3
Readings not marked optional