The Data Ring: Community Content Sharing

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The Data Ring Community Content Sharing

• Serge Abiteboul (INRIA)
• Alkis Polyzotis (UC Santa Cruz)

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Data Sharing Communities
Data sharing community a group of users that
share and query information within some domain

• Examples UCSC genome browser, SwissProt, Flickr
• Interesting data management problem
• Shared information is heterogeneous
• Data is distributed and dynamic
• Lack of central administration
• Users are not database savvy

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The Data Ring

• P2P middleware system that provides
• Monitoring
• Querying
• and other database-like services over the
  distributed information
• Main goal simplicity of use

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Data abstraction in the data ring

• Topological layer
• Physical layer
• External layer

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Data abstraction in the data ring
Topological Layer

• Declarative query services
• Data and query model based on XML

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Data abstraction in the data ring
Physical Layer

• Basic service is distributed query evaluation
• Comprises the overlay network (DHT), physical
  access structures (indices, replicas, views), and
  the catalog.

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Data abstraction in the data ring
External Layer

• Provides semantically richer data models

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Data abstraction in the data ring

• Our focus is on the topological and physical
  layer
• External layer is equally important and an active
  research area

Topological Layer
Physical Layer
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Thesis 1 formalism for distributed XML data and
queries
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Distributed XML data and queries

• What made the relational model successful
• A logic for describing tables
• An algebra for query optimization
• We need the equivalent for trees in a distributed
  context
• A logic for describing distributed XML data
• An algebra for optimizing distributed XML queries

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Desiderata for description logic

• Seamless transition between data and services
• Important for loose data integration
• Support for XML streams
• Streams are essential for subscription services
• They are also necessary to support recursion

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Starting point AXML

• AXML XML tree with embedded web service calls
• Seamless transition between intentional and
  extensional data
• Provides a simple mechanism for loose data
  integration
• Core concept XML streams
• A web service call returns a stream of elements
• Support for both push and pull semantics

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Desiderata for algebra

• Be amenable to rewrites
• Capture the topology of distributed computation
• Allow seamless transition between logical and
  physical state
• Plans may need to be re-optimized in mid-flight
• It may be necessary to perform partial
  optimization
• Error recovery

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A proposal based on AXML

• A distributed plan is a workflow of web services
  which is exactly a AXML tree
• Components
• An encoding of distributed plans in AXML
• Rewrite rules
• A nice bonus plans can be readily exchanged
  between nodes

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Disclaimer

• AXML is a starting point, not a panacea
• Bottom line we need formalisms for distributed
  XML queries

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Thesis 2 autonomic administration
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Autonomic administration

• Users are not database experts
• Typically, scientists with computer experience
• Users are averse to too many knobs
• No central authority that is responsible for
  administration
• Autonomic administration is a necessity -- not a
  gadget

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Facets of autonomy

• Self-monitoring
• Self-tuning
• Self-healing

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Some issues

• System integration
• Distribution
• On-line tuning
• Pro-active tuning

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Distributed vs. local tuning

• Distributed tuning
• Based on the global workload
• Catalog organization, replication
• Local tuning
• Based on local workload
• Physical design tuning

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Data activation for files

• A large portion of the data is expected to be in
  files
• We need to develop query processors for data
  residing in files
• File activation optimize access to the file
  based on the local workload
• E.g., instantiate an index on file contents or
  materialize a relational view
• Local tuning is essential in this context