Semantic Overlay Networks for P2P Systems

1
Semantic Overlay Networksfor P2P Systems

• Arturo Crespo and Hector Garcia-Molina

2
Motivation and Related Work

• Partition the P2P network into several thematic
  networks
• Queries for a content will not reach nodes
  without such content
• Flooding in smaller networks with smaller TTL (or
  more results with same)
• Edutella, Hypercup peers with similar content
  connect to the same SuperPeer

3
Node partitioning

• When does a node belong to SON A?
• When it contains a piece of type A
• When it contains more than x pieces of type A
• Less nodes per SONgtmore results sooner
• Less SONs per nodegtless connections
• As in DBFS, coverage problem

4
SON Classification

• Classification must provide
• Load-balance
• Each category has similar number of nodes
• Each node belongs to a small number of categories
• Easy and accurate way to classify a document

5
Statistics

• Classification from All Music Guide based on
  music style (26 styles without and 255 styles
  with substyles)
• Traces from 1800 Napster nodes
• Classifications on decade and tone provide worse
  results

6
Statistics of styles

• A node belongs to a style if it has 1 document
• 24 of the nodes belong to one style
• 90 nodes belong to up to eight
• 14 styles with 200 to 400 nodes
• 2 styles with 1000 to 1200 nodes
• 1 style with 1600 to 1800 nodes

7
Statistics of substyles

• 18 of the nodes belong to one substyle
• 90 nodes belong to up to 30 styles
• 87 of substyles with less than 400 nodes

8
Statistics of document classification

• Classification based on the All Music Guide
  database
• Reasons of failure
• Filename format
• All documents not songs
• Misspellings
• Database not complete
• 25 of documents classified incorrectly
• 4 of nodes classified incorrectly

9
Layered SONs

• Styles and substyles
• Minimum required percentage (or number) of
  documents of type A to join SON A
• May not be able to join a substyle but may join a
  style
• Nodes belonging to a substyle, do not join the
  parent style

10
Searching

• A document is classified to belong to (sub)style
  A
• Search all substyles of style A SONs
• Search (sub)style A
• Search a higher level SON
• Until we get enough results
• (How do we locate each SON?)

11
Results

• Acyclic graphs, to measure effect of msgs to
  nodes without such content
• To get half the documents that match a query
• Layered SONs 461 msgs
• Gnutella 1731 msgs