Keyword Searching and Browsing in Databases using BANKS

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Keyword Searching and Browsing in Databases using
BANKS

• Gaurav Bhalotia, Arvind Hulgeri,
• Charuta Nakhe,
• Soumen Chakrabarti, S. Sudarshan
• I.I.T. Bombay

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Motivation

• Keyword search of documents on the Web has been
  enormously successful
• Simple and intuitive, no need to learn any query
  language
• Database querying using keywords is desirable
• SQL is not appropriate for casual users
• Form interfaces cumbersome
• Require separate form for each type of query
  confusing for casual users of Web information
  systems
• Not suitable for ad hoc queries

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Motivation

• Many Web documents are dynamically generated from
  databases
• E.g. Catalog data
• Keyword querying of generated Web documents
• May miss answers that need to combine information
  on different pages
• Suffers from duplication overheads

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Examples of Keyword Queries

• On a railway reservation database
• mumbai bangalore
• On an e-store database
• camcorder panasonic
• On a book store database
• sudarshan databases

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Differences from IR/Web Search

• Related data split across multiple tuples due to
  normalization
• E.g. Paper (paper-id, title, journal),
  Author (author-id, name) Writes
  (author-id, paper-id, position)
• Different keywords may match tuples from
  different relations
• What joins are to be computed can only be decided
  on the fly
• Cites(citing-paper-id, cited-paper-id)

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Connectivity

• Tuples may be connected by
• Foreign key
• Implicit links (shared words), etc.
• Tuples belonging to the same relation
• Would like to find sets of (closely) connected
  tuples that match all given keywords

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Basic Model

• Database modeled as a graph
• Nodes tuples
• Edges references between tuples
• foreign key, other kind of relationships
• Edges are directed.

MultiQuery Optimization
paper
BANKS Keyword search
writes
S. Sudarshan
Prasan Roy
Charuta
author
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Answer Example
Query sudarshan roy
paper
MultiQuery Optimization
writes
writes
author
author
S. Sudarshan
Prasan Roy
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Edge Directionality

• Some popular tuples are connected to many other
  tuples
• E.g. Students -gt departments -gt university
• Popular tuples would create misleading shortcuts
  from every tuple to every other
• E.g. every student would be closely linked with
  every other student via the department/university
• Solution define different forward and backward
  edge weights
• Forward edges In the direction of the foreign
  key reference

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Edge Weight

• Weight of forward edge based on schema
• e.g. citation link weights gt writes link weights
• Weight of backward edge indegree of edges
  pointing to the node

1
1
1
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Edge Weight Scaling

• Problem Some backward edges have unduly large
  weights
• Scale edge weights by using log(1raw-edgeweight)
• total-edge-weight ? edge-weights
• Edge score E 1 / total-edge-weight

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Node Weight

• Nodes have prestige weights too
• Observation nodes with intuitively greater
  prestige tend to have greater indegree
• Set node weight indegree
• Problem Nodes with many in-edges result in
  skewed answers
• Subdue extreme node weights by using
  log(1indegree)
• Node score N root-node-weight ?
  leaf-node-weights

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Combining Scores

• Problem how to combine two independent metrics
  node weight and edge weight
• Normalize each to 0-1
• Combine using weighting factor ?
• Additive (1- ?) E ? N
• Multiplicative E N?
• Performance study to compare alternatives and to
  find reasonable values for ?

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The BANKS Answer Model

• Query set of keywords k1, k2, .., kn
• Each keyword ki matches set of nodes Si
• Answer rooted, directed tree connecting nodes,
  with one node from each Si
• Root node(also referred to as Information Node)
  has special significance, may be restricted to
  some relations
• E.g. relations representing entities, not
  relationships
• May include intermediate nodes not in any Si and
  hence a Steiner tree.
• Multiple answers
• Ranking based on proximity prestige

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Finding Answer Trees

• Computation of minimum weight Steiner
• Trees NP complete
• Backward Expanding Search Algorithm
• Intuition find vertices from which a forward
  path exists to at least one node from each Si.
• Run concurrent single source shortest path
  algorithm from each node matching a keyword
• Create an iterator for each node matching a
  keyword
• Traverse the graph edges in reverse direction
• Output a node whenever it is on the intersection
  of the sets of nodes reached from each keyword

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Finding Answer Tress

• For each vertex visited, maintain a nodelist v.Li
  for each search term ti.
• Update the ith nodelist when the search starting
  from a vertex u?Si reaches the vertex v.
• The new result tress produced correspond to the
  nodelists u ? v.Lj
• ij

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Backward Expanding Search
Query sudarshan roy
S. Sudarshan
Prasan Roy
authors
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Result Ordering

• Answer trees may not be generated in relevance
  order
• Solution
• Best-first search across all iterators, based on
  path length
• Output answers to a buffer
• Eliminate duplicates Isomorphic Trees
• Output highest ranked answer from buffer to user
  when buffer is full

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THE BANKS SYSTEM

• BANKS provides keyword search coupled with
  extensive browsing facilities
• Schema browsing data browsing
• Graphical display of data
• Implemented using Java servlets
• Keyword search response times typically 1 to 3
  seconds on
• DBLP database with 100,000 tuples/300,000 edges
• P3 600 MHz, 512 MB RAM
• Try it out at www.cse.iitb.ac.in/banks/

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The BANKS Architecture

• Connects to any database using JDBC
• JDBC metadata features used to provide schema
  browsing
• No programming needed for customization
• Minimal preprocessing of database to create
  indices and give weights to links
• Extensive set of browsing features

BANKS
User
HTTP
JDBC
Web Server Servlets
Database
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Browsing Features

• Hyperlinks are automatically added to all
  displayed results
• Template facilities to do a variety of tasks
• Browsing data by grouping and creating crosstabs
• e.g., theses grouped by department and year
• Hierarchical views of data
• Nested XML style, even on relational data
• Graphical displays
• Bar charts, pie charts, etc

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Example of Browsing in BANKS
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BANKS Query Result Example

• Result of Soumen Sunita

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Anecdotes

• Mohan
• Returns C. Mohan at top based on prestige (number
  of papers written)
• Transaction
• Returns Jim Grays classic paper and textbook as
  top answers based on prestige (number of
  citations)
• Sunita Seltzer
• No common papers, but both have papers with
  Stonebraker system finds this connection

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Effect of Parameters

• Log scaling of edge weights worked well
  
• (1- ?) E ? N versus E N? -- made little
  difference
• Best with ? .2 (subdue node weights but not
  entirely)

EdgeLog
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Related Work

• DataSpot (DTL)/Mercado Intuifind VLDB 98
• Based on patent by Palmon (filed 1995, granted
  1998)
• Similar answer model to ours
• Differences our model of backward link weights
  and prestige
• Proximity Search VLDB98
• Different model of proximity
• No edge weights, prestige, different evaluation
  algorithm
• Information units (linked Web pages) WWW10
• No directionality, only studied in Web context
• Microsoft DBExplorer
• No ranking, based on SQL generation
• Addresses efficient construction of text indexes

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Some Extensions to the BANKS

• Searching for similar results Template Search
• define the notion of similarity between two
  result trees
• perform the restricted search
• Efficiently handling meta-data queries
• starting the search from each of the tuples in a
  table is too costly

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Template Search

• Feedback in terms of result tree
• Type of a result tree defined in terms of
• type of nodes
• the table to which the node belongs
• type of edges
• the type of nodes which it connects
• the link information e.g. cites and cited
  link between two papers.
• Which nodes to start the search from
• only the chosen nodes
• all the nodes corresponding to a particular
  keyword

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Template Search

• Start the backward search only from allowed set
  of nodes
• Follow the edges as defined by the result type
• Example Consider Query sudarshan database
• Two types of results for above query
• papers written by professor sudarshan
• papers cited by papers written by professor
  sudarshan
• Two result types distinguished by whether to
  follow the cites/cited link from a paper node.

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Metadata Keyword Queries

• Metadata keywords match all the tuples of
• a relation.
• Too costly to start the search from each of
• the tuples of a table
• First cut approach start the forward search from
  the information node for the non-metadata
  keywords
• selectively choose the nodes from where to
• start the forward search

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Example of Metadata Query

• Consider the query sudarshan paper

writes table nodes
To paper table
(forward search)
sudarshan
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Conclusions and Future Work

• The next big wave keyword searching and browsing
  of databases?
• Future work
• Keyword queries on XML
• Disambiguating queries by selecting
• Nodes G.W.Bush Bush Jr or Bush Sr
• Tree structure coauthors or cites
• Boolean queries, stemming, thesaurus
• Metadata column/relation names

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Thank You