BLAS: An Efficient XPath Processing System

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BLAS An Efficient XPath Processing System

• Zhimin Song
• Advanced Database System
• Professor Dr. Mengchi Liu

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Outline

• Introduction
• BLAS System
• Experimental Results
• Conclusions

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• ltProteinDatabasegt
• ltProteinEntrygt
• ltProteingt
• ltNamegt cytochrome c validatedlt/namegt
• ltclassificationgt
• ltsuperfamilygtcytochrome clt/superfamilygt
• lt/classificationgt
• lt/proteingt
• ltreferencegt
• ltrefinfogt
• ltauthorsgt
• ltauthorgtEvans, M.J.lt/authorgt
• lt/authorsgt
• ltyeargt2001lt/yeargt
• lttitlegt The human somatic cytochrome c gene
  lt/titlegt
• lt/refinfogt
• lt/referencegt
• lt/ProteinEntrygt
• lt/ProteinDatabasegt

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Introduction

• XML has complex, tree-like structure(nodes).
• Languages for Querying XML are based on path
  navigation(XPath 1).
• Given node ? Child node(Child axis)
• Given node ? Descendant node(Descendant axis)

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Introduction(cont..)

• Some techniques were already proposed in order to
  improve XPath Processing. For example, D-labeling
  which is used to efficiently handle descendant
  axis traversal.
• What about complex queries including child axis,
  branch???
• In this case P-labeling is proposed in this
  paper. It optimizes an important class of queries
  called suffix path queries.

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BLAS(Bi-LAbeling based System)

• Basic definitions
• The labeling scheme(Index generator)
• Query translator

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• Basic definitions
• BLAS a system for efficiently process complex
  queries based D-labeling and P-labeling.
• The BLAS deals with a subset of XPath queires
  consisting of
• Child axis navigation ( / )
• Descendant axis navigation ( // )
• Branches ( .. )
• The evaluation of a path expression P( P )
  returns the set of nodes in an XML tree T which
  are reachable by P starting from the root of T.
• Since P can be evaluated to retrieve a set of XML
  nodes, we use Path expression and query
  interchangeably.
• P Q if and only if P Q.
• P Q if and only if P Q

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• Basic definitions(cont..)
• Suffix path expression a path expression P which
  optionally begins with a descendant axis
  step(//), followed by zero or more child axis
  steps (/).
• Example //protein/name
• Another one /proteinDatabase/proteinEntry/protei
  n/name
• SP(n) the unique simple path P from the root to
  the node n.
• So evaluating a suffix path expression Q is to
  find all the nodes n such that SP(n) Q.

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Architecture of BLAS
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• The labeling scheme(Index generator)
• D-labeling scheme triplet ltd1,d2,d3gt for a XML
  node n(n.d1 lt n.d2) and m(m.d1ltm.d2).
• m is a descendant of n if and only if n.d1ltm.d1
  and n.d2gtm.d2.
• m is a child of n if and only if m is a
  descendant of n and n.d31m.d3.
• Let d1 and d2 for a node n be the position of the
  start tag and end tag.
• d3 is set to be the level of n in the XML tree
  which is the length of the path from the root to
  n.
• ? D-label will be represented as ltstart,end,levelgt

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• Example using D-labeling

proteinDatabase
proteinEntry
protein
reference
superfamily
//
refinfo
cytochrome c
//
year
author
Title
Select pDB.start,pDB.end,refinfo.start,refinfo.end
From pDB, refinfo Where pDB.start lt
refinfo.start and pDB.end gt refinfo.end
Evans, M.J.
2001
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• P-labeling Scheme
• It is also important to implement child axis
  navigation efficiently.
• e.g. /proteinDatabase/proteinEntry/protein/name
• Target improve / evaluation
• Focus on suffix path queries
• e.g. //protein/name

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• Assign each node a numberltp1gt, and each suffix
  path an interval ltp1,p2gt such that
• For any two suffix paths Q1 and Q2, Q1 is
  contained in Q2 if
• Q1.p1lt Q2.p1 and Q1.p2gt Q2.p2
• A node n is contained in the suffix path Q if
• Q.p1lt SP(n).p1 ltQ.p2.
• Let Q be a suffix path query. Then
• Q n Q.p1 lt n.plabelltQ.p2 when
  n.plabelSP(n).p1

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• P-labeling Construction(algorithm)
• Suppose that there are n distinct tags
  (t1,t2,.,tn).
• Assign / a ratio r0 and each tag ti a ratio ri
  such that
• r0r1r2.ri 1.
• Let ri 1/(n1).
• Define the domain of the numbers in a P-label to
  be integers in 0, m-1, here m is chosen such
  that
• mgt , where h is the longest path
  in an XML tree.
• Algorithms as follows
• Path // is assigned an interval(P-label) of lto,
  m-1gt.
• Partition the interval lt0, m-1gt in tag order
  proportional to tis ratio ri, for each path //ti
  and child axis navigations ratio r0.
• This means we allocate the intervallt0, mr0 -1gt
  to / and ltpi, pi1gt to each ti such that (pi1
  - pi)/mri and p1/m r0

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• P-labeling Construction(Example)

Query //protein/name M1012 99 tags Ri0.01
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• Query translatortranslates an input XPath query
  into standard SQL.
• Query decomposition
• Splits the query in to a set of suffix path
  queries and records the ancestor-descendant
  relationship.
• SQL generation
• Computes the querys p-labeling and generates a
  corresponding subquery in SQL.
• SQL composition
• The subqueries are combined into a single SQL
  query based on D-labeling and the
  ancestor-descendant relationship.

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• Split algorithm
• D-elimination(query tree Q)

P//q ? p and //q
Q1
proteinDatabase
proteinEntry
Depth-first traversal
protein
reference
Split p//q into p and //q
Q2
Invokes the B-elimination if branches in Q.
Otherwise, it evaluates Q using P-labels.
refinfo
//
superfamily
year
cytochrome c
Title
2001
Join intermediate results by their D-labels
//
author
Q3
Evans, M.J.
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• B-elimination(query tree Q1)

Pq1,q2.qi/r ? p, //q1, //q2,..,//qi, //r
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B-elimination(cont..)
Q4
proteinDatabase
proteinEntry
Q7
//
Q5
reference
//
refinfo
Q8
Q9
//
year
//
Title
2001
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• Push up algorithm optimize the branch
  elimination (B-elimination).

Since p/qi and p/r are more specific than //qi
and //r,
Then split Pq1,q2,.,qi/r ? p, p/q1, p/q2,
..p/qi, p/r
proteinDatabase
Q4
proteinDatabase
proteinEntry
proteinEntry
proteinDatabase
reference
proteinEntry
refinfo
reference
Q5
proteinDatabase
refinfo
proteinDatabase
proteinEntry
year
reference
proteinEntry
2001
refinfo
protein
title
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• Unfold algorithmA further optimization of
  descendant-axis elimination(D-elimination).
• There is example as follows
• Q2/ProteinDatabase/ProteinEntry/protein//superfam
  ilycytochrome c
• Q21 /ProteinDatabase/ProteinEntry/protein/classi
  fication/
• superfamilycytochrome c ,

P//q ? p/r1/q, p/r2/q, .., p/ri/q
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Experimental Results

• Data sets
• Query sets
• Suffix path queries
• Path queries
• XPath queries
• Query Engine RDBMS or File System

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Query Execution Time
1 suffix path query 2 path query 3 XPath
query
AAuction P Protein S Shakespeare
Query time for Shakespeare, Protein and Auction
data sets
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Scalability
The performance of D-labeling, Split and Push up
for the suffix path query
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Conclusion

• P-labeling scheme is proposed to evaluate suffix
  path queries efficiently.
• BLAS combines P-labeling and D-labeling to
  evaluate XPath queries.
• BLAS is more efficient because the queries
  translated from XPath queries require
• fewer disk accesses
• fewer joins
• Experiments show the effectiveness of BLAS

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• 1J. Clark and S. DeRose. XML Path language
  (XPath), November 1999. http//www.w3.org/TR/xpat
  h.
• 13 D. DeHaan, D. Toman, M. Consens, and M. T.
  Ozsu. A
• comprehensive XQuery to SQL translation
  using dynamic interval encoding. In Proceedings
  of SIGMOD, 2001.
• 26 J.-K. Min, M.-J. Park, and C.-W. Chung.
  XPRESS A queriable compression for XML data. In
  Proceedings of SIGMOD, 2003.

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Thank you!
Question ?