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XML Indexing Structure. by XSoumia Elghani & XHanaa Talei CSC5370. Table of Content. Introduction Motivation Full Text Indexing Graphs Natix Sphinx Lore System Index Fabric. Introduction. Motivation . Web . Billion of documents. Finding a document become impossible.

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XML Indexing Structure

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Xml indexing structure l.jpg

XML Indexing Structure

by XSoumia Elghani

& XHanaa Talei

CSC5370


Table of content l.jpg

Table of Content

  • Introduction

  • Motivation

  • Full Text Indexing

  • Graphs

  • Natix

  • Sphinx

  • Lore System

  • Index Fabric


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Introduction


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Motivation

Web

Billion of documents

Finding a document become impossible

Need of efficient indexing techniques


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Full Text Indexing

A full text provides standard retrieval of all text objects.

  • B+ tree.

  • Inverted list.


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B+ Tree

  • It is the most widely used of several index structures that maintain their efficiency.

  • B+ Tree is a dynamic structure

    • Insertions and deletions leave tree height balanced

    • Almost always better than maintaining a sorted file

    • B+ tree is also based on rotation

    • Most widely used index in Data base mangement systems


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HIW?

Original:

Insert 28:


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Cont…

Insert 70:

Insert 95:


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Inverted List

They store data from the database as keys sodata content can be quickly searched on.


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Graphs

  • As we can represent data as tree, we can represent it as a graph.


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More details

Employees

Programmers

Statisticians



Leads

Workson

Consults



Projects


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Problem, solution

  • P: Many links need to be reduced

  • S: An index graph a reduced graph that will summarizes all the paths from the root.

! Important

Language Equivalent

Project

Employee.leads

Employee.workson

Programmer.employee.leads

Programmer.employee.workson

The same thing apply to p2


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Implementing an index??

  • Each node is a hash table containing one entry for each label at that node. Each index node has an extent: a list of pointers to all data nodes in the corresponding class.

    i.e: the extent of the node h4 is the list [e1, e2]

    We compute the query on the index and obtain a set of index nodes; and then we compute the union of all extents.


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Index


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Example

  • Select x from statistician.employee.(leads|consults):x

  • This query will returns the nodes h8,h9; their extents are [p5,p6,p7] and [p8] then the result of our query is the union

Results:

Simplified form of DAG

Efficient way when it can be stored in main memory


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Natix

  • An efficient, native repository for storing, retrieving and managing tree structured large objects, preferably XML documents

  • It is based on split algorithm

  • Dynamically maintains physical records of size smaller than a page which contain sets of connected tree nodes.

  • It is similar to the hybrid system , but with some extensions


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Natix Architecture

  • Record Manager: provided memory spaces divided into segments (collection of equal size pages) and each page holds one or more records.

  • Tree storage manager: operate on top of RM; it maps the tree used to model the document(topic)


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Cont..

  • Index management

  • Query engine

  • Schema manager, take care of the DTD

  • Document manager (validate the schema), make the necessary index update..

But they are not implemented yet


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Physical Model

In order to store our logical tree, there are two important ways to classify the physical node:

object content

  • Large tree


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1. Object content

  • The classification is based on the content of the node:

  • Aggregate: inner nodes of the tree; they contain their respective child nodes.

  • Literal:leaf nodes containing stream of bytes

  • Proxy: nodes which point to different records (thery are used in the representation of large trees.)


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Large Trees

Large trees are split into subtrees, and then store each subree in a single record

Scaffolding

Objects


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Second Step

Soumia


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Sphinx

  • Schema-conscious Path-Hierarchy Indexing of Xml.

  • Uses DTD to speed up the search process.

  • XML document Document Graph.

  • DTD  Schema Graph.


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Sphinx - Example


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Sphinx - Example


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Lore System

  • DBMS designed for semistructured data

  • Uses OEM graph, a label directed graph.

  • Vertices are objects

  • Each object has a unique object identifier (e.g. &19)


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Lore System


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Indexes in Lore

  • To indentify objects with specific values:

    • Value Index

    • Text Index

  • To traverse DB graph:

    • Link Index

    • Path Index


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Value Index (Vindex)

  • Implemented as B+trees

  • Takes a label ‘l’, a comparator ‘c’, and a value ‘v’

  • Returns all atomic objects having:

    • an incoming edge with the given label

    • a value satisfying the given operator and value

  • e.g. l=Pricec=‘>’ v= 15.00

    result= {&11, &15}.


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Text Index (Tindex)

  • Implemented using inverted lists.

  • Maps a given word ‘w’ and label ‘l’ to a list of atomic values with incoming edge ‘l’ that contain word ‘w’.

  • Label can be omitted for a full search.

  • Returns a list of postings (o,n) indicating that ‘w’ appears in object ‘o’ as the nth word in the value.

  • e.g. w=“Ford” l= Name

    result = {(&17,2),(&21,2)}


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Link Index (Lindex)

  • Implemented using linear hashing

  • Used to retrieve the parents of an object

  • Takes a child object ‘c’ and a label ‘l’

  • Returns all parents ‘p’ such that there is an l-labeled edge from p to c.

  • If the label is omitted, lindex returns all parents and their labels

  • Useful because there are no inverse pointers in OEM graphs.


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Path Index (Pindex)

  • Takes a given object ‘o’ (e.g. root) and a path ‘p’

  • Returns the set of objects reachable from ‘o’ following path ‘p’.

  • e.g. “select DB.Movie.Title”

    result = {&5,&9,&14}


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Index Fabric

  • Optimizes searches over semi-structured databases

  • Based on Patricia tries

  • Assigns a designator to each tag in the XML document.

  • To interpret the designators a designator dictionary is used


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Practical Algorithm to Retrieve Information Coded in Alphanumeric

Nodes are labelled with their depth

Patricia Tries


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Index Fabric – Example


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Index Fabric - Example


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Index Fabric - Example


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Conclusion

  • A number of indexing techniques

  • Different approaches

  • Under construction (e.g. Natix)

  • Still developing and improving


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References

  • Graphs: S. Abiteboul, P. Buneman, D. Suciu, “Data on the Web: from relations to semistructured data and XML”, Morgan Kuafman, 2000.

  • Natix:C.C Kanne, Guido Moerkotte. “Efficient storage of xml data“. Proc. of ICDE, California, USA, page 198, 2000.http://citeseer.nj.nec.com/kanne99efficient.html  .

  • Sphinx: L. K. Poola and J. R. Haritsa. "SphinX: Schema-conscious XML Indexing", Indian Institute of Science, 2001. http://citeseer.nj.nec.com/poola01sphinx.html


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References

  • Lore: J. McHugh, J. Widom, S. Abiteboul, Q. Luo, and A. Rajamaran. “Indexing semistructured data “. Technical report, Stanford University, Computer Science Department, 1998.http://citeseer.nj.nec.com/mchugh98indexing.html.

  • Index Fabric: B. Cooper, N. Sample, M. J. Franklin, G. R. Hjaltason, and M. Shadmon. “A fast index for semistructured data”. In Proceedings of VLDB, 2001. http://citeseer.nj.nec.com/cooper01fast.html.


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Thank You for Your Attention!


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