Download Querying XML Database Using Relational Database System

Querying XML Database
Using
Relational Database System
Rucha Patel
MS CS (Spring 2008)
Advanced Database Systems CSc 8712
Instructor : Dr. Yingshu Li
5/22/2017
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Outline of Presentation
Background Information regarding XML
Storing XML documents in relational DB system
Querying & Manipulating XML data
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2.
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XML Data Models for Query Processing
XML Labeling Schemes
Structural Joins
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2.
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6.
General Technique for Querying XML Documents
using Relational DB System
XQL ( XML Query Language )
Conclusion
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Background Information XML
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Evolved from a document markup language
 For exchange of structured and semi-structured
data
 For self-describing data -> between
heterogeneous data sources
 XML Data Management Systems
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Specialized system – only for XML documents
General System – manage XML along with other data
formats.
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Background Information –
XML ( Contd… )
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XML is a recommendation of W3C
XML Schema – Type System for XML
XPath – A language for navigating within XML
documents
XSLT – an XML transformation language
XQuery – a general purpose XML query
language
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Based on XML Schema types
Includes XPath as a subset.
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Storing XML Documents in
RDB System
1 ) Simplest one is to use Long Character String
data type like, CLOB in SQL
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Will store entire document as a character string
Textual Fidelity
Fails to take advantage of structural information
available in XML markup
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Storing XML Documents in
RDB System ( Contd… )
2 ) Shredding
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Distributes XML information across one/more columns of tables
preserving both data values & structural relationships.
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For XML schema => tables
levels of elements….
at each level – different tables for elements in hierarchy
Schema Based Shredding
Not efficient with
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sparse element - with varying contents
Mixed contents – text + child elements
Fails to preserve
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Document ordering
Processing instructions of XML documents
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Storing XML Documents in
RDB System ( Contd… )
3) XML Publishing
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to reconstructs XML documents from relational tables,
Systems usually provides inverse information called “XML
Publishing”
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Such Systems with shredding + XML publishing are
said to provide Relational Fidelity
As authoritative form of data is relational, not XML.
4) Native XML with XML Fidelity.
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Querying & Manipulating
XML Data
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XML Storage facility -> interface to access and
manipulate stored data.
 XPath – better navigation within documents but,
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XSLT – transformation + Construction But,
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can not transform structures
Can not construct new elements
Recursive template-driven nature – unsuitable for
optimization
XQuery – complete set of query facilities.
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Querying & Manipulating
XML Data ( Contd… )
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XML Data Model
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XML documents as ordered, labeled, finite, unranked
trees.
Relative order of nodes – order of siblings
Region encoding labeling scheme
< doc, start, end, level >
• Doc – to which document, node belongs to
• Start & end – position of element in a document
• Level – level of a node in a tree
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X is an ancestor of y, if and only if
• x.start < y.start and x.end > y.end
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Querying & Manipulating
XML Data ( Contd… )
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XML Labeling Schemes
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To evaluate queries in XPath, XSLT & XQuery,
1. Maintain results throughout the evaluation in document
order
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Restricts choice of query plans
Impossible if query requires data to be resorted along different
axis at some point.
2. Sort Operator – handled at appropriate times
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Assign each node a label – denoting relative order
Like, region encoding scheme
• Ancestor-descent problem
Variable size labeling scheme
• Do not need to relabel a node on update.
• Difficult to allocate fixed portion of each record for label.
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Querying & Manipulating
XML Data ( Contd… )
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Storing XML in RDBMS
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Labeling Scheme + edge shredding = form a single
relation for storing XML Doc
Edge relation
1. Global Encoding Scheme
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Edge(id, parent-id, end, path-id, value)
2. Local Encoding Scheme
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Edge(id, parent-id, sIndex, path-id, value)
sIndex – position of a node among siblings
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General Technique for
Querying XML Doc in RDBMS
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To store and query an XML Doc
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Relational Schema Generation – table creation
Shredding – storing XML Doc
Converting queries over stored XML into SQL
queries over created tables
Relational schema generation – requires its
own query processor to convert the queries
But, the same query processor can be used..
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Contd...
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To use the same query processor for relational
schema generation and converting queries,
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Along with shredding, Reconstruction XML View is
created over relational tables
Virtually reconstructs the
Stored XML Doc <- shredded rows.
Just like the normal view over the Stored XML Doc.
Queries on Stored XML = Queries over
Reconstruction XML View
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Contd...
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Contd...
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For Relational Schema Generation, a program
that
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Generated desired relational schema
Produce XML Shredder object
Create reconstruction XML view
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Either for,
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Shared relational schema
Edge relational schema
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Contd...
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Shared Relational Schema
Steps to generate relational schema
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Create a DTD Graph node ( XML Element,
Attribute, Operator)
Create a relation for root element in graph
All children of element are represented in same
relation of element EXCEPT,
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*-node, - is a ‘set’ values + can’t captured by relational
expressions
So, create separate relation for these nodes.
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Contd...
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Contd...
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Contd...
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XQL ( XML Query Language )
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Structured Queries – relational / OO DB
Unstructured Queries – Documents
Semi-structured Queries – XML Documents
Features like,
Allows, user to combine information from multiple sources
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Uses links as a part of a query
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Search based on text containtment
Eg ) Doc1 – recommended books
Doc 2 – Books + Prices
Doc 3 – Reviews of Books
Then, a query -> list recommended books, prices and reviews.
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XQL ( XML Query Language )
Contd…
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Difference between SQL & XQL Query
SQL
XQL
The database is a set of tables.
The database is a set of one or more
XML documents.
uses the structure of tables as a basic
model.
uses the structure of XML documents
as a basic model.
The FROM clause determines the
tables which are examined by the
query.
A query is given a list of input nodes
from one or more documents.
The result of a query is a table
containing a set of rows; this table may
serve as the basis for further queries.
The result of a query is a list of XML
document nodes, which may serve as
the basis for further queries.
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XQL ( XML Query Language )
Contd…
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Basic Concepts of XQL
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Simple string – element name
• Eg. table
‘/’ – child operator – indicates hierarchy
• Eg. Front/author
‘front/author='Theodore Seuss Geisel'
front/author/address/@type='email'
front//address
//address
front/author/address[@type='email']
front/author='Theodore Seuss Geisel'[@gender='male' and
shoesize='9EEEE']
section[1,3 to 5, 8, -1]
section[@level='3'][1 to 2]
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XQL ( XML Query Language )
Contd…
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Example Queries
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XQL ( XML Query Language )
Contd…
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Example Queries
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XQL ( XML Query Language )
Contd…
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Grouping of results
Query –
lists the products on invoices might want to group products by invoice, placing each
group of products within an invoice tag.
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XQL ( XML Query Language )
Contd…
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Join
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Combine information from multiple sources to create one unifies
view.
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Queries can be written like,
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Conclusion
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XML Documents can be stored efficiently in a relational
database system using number of approaches.
General Technique for storing and querying XML
Document using RDBMS eliminated need of separate
query processors for XML query translation.
Using General Technique Reconstruction XML View can
be generated for both shared and edge based relational
schema.
Stored XML Document can be queried effectively
through the use of XQuery, XPath, XSLT or XQL.
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References
“XML and Relational Database Management Systems :
the inside Story” by Michael Rys, Don Chamberlin, &
Daniela Florescu.
 “A General Technique for Querying XML Documents
using a Relational Database System” by Jayavel
Shanmugasundaram, Rajasekar Krishnamurthy, Igor
Tatarinov.
 “Querying and Maintaining Ordered XML Data Using
Relational Databases” by Willium SHui, Franky Lam,
Damien Fisher & Raymond Wong.
 “Querying Structured Text in an XML Database” by
Shurung Al-Khalifa, Cong Yu, H.V. Jagdish.
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 “Structured Materialized Views for XML Queries” by
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Thank You.
Any
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Questions ???
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