Querying XML Database Using Relational Database System

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Querying XML DatabaseUsingRelational Database
System

• Rucha Patel
• MS CS (Spring 2008)
• Advanced Database Systems CSc 8712
• Instructor Dr. Yingshu Li

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Outline of Presentation

1. Background Information regarding XML
2. Storing XML documents in relational DB system
3. Querying Manipulating XML data
4. XML Data Models for Query Processing
5. XML Labeling Schemes
6. Structural Joins
7. General Technique for Querying XML Documents
   using Relational DB System
8. XQL ( XML Query Language )
9. Conclusion

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Background Information - XML

• Evolved from a document markup language
• For exchange of structured and semi-structured
  data
• For self-describing data -gt between heterogeneous
  data sources
• XML Data Management Systems
• Specialized system only for XML documents
• General System manage XML along with other data
  formats.

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Background Information XML ( Contd )

• 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
• 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
• 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
• Distributes XML information across one/more
  columns of tables preserving both data values
  structural relationships.
• For XML schema gt tables
• levels of elements.
• at each level different tables for elements in
  hierarchy
• Schema Based Shredding
• Not efficient with
• sparse element - with varying contents
• Mixed contents text child elements
• Fails to preserve
• Document ordering
• Processing instructions of XML documents

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Storing XML Documents in RDB System ( Contd )

• 3) XML Publishing
• to reconstructs XML documents from relational
  tables,
• Systems usually provides inverse information
  called XML Publishing
• 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

• XML Storage facility -gt interface to access and
  manipulate stored data.
• XPath better navigation within documents but,
• can not transform structures
• Can not construct new elements
• XSLT transformation Construction But,
• Recursive template-driven nature unsuitable for
  optimization
• XQuery complete set of query facilities.

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Querying Manipulating XML Data ( Contd )

• XML Data Model
• XML documents as ordered, labeled, finite,
  unranked trees.
• Relative order of nodes order of siblings
• Region encoding labeling scheme
• lt doc, start, end, level gt
• Doc to which document, node belongs to
• Start end position of element in a document
• Level level of a node in a tree
• X is an ancestor of y, if and only if
• x.start lt y.start and x.end gt y.end

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Querying Manipulating XML Data ( Contd )

• XML Labeling Schemes
• To evaluate queries in XPath, XSLT XQuery,
• Maintain results throughout the evaluation in
  document order
• Restricts choice of query plans
• Impossible if query requires data to be resorted
  along different axis at some point.
• Sort Operator handled at appropriate times
• 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 )

• Storing XML in RDBMS
• Labeling Scheme edge shredding form a single
  relation for storing XML Doc
• Edge relation
• Global Encoding Scheme
• Edge(id, parent-id, end, path-id, value)
• Local Encoding Scheme
• 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

• To store and query an XML Doc
• 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...

• To use the same query processor for relational
  schema generation and converting queries,
• Along with shredding, Reconstruction XML View is
  created over relational tables
• Virtually reconstructs the
• Stored XML Doc lt- 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...

• For Relational Schema Generation, a program that
• Generated desired relational schema
• Produce XML Shredder object
• Create reconstruction XML view
• Either for,
• Shared relational schema
• Edge relational schema

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Contd...

• Shared Relational Schema
• Steps to generate relational schema
• 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,
• -node, - is a set values cant 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 )

• Structured Queries relational / OO DB
• Unstructured Queries Documents
• Semi-structured Queries XML Documents
• Features like,
• Allows, user to combine information from multiple
  sources
• Uses links as a part of a query
• Search based on text containtment
• Eg ) Doc1 recommended books
• Doc 2 Books Prices
• Doc 3 Reviews of Books
• Then, a query -gt list recommended books, prices
  and reviews.

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XQL ( XML Query Language ) Contd

• 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

• Basic Concepts of XQL
• Simple string element name
• Eg. table
• / child operator indicates hierarchy
• Eg. Front/author
• front/author'Theodore Seuss Geisel'
• front/author/address/_at_type'email'
• front//address
• //address
• front/author/address_at_type'email'
• front/author'Theodore Seuss Geisel'_at_gender'male
  ' and shoesize'9EEEE'
• section1,3 to 5, 8, -1
• section_at_level'3'1 to 2

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XQL ( XML Query Language ) Contd

• Example Queries

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XQL ( XML Query Language ) Contd

• Example Queries

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XQL ( XML Query Language ) Contd

• 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

• Join
• Combine information from multiple sources to
  create one unifies view.
• Queries can be written like,

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Conclusion

• 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.
• Structured Materialized Views for XML Queries
  by Andrei Arion, Veronique Benzaken Ioana
  Manolescu.

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Thank You.

• Any Questions ???

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