1. By Daniela Floresu Donald Kossmann
A Performance Evaluation of Alternative Mapping Schemes for Storing XML Data in a Relational Database By
Daniela Floresu
Donald Kossmann
Presented by:
Intakhab Mehboob Khan

2. Table of Contents Introduction
Approaches to Store Semi-Structured Data
Data Model for Semi-Structured Data
Query Language and XML-QL
Storing XML Data in Relational Database
Mapping Attributes
Mapping Values
Evaluating the Mapping Schemes
Conclusion

3. Introduction August 3, 1999 How XML data can be stored and Queried
Presented alternative Mapping Schemes to Store XML data
Performance experiments that analyze the tradeoffs of the schemes

4. Approaches to Store Semi-Structured Data
Special Purpose Database System
Examples are Lore, Rufus and Strudel
Store and retrieve xml data, using specially designed structures and indices
Object Oriented Database
Example is O2 or Objectsore
Rich data modeling capabilities of OODMS are exploited
Standard Relational Database System
Data is mapped in tables of a relational schema

5. Data Model for Semi-Structured Data
Characteristics of Semi-Structured Data
Schema is not given in advance, may be implicit
Schema is relatively large and may be changing frequently
Schema is descriptive rather than perspective
Data is not strongly typed
Simple graph data model similar to OEM model

6. Data Model for Semi-Structured Data

7. Query Language and XML-QL
All query languages for semi-structure are based on labeled graph
Features of Semi-Structure query language
regular path expression
ability to query the schema
In addition, XML-QL restructuring mechanism

8. Storing XML Data in Relational Database [Mapping Attributes]
Edge Approach
Store all attributes in single table
Edge(source, ordinal, name, flag, target)
Indexing, Forward and backward traversals
Variant of Edge approach is: Store attributes name in separate table

9. Storing XML Data in Relational Database [Mapping Attributes]
Attribute Approach
All the attributes with the same name in one table
Resembles to binary storage scheme proposed to stir semi-structure data
Aname(source, ordinal, flag, target)
Indexing

10. Storing XML Data in Relational Database [Mapping Attributes]
Universal Table
Single Universal table to store all attributes of XML document
Universal(source, ordinaln1, flagn1, targetn1,…..)

11. Storing XML Data in Relational Database [Mapping Attributes]
Normalized Universal Table
Multi-valued attributes are stored in separate Overflow tables
UnivNorm(source, ordinaln1, flagn1, targetn1,…..)
Overflow(source, ordinal, flag, target),….

12. Storing XML Data in Relational Database [Mapping Values]
Storing values in separate table
Value table storing all integers, dates, and all strings
Vtype(vid, value)

13. Storing XML Data in Relational Database [Mapping Values]
Storing values together with attributes
Column for each data type: Inlining
No flag is needed
For indexing, on every value columns separately in addition to source and target

14. Evaluating the Mapping Schemes
Plan of Attack
Size of Relational Database for each mapping scheme
The time to bulkload the relational database given an XML document
The time to reconstruct the XML document from the relational data
The time to execute different classes of XML queries
The time to execute different kinds of update functions

15. Evaluating the Mapping Schemes
Experimental Platform
Commercial relational database system, installed on Sun Sparc Station 20 with
Two 75 MHZ processors
128MB of main memory & a disk that stores the database and intermediate results of query processing
Machine runs on Solaris 2.6, with limited size of main memory buffer to 6.4MB
Calls to relational database from the Java programs are implemented with JDBC

16. Evaluating the Mapping Schemes
Benchmark Specification
Benchmark Database

17. Evaluating the Mapping Schemes
Benchmark Specification
Benchmark Queries

18. Evaluating the Mapping Schemes
Benchmark Specification
Update Functions

19. Evaluating the Mapping Schemes
Benchmark Specification
Database Size

20. Evaluating the Mapping Schemes
Benchmark Specification
Bulkloading Times

21. Evaluating the Mapping Schemes
Benchmark Specification
Reconstructing the XML Document

22. Evaluating the Mapping Schemes
Benchmark Specification
Running Times of the Queries

23. Evaluating the Mapping Schemes
Benchmark Specification
Running Times of the Updates Functions

24. Conclusion Relational database has following advantages Disadvantages
Mature and Scale very well
Traditional and Semi-structured data can co-exist in relational database
RDBMS are capable of performing more complex XML queries on large database
Disadvantages
Very expensive to reconstruct the original XML data from relational database
Components such as authorization and concurrency control need to be implemented outside RDBMS

25. Conclusion (Cont’d) Alternative mapping schemes results shows:
Attribute tables for every attribute name that occurs in an XML document and inlining of values into these Attributes tables is the best approach