[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message]

Re: XML-enabled databases, XQuery APIs


xml enabled sql database
> I don't understand this nearly well enough.   In a
> relational database, what are the characteristics
> of an "XML type"?


In the mid-1980s, SQL databases stored tabular data and the SQL standard
included alphanumeric types (numbers and characters).

Fast forward ten years and databases had to support more complex types.
Applications required geo-spatial data, multidimensional data, time series,
images, audio, video and text. Object-relational technology emerged and SQL
platforms began supporting user-defined types, user-defined functions and
content-based queries.

A classic example was the sunset query at the California Department of Water
Resources (DWR). By 1995, DWR had a half-million 35mm slides. It classified them
for an SQL database using keywords and text descriptions. That classification
and indexing scheme was inadequate. Clients requested photos based on content,
such as a search for a reservoir with a low water level. To provide
content-based SQL queries, DWR digitized the images in Photo-CD format and put
them in the database. That enabled them to run content-based SQL queries such as
finding images of sunsets (based on detecting orange at the top of the image).

Fast forward to 2003 and now the SQL:2003 standard includes nested collections,
multisets and an XMLType.

Implementation of the standard is a bit more work than simply updating the
parser. Supporting a data type means the SQL DBMS provides a data definition
syntax, type checking, constraints, rules and access methods. It knows how to
store, index, and optimize queries involving that type.

The optimizer determines the best access plan for a query and it uses indexes
for performance. For queries with alphanumeric types, a DBMS can use b-tree
indexes and b-tree based data access. For complex types, the SQL platform must
use different access methods and indexing techniques such as r-trees, quadtrees,
KDB-trees and so on.

So an SQL column of XMLType is a hierarchically-nested collection of elements.
There's a structure to the data, order must be preserved, and it's understood by
SQL DDL and DML.


======== Ken North ===========
www.WebServicesSummit.com
www.SQLSummit.com
www.GridSummit.com


PURCHASE STYLUS STUDIO ONLINE TODAY!

Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced!

Buy Stylus Studio Now

Download The World's Best XML IDE!

Accelerate XML development with our award-winning XML IDE - Download a free trial today!

Don't miss another message! Subscribe to this list today.
Email
First Name
Last Name
Company
Subscribe in XML format
RSS 2.0
Atom 0.3
 

Stylus Studio has published XML-DEV in RSS and ATOM formats, enabling users to easily subcribe to the list from their preferred news reader application.


Stylus Studio Sponsored Links are added links designed to provide related and additional information to the visitors of this website. they were not included by the author in the initial post. To view the content without the Sponsor Links please click here.

Site Map | Privacy Policy | Terms of Use | Trademarks
Free Stylus Studio XML Training:
W3C Member
Stylus Studio® and DataDirect XQuery ™are products from DataDirect Technologies, is a registered trademark of Progress Software Corporation, in the U.S. and other countries. © 2004-2013 All Rights Reserved.