Native XML Databases : Why Bother

1
Native XML Databases Why Bother?
Kimbro Staken The dbXML Group http//www.dbxml.com
The dbXML Open Source Project http//www.dbxml.or
g
2
What is a Native XML Database

• a) Defines a (logical) model for an XML document
  -- as opposed to the
• data in that document -- and stores and retrieves
  documents according to
• that model. At a minimum, the model must include
  elements, attributes,
• PCDATA, and document order. Examples of such
  models are the XPath data
• model, the XML Infoset, and the models implied by
  the DOM and the events
• in SAX 1.0.
• b) Has an XML document as its fundamental unit of
  (logical) storage,
• just as a relational database has a row in a
  table as its fundamental
• unit of (logical) storage.
• c) Is not required to have any particular
  underlying physical storage
• model. For example, it can be built on a
  relational, hierarchical, or
• object-oriented database, or use a proprietary
  storage format such as
• indexed, compressed files.

3
Why Native XML Databases

• Straightforward storage of XML
• XML oriented query facilities
• Semi-structured data
• Easier construction of loosely coupled
  applications
• Tremendous flexibility and capability for change
• Not a replacement for RDBMS

4
The Problem with RDBMS and XML

• Mapping is complex and cumbersome
• With complex schemas mapping will be very slow
• Mapping will lose structural meta-data
• Documents can not be round-tripped
• Data must be highly structured
• Can't support documents with mixed content
• Limited flexibility

5
Different Types of Native XML Databases

• Custom native storage
• Software AG Tamino http//www.softwareag.com
• dbXML http//www.dbxml.org (Open Source)
• XYZFind http//www.xyzfind.com
• Built on top of object database
• Excelon http//www.exceloncorp.com
• X-Hive http//www.xhive.com
• Ozone http//www.ozone-db.org (Open Source)
• Built on top of relational database
• B-Bop Xfinity http//www.b-bop.com

6
How Do You Query

• W3C XPath
• Most common language currently used
• W3C XQuery
• Recommendation expected mid 2002
• Proprietary Languages
• Over time these will go away

7
Querying with XPath

• Simple yet powerful path based XML query language
• /root/nodecriteria 'value'
• Many products extend XPath to allow queries
  across collections of documents
• Limited in many ways
• No grouping
• No sorting
• Limited data typing

8
Querying with XQuery

• Builds on top of XPath and XML Schema data types
• Enables full data-typing
• Allows joins between XML documents
• Allows sorting and grouping
• Language is SQL like but works on trees rather
  then tables
• Currently in working draft status

9
XQuery Syntax Example
ltresultsgt FOR b IN document("http//www.bn.c
om")/bib/book, t IN b/title, a IN
b/author RETURN ltresultgt t
a lt/resultgt lt/resultsgt
10
How do you Update Data

• W3C DOM / SAX / JDOM
• XMLDB XUpdate
• Usable today
• Useful beyond just XML databases
• W3C XQuery update extensions
• Expected at some point in the future
• Will not be part of XQuery 1.0
• Experimental syntax does exist

11
XUpdate Example
ltxumodifications version"1.0"
xmlnsxu"http//www.xmldb.org/xupdate"gt
ltxuremove select"//_at_name'John'"/gt
ltxuupdate select"/addresses/address1/city"gt
Las Vegas lt/xuupdategt
lt/xumodificationsgt
12
Schemas

• Most native XML databases are schema independent
• DTDs - Just say no
• Proprietary or extended DTDs
• W3C XML Schema will likely be supported more
  widely in the future.

13
The Bad

• Products are immature
• Many standards are still in development
• Techniques are unfamiliar to people
• Not good at transaction processing
• Tool support is minimal
• Some expected database practices are still
  unsupported
• Interoperability between products is minimal

14
The Good

• Good way to store XML
• Can store document or data style XML
• Tremendous flexibility
• Applications can be loosely coupled
• Data modeling is simple and flexible
• Complement RDBMS with XML mapping solutions
• Performance can be very good

15
The End
Questions?