I have heard of the pureXML feature of DB2 9 and want to switch to DB2 9. Can someone tell more about DB2 9 and PureXML?

DB2 9 is a hybrid database system. It can have both relational data and native XML data in the same database. DB2 9 introduces an XML data type. The relational data is stored in tabular structures and the XML data is stored in tree structure. The structure enables XML data to be stored in its hierarchical form within columns of a table. Because data is stored in its native form, both types of data can benefit from the performance. On top of both tabular structures and tree structures, there is one hybrid database engine that processes both types of data. There are two different parsers to process SQL and XQuery. A single compiler is used for both languages. DB2 9’s compiler and optimizer can handle both languages. An application can use the combinations of SQL and XQuery to access relational and XML data in the hybrid database. DB2 9 treats XML as a native data type. It has pureXML storage, meaning that XML data is stored in XML form, which is a hierarchical structure.

I have some data that I want to store in the DB2 9. Should I store this data as XML schema or relational schema?

This depends on the data you want to store in the database. The main difference between relational schema and XML schema is that relational schema describes data as strongly structured and typed. XML schema describes data as loosely structured and typed. XML schema describes data order, but relational schema does not.
In general, data that has the following properties should be stored in XML:
The data is better described in hierarchal format.
The schema is constantly changing and evolving.
Many attributes of the data are empty or unknown.
You can check http://www.ibm.com/developerworks/xm...GX06&S_CMP=EDU for advice on creating XML.

The data which I want to store in the database contains small amount of data, but have a highly complex structure. Should I store this in XML data type?

You should store such data in XML. If you store such data in relational tables, you will have complicated relational schemas, which means you require many tables. Managing these tables can have overhead. The SQL query to access such data requires joining many tables. If you have to process this data together with other data, the SQL query will be even more complicated.

Is there any way to validate the XML data against a XML schema before inserting into the database?

DB2 9 supports validating XML documents with XML schema at insert or import time. The XML schemas have to be registered in XML Schema Repository (XSR) before it can be used for validation. The XML document in the same XML type column can be validated by a different XML schema of your choice in the insert/import time. You can also choose not to validate the XML. In general, there are three choices:
Validate on the server.
Validate within an application.
Do not validate.
XML validation enables you to create complex rules that define acceptable data. You can check http://www.ibm.com/developerworks/xm...ary/x-tipxsslt to use the XML Schema Standard Type Library to simplify the process of requiring formatted data such as e-mail addresses and telephone numbers.

You can check http://www.ibm.com/developerworks/xm...ary/x-tipxsslt to use the XML Schema Standard Type Library to simplify the process of requiring formatted data such as e-mail addresses and telephone numbers.

You can check http://www.ibm.com/developerworks/xm...ary/x-tipxsslt to use the XML Schema Standard Type Library to simplify the process of requiring formatted data such as e-mail addresses and telephone numbers.