XML Serialization

Classic Defintion:
The reversible process of encoding a data structure as a sequence of bytes

Marshall & Unmarshall:
Marshalling is the process of generating XML document from the instance of Java Class(or any other language in context) and as unmarshalling is interpreting java object from xml document.

Usage:
Wherever xml <--> java occurs heavily. For example, SOAP clients or any other XML intensive processing in java

Frameworks:
Breeze XML Binder, a tool produced by Breeze Factor
http://www.breezefactor.com/.
JAXB Reference Implementation, created by SUN
http://java.sun.com/xml/jaxb/.
Castor:an open source project under ExoLab
http://www.castor.org/spring-xml-intro.html
http://www.ibm.com/developerworks/xml/library/x-xjavacastor2/
XML Beans: Apache Open Source
http://www.onjava.com/pub/a/onjava/2004/07/28/XMLBeans.html

Comparision:
http://www.xml.com/pub/a/2003/09/03/binding.html
http://dev2dev.bea.com/pub/a/2004/05/ryan_xml.html


Known Issues:

1. The language of XML Schema is much richer than the object model of Java,
2. Not all XML names can be turned into Java identifiers, xsd:enumeration declarations cannot be nicely mapped into Java types (even since Java 5),
3. Some Java types are by nature explicitly unportable.
4. XML is a hierarchical data structure, and can only describe trees or lists of data, while Java classes almost invariably refer to other objects, oftencreating cyclic graphs of references.
5. Each node in an XML message can have a separate namespace, which cannot be expressed in Java.

O/X Mapping:
The upcoming improvements are to provide a way to map Object to XML document to overcome most of the known issues