XML in a Nutshell, 3rd Edition

Object Serialization

Like the issue of communications, the question of where and how to store the state of persistent objects has been answered in various ways over the years. In many popular object-oriented languages, such as C++ and Java, the runtime environment frequently handles object-serialization mechanics. Unfortunately, most of these technologies predate XML.

Most existing serialization methods are highly language- and architecture-specific. The serialized object is most often stored in a binary format that is not human readable. These files break easily if corrupted, and maintaining compatibility as the object’s structure changes frequently requires custom work on the part of the programmer.

The features that make XML popular as a communications protocol also make it popular as a format for serializing objects. Viewing the object’s contents, making manual modifications, and even repairing damaged files is easy. XML’s flexible nature allows the file format to expand ad infinitum while maintaining backward compatibility with older file versions. XML’s labeled hierarchies are a clean fit for nested object structures, and conversions from objects to XML and back can be reasonably transparent. Mapping arbitrary XML to object structures is a harder problem, but hardly an insurmountable one.

A number of tools serialize objects written in various environments as XML documents and can recreate the objects from the XML. Java 1.4, for example, adds an API for Long-Term Persistence ...