82 Big Data Computing
realizing a reliable and highly available storage architecture, thanks to the
multiple copies of the data stored within each cluster.
The db4o is an object-based database (Norrie etal., 2008) which provides
a support to make application objects persistent. It also supports various
forms of querying over these objects such as query expression trees and iter-
ator query methods, query-by-example mechanisms to retrieve objects. Its
advantages are the simplicity, speed, and small memory footprint.
eXist
eXist (Meier, 2003) is grounded on an open-source project to develop a native
XML database system that can be integrated into a variety of possible appli-
cations and scenarios, ranging from web-based applications to