Siena 介绍
Siena 是一个 Java 的简易数据持久层框架，支持 Google App Engine 数据存储。
Siena is a single API with many implementations. You can use siena with
relational databases, with the Google App Engine’s datastore or with Amazon’s
SimpleDB. There is also an implementation called siena-remote very useful if
you want to use the Google App Engine’s datastore remotely. Other
implmenetations are planned such as: HBase, DBSLayer,…