Static fields in this class are used as part of Search initialisation
to define whether data retrieved is only for perusal or whether it can
be updated.
Key is returned by Session factory methods to create a private static key
to keep in calling classes to provide class, package or global scope session
data.
Lifetime provides typesafe definition of session lifetime, being this
session only or persist to disk to load the next time the same client
activates a session.
Split a full file name (including path) into a string for the data path used,
a String for the relative path and a third for the file name component only.