Purpose - To package and unpackage the persistence data from different subsystems to and from some storage medium.

The Persistence subsystem is located in org.argouml.persistence.

Currently the storage medium is a flat file (.uml - xml format) or a zipped file (.zargo - zip format)

During save the persistence subsystem requests each subsystem for its persistence data and adds that data to output it is collating.

During load the persistence subsystem unwraps the persistence data and passes these to the relevant subsystems for those subsystems to build themselves.

Edges and nodes are now saved and loaded in z order. Previously, edges were connected as they were loaded, and if the node had not already been read then this was a problem. We now load all nodes and edges (unconnected) and then connect the edges post load.

As illustrated in the figure below, the persistence subsystem depends on the kernel subsystem, and not vice versa.

Figure 5.1. Persistence subsystem dependencies.