This is the deployment of Content Hosting Service and Resources in all versions of Sakai prior to 2.5.
In 2.5 with Post-2.5 Components, it will be possible to run with Legacy CHS and to use tools developed on JCR. The content of the tools can be exposed bi-directionally to read-write using the JCRContentHostingHandler. Either a site administrator or the tool itself can perform the mount operation.
This means that content can be uploaded from either the new tool or resources into the space managed by JCRService and content in the new tool can be read, updated and used in legacy tools. However the new tool will not be able to access all content stored under the legacy content hosting service.
For content migration, the exposed Content Hosting Service API is replaced with a Multiplexer (CHS MUX), that controls which CHS implementation is active. Initially the Legacy CHS will be active. A Content Migration Service will build a list of content items to migrate, and then migrate those items into the JCR Content service. As content is modified the queue will be added to, resulting in some rework of existing items. When the queue has reached a steady state. An operator will schedule downtime and the CHS-MUX will be switched over. As the app servers come up, the remaining small number of items on the queue will be migrated over and all activity will take place via the CHS JCR implementation. At that point the deployment can move onto full JCR Content Storage.
Once the migration is complete, the DB Content Hosting Service can be removed, and all operations can be performed against the JCR Service. This does not reduce the code base supported by Sakai, but it does put us in a position to move forwards and gain significant functionality with minimal effort or risk.
Ultimately we will reimplement the Resources tool with input from Fluid and remove all of the legacy content hosting codebase. This reimplementation may break up the Resources tool into other, new tools e.g. a File Manager and a Content Presentation Tool. The Resources Tool in the diagram illustrates that future Resources Tool features will be supported by JCR-provided content and illustrates the third connection option for a new tool - direct to JCRService. Other services and tools (file helpers, OSP use of resources, etc.) will be replaced with off-the-shelf open source components (eg Jackrabbit WebDav) or rebound to one of the 3 JCR-based services.
