Ajax web based diagram editor (like MS Visio)

We need to create a web pure ajax based editor (not flex or flesh, just ajax) for modeling diagrams, that have about 6 stencil with different semantic means. Every stencil, following the right semantic policy, should be linked with the other by arrowed oriented lines. We also need an automatic tool for converting the diagram into another not editable one. Finally we want to convert the previous diagram into another interactive one, automatically drawn following few standard rules. We must encapsulate that editor into REST resource, and we need a series of API to load, save and manage the content representation from DB to the diagram working in JAVA web environment. We have already made the mockup layout (see attachment) and identified all the connection and transformation rules.