The Xtu top level design

The building blocks of Xtu are given by the xUML formalism, developed by Sally Shlaer and Stephen Mellor. Here, it's out of the scope to explain the Whys and Hows of the formalism. Interested readers are refered to the links page for more information.

Starting with the (side) view of the Plattform independent vs. Plattform specific parts:

PIM vs PSM view.

Domains, Bridges, Classes, FSMs, Events, Signals and Operations are all represented as PIM entities. Bridges have a PSM conterpart that allows domains to be deployed in single or multi-threaded environments.

Xtu has no yet any support for formal Relations or relational algebra. Information models have to be implemented by hand using pointers, references, arrays, lists, hash tables, iterators or whatever construct/library (e.g. STL or Qt) deemed usefull in the specific case. Consequently, all Relations are platform specific. In the future, this shortcoming will hopefully be addressed. Execution context is directly bound to the deployment platform and therefore platform specific.

Looking at the PIM vs. PSM-view from the top shows how the Domains, Bridges and Execution contexts are related.

Domains, Bridges & Execution contexts.

Domains are connected to each other using bridges (as defined by the xUML formalism). All bridges send and receive asynchronous signals and/or synchronous operations. The underlaying bridge type provide varios possibilities for deployment. Domains connected using single threaded bridges (SingleTB_* in the figure above) are deployed in the same execution context and thus executed by the same thread or process. Domains connected using multi-threade bridges (MultiTB_*) are deployed in separate execution contexts and execute in parallell on two different threads. In the future, it is expected to also have netcentric brige types for distributed deployment.

This way of using bridges to separate execution contexts, provides flexible deployment opportunities. Domains are singletons in relation to their execution context. Thus, any given domain may only be deployed in a single execution context.

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