Here is what the specs mention on this subject P364
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The
EJB specification does not prescribe how the Container should manage the execution of a method with an unspecified transaction context�the transaction semantics are left to the Container implementation.
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so to answer your question accessing other beans / resource managers is left solely to the implementation of the container. The specs give some examples of possible solutions .......
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->The Container may execute the method and access the underlying resource managers without a transaction context.
->The Container may treat each call of an instance to a resource manager as a single transaction (e.g. the Container may set the auto-commit option on a
JDBC connection).
->The Container may merge multiple calls of an instance to a resource manager into a single transaction.
->The Container may merge multiple calls of an instance to multiple resource managers into a single transaction.
->If an instance invokes methods on other enterprise beans, and the invoked methods are also designated to run with an unspecified transaction context, the Container may merge the resource manager calls from the multiple instances into a single transaction.
->Any combination of the above.
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I hope this helps !!