OO System Abstractions
An application executing in a thread is abstracted as an object (e.g., COM+ object, EJB Session Bean)
Typically, lots of active objects (threads) per class
Such objects may have volatile state
- Global state (e.g., a catalog) ? each user’s request can be processed by any object
- Per-user state (e.g., a shopping cart) ? a user’s calls must all go to the same object (cf. TP Communications chapter)
EJB also offers an Entity Bean abstraction, which represents a persistent object.
- Persistence can be managed by the class (by implementing EJB-defined functions) or its container (which maps persistent data fields to the DBMS).