SHOP

Shared Object Persistent SHOP, is an Eiffel library

Shared Object Persistent SHOP, is an Eiffel library for the Eiffel lover who wish to create distributable applications of which the various processes share a system of permanent data. Contrary to the other basic systems of directed qualified data objects, SHOP is transparent for the programmer who uses the authorities of persistent objects.

Very many applications, in particular in the field of management must work into multipost. Currently, the stations are connected between them by a local area network. In all the cases, one has the protocol of transport TCP SHOP rests on the soquets of communication TCP.

The application carried out with the support of SHOP places the root as of the its data in a store (warehouse). If the application turns in solitary mode, this one behaves like any Eiffel application. In particular, it traverses the structures of data like it usually does it with traditional structures of EiffelBase, or Gobo. A light difference appears when it is a question of modifying an element in a structure, to even see the structure it. To modify an element stored in the store, a reservation should be obtained. This is an element of the contract. Thus for example, a divided table is not extensible except if it is reserved. In solitary mode, this reservation is relatively formal, because it is not likely to fail. On the other hand, as soon as an authority of the application turns in waiter mode and others turn as a customer mode, it may be that certain reservations are refused because the desired object is already reserved. We find ourselves confronted with the traditional questions of the programming in context of competition. Except that here one should not pay attention to semaphores, questions of memory or "threads". It is only necessary to have one policy of reservation of such kind to minimize the risks of failures and deadlock. These questions are obviously truths questions of any concurrent application.

Admittedly, SHOP is very far from the conceptual level of SCOOP but it is immediately available. Moreover it is in real exploitation for some time and its reliability is enough good for performances that the traditional data bases (relational) could envy well.

To known a lithle bit more, see the user manuel here