Introduction

Distributed object-oriented systems are built using collaborating objects on a distributed platform. These distributed objects collaborate by passing messages. In some cases, applications may require to change their message control policies dynamically. For example, an application might need to check message contents for validity or against security concerns. In such cases, message control cannot be abstracted out without breaking its transparency. In applications like these, interceptors[8] or filtering models models such as Composition Filters[1], Filter Objects[6] and Encapsulators[9] achieve separation between message processing and message control. In the filter object model, messages sent to the destination objects can be intercepted by first class filter objects. While filter objects intercept messages, the calling semantics of the source object do not change. This behavior of filter objects can be employed to change the system behavior by transparently intercepting calls and controlling or modifying the invocation requests coming from clients. In this paper, an implementation of a filter object framework for MICO[12], an open source implementation of CORBA[12] is described.

Figure 1: Direct delivery model