Building a Truly Distributed Constraint Solver with JADE

Real life problems such as scheduling meeting between people at different locations can be modelled as distributed Constraint Satisfaction Problems (CSPs). Suitable and satisfactory solutions can then be found using constraint satisfaction algorithms which can be exhaustive (backtracking) or otherwise (local search). However, most research in this area tested their algorithms by simulation on a single PC with a single program entry point. The main contribution of our work is the design and implementation of a truly distributed constraint solver based on a local search algorithm using Java Agent DEvelopment framework (JADE) to enable communication between agents on different machines. Particularly, we discuss design and implementation issues related to truly distributed constraint solver which might not be critical when simulated on a single machine. Evaluation results indicate that our truly distributed constraint solver works well within the observed limitations when tested with various distributed CSPs. Our application can also incorporate any constraint solving algorithm with little modifications.Comment: 7 page

OCI-Based Group Communication Support in CORBA

Group communication is a useful mechanism guaranteeing consistency among replicated objects. The existing approaches do not allow transparent plug-in of group communication protocols into CORBA. They either require modification of CORBA or OS, or provide no room for incorporating group communication transport protocols into CORBA. We thus propose a generic group communication framework that allows transparent plug-in of various group communication protocols with no modification of existing CORBA. We extend the open communications interface (OCI) to support interoperability, reusability of existing group communication, and independency on ORB and OS. We also define the group communication inter-ORB protocol (GCIOP) as a group communication instantiation of the general inter-ORB protocol (GIOP) that encapsulates underlying group communication protocols. The proposed scheme can be exploited for fault-tolerant CORBA (FT CORBA)

OCI-Based Group Communication Support in CORBA

Group communication is a useful mechanism guaranteeing consistency among replicated objects. The existing approaches do not allow transparent plug-in of group communication protocols into CORBA. They either require modification of CORBA or OS, or provide no room for incorporating group communication transport protocols into CORBA. We thus propose a generic group communication framework that allows transparent plug-in of various group communication protocols with no modification of existing CORBA. We extend the open communications interface (OCI) to support interoperability, reusability of existing group communication, and independency on ORB and OS. We also define the group communication inter-ORB protocol (GCIOP) as a group communication instantiation of the general inter-ORB protocol (GIOP) that encapsulates underlying group communication protocols. The proposed scheme can be exploited for fault-tolerant CORBA (FT CORBA)

Making Consensus Practical

This paper presents the abstraction of lazy consensus and argues for its use as an effective component for building distributed agreement protocols in practical asynchronous systems where processes and links can crash and recover. Lazy consensus looks like consensus, is equivalent to consensus, but is not consensus. The specification of lazy consensus has an on-demand and a re-entrant flavors that makes its use very efficient, especially in terms of forced logs, which are known to be major sources of overhead in distributed systems. We illustrate the use of lazy consensus as a building block to develop efficient atomic broadcast and atomic commitment protocols: two central abstractions in our DACE middleware environment

Open Consensus

This paper presents the abstraction of open consensus and argues for its use as an effective component for building reliable agreement protocols in practical asynchronous systems where processes and links can crash and recover. The specification of open consensus has a decoupled, on-demand and re-entrant flavour that make its use very efficient, especially in terms of forced logs, which are known to be major sources of overhead in distributed systems. We illustrate the use of open consensus as a basic building block to develop a modular, yet efficient, total order broadcast protocol. Finally, we describe our Java implementation of our open consensus abstraction and we convey our efficiency claims through some practical performance measures

Programming with Object Groups in CORBA

Our Object Group Service extends CORBA with the ability to gather several objects inside a group and to transparently handle the group membership and the consistent invocations of the group members. We describe the programming model of the Object Group Service through four different distributed application examples. Each of these examples illustrates a particular area where object group semantics are well adapted. Keywords: CORBA, Distributed Objects, Object Groups, Reliability IEEE Concurrency Special Theme Track on Object-Oriented Systems 1 Introduction Most of object-based distributed architectures heavily rely on remote method invocation as a basic abstraction for inter-object communication. The advantage of this abstraction is that it simplifies distributed programming by making communication with a remote object look like communication with a local object. Its limitation, however, is that it can only be employed for two-ways communication between a client object and a server ..