In this tutorial, I will focus on the roles, types, and issues of middleware. I will give a short overview of the software problems that middleware addresses and (mostly) solves. I will do a survey of the different kinds of middleware and their applicability to diverse problem domains. I will spend somewhat longer discussing, with examples, CORBA, RMI, and Jini, in particular pointing out relative strengths and weaknesses. Finally, I will discuss some of the major and outstanding research issues, especially those that a PODC audience might find stimulating, and suggest where and how solutions might be found.

This paper describes the design and implementation of a fault-tolerant CORBA naming service-CosNaming FT. Every CORBA object is accessed through its Interoperable Object Reference (IOR), which is registered with the CORBA name service. The name service therefore is a critical gateway to all objects in a distributed system; to avoid having a single point of failure, the name service should be made fault-tolerant. CosNamingFT uses the GroupPac package, a CORBA-compliant suite of protocols, to replicate the name server. GroupPac services are built from Common Object Services that function as building blocks to implement fault-tolerant applications. This paper aims to demonstrate the usefulness of some of these object services and to demonstrate the importance of open solutions issues in replicating distributed objects.

No abstract available.