SIGCOMM 95 Middleware Workshop

Distributed Objects and Procedures

Aug. 29, 1995

John A. Zinky

jzinky@bbn.com
URL: http://www.bbn.com/dist-systems/dcntn/

BBN Systems and Technologies
Cambridge, Mass.


2) Collaborative Planning For Crisis Management Foreshadows the Complexities of Future MIS Systems

See IEEE Expert Feb 1995 "ARPA-ROME Planning Initiative"

3) Its Unique Characteristics Challenge Both Functional and System Properties of Middleware

* Not a supercomputer
* Not client/server
* Beyond workflow (not assembly line)
* Really a knowledge flow system
* Continuos Rapid Prototype-style development
* Uses multiple types of middleware to glue together legacy systems
* Must work over diverse set of resources (Kb to Gb)
* Must work under crisis workloads
* Must be deployable

4) System Issues Dominate the task of Creating Large Distributed Applications

* CORBA is a framework for exchanging information between heterogeneous distributed computing systems.,
* CORBA solves the functional problems of distributed computing, but does not mandate a specific implementations.
* Few Research issues remain , mostly engineering issues.
* CORBA does not address the systems issues involved in Distributed Computing. (Performance, Availability,Security)
* Many System-related research issue remain and CORBA is the best available architectural building block for testing out ideas.
* The main research questions are:
* "How to characterize the system requirement of applications"
* "How to characterize the system properties of a mechanism"
* "How to use the appropriate mechanism for a given situation"

5) The QuO Project Bridges the Abstraction Gap Between
Socket-Based QoS and Object-Level Programming

* QuO is general framework support for experimenting with system issues in distributed computing.
* Augment CORBA's functional Interface Description Language (IDL) with a QoS Description Language (QDL)
* Application handlers adapt to changing system resources and partial failures.
* Applications opens a connections to an object, which is has QoS regions (states) of operation.
* Application can have multiple connections to an object, each with different system properties.
* QuO can integrate mechanisms different system properties to allow an application to adapt to changing conditions.

6) Collaborative Planning Applications Have
a Spectrum of Usage Patterns and QoS Requirements

7) Many Mechanisms Give the Correct Functional Solution,
But Are Appropriate for a Small Set of System Properties

8) CORBA is a Framework for Distributing Objects and Can Support Many Different Styles of Implementations

9) Using Smart Proxy Objects Effectively Smears the Functionality of a Distributed Object Over the Network

10) Example: In-Cache Using Corba to Define the Interface

11) System issues for Longevity and Mobility

* Location: who should be responsible for finding an objects state.
* Interface Specification: What format is used to talk to an object.
* Interface Version: What happens when an interface changes.
* Performance over time: How do mechanism change as the system evolves over time.