Operating Systems Lecture Notes

18 April 2012 • Middleware

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Outline

• Middleware
• Frameworks
• Transaction processing example
• Systems engineering.
• Trends

Introduction

• Connection hierarchy: hardware, network subsystem, OSs, applications.
• Spread out and unify applications as an objective.
• The main problems are syntactic (heterogeneity) and semantic (APIs).
• The standard solutions apply: Hide the syntax, define (make standard) the APIs.

Middleware

• Middleware is the 8th level in the ISO stack.
• A middleware API abstracts away heterogeneity, leaving a uniform and independent syntax.
• Middleware hoists OS functions and spreads them over the network.
• The OS and application are unified via the middleware API.

Middleware Structure

• Middleware is a layer between an OS and host-resident systems.
• Formal organization around APIs and protocols, but not around implementations.
• Several over-all middleware architectures.
  • Client-server, message queue (messages over middleware, MOM), publish-subscribe.

Heterogeneity

• Abstracting away heterogeneity requires several properties:
  • Portability to reduce implementation, and other, costs.
  • Transparent APIs so the application fits the service, not the middleware.
• There's an open boundary between middleware and operating systems.
  • Middleware → OS for performance.
  • OS → Middleware for distribution.

Example Services

• Example middleware services include

  Presentation management		Google chart service
  Computation		Google translate
  Information Management		Delicio.us
  Communication		E-mail
  Control		Grid computing
  System management		ICMP

General Issues

• Identify and factor common functions into middleware.
• Transparency vs technological change.
• Managing heterogeneity tends toward complexity and expense.
• Exploiting middleware can also be a complex moving target.

Frameworks

• A framework is an application skeleton to access middleware services.
• The framework API further abstracts the middleware API.
  • And shapes it for a particular application family.
  • And smooths over differences in middleware implementations (wheel of reincarnation).

Framework Functions

• A framework for visualizing distributed-application performance.
• Manage implicit context to simplify middleware interaction.
• Simplify middleware APIs in general.
• Implement missing or mis-configured middleware.

Framework Tools

• Frameworks frequently include development and management tools.
• Tools can be integrated via data, control, or presentation.
• Data sharing is the most powerful, and the most complex integration.
• Control sharing is useful for application building.
• Presentation sharing at the user interface.
• Control and presentation integration over data sharing.

Transaction Processing

• A transaction is an uninterrupted interaction over data.
  • The obvious implementation is too expensive to use.
• A transaction processing monitor manages resources
  • over complex topologies (that is, middleware)
  • to present transactions without the naive cost.

Objectives

• Present uniform, standard I-O via forms managers.
• Perform application-to-middleware transformations.
• Fix APIs.
• Exploit component portability.
• Manage context to simplify services.
• Specialize interfaces for application comfort.
• Provide wizards and other tools.

Engineering

• Spreading out an application over middleware is not easy, and harder to get right.
• “Getting right” means satisfying various system (or pervasive) attributes.
• System attributes are difficult all around: modeling, measuring, maintaining.
• Example system attributes include: portability, performance, reliability, and so on.

Trends

• Increasing spread of middleware functions and services.
• Increasing diversity at all levels.
• Middleware interoperability and (open or independent) standards.

Summary

• Middleware is the 8th layer in the IOS protocol stack.
• The middleware layer distributes both of its clients over the network.
• The principle middleware architectures are client-server, message passing, and publish-subscribe.

References

• Middleware: A Model for Distributed System Service by Philip Bernstein in Communications of the ACM, February, 1996.
• The Internet Operating System: Middleware for Adaptive Distributed Computing by Kaoutar El Maghraoui et.al. in International Journal of High Performance Computing Applications, November 2006.

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This page last modified on 2012 April 23.