Fundamentals Stream Session : Emerging Trends in Distributed Systems

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Fundamentals Stream Session Emerging Trends in
Distributed Systems
Distributed Systems

• CSC 253
• Gordon Blair, François Taïani

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Overview of the Session

• From distributed objects to components
• Introduction to components
• Rationale
• Focus on Enterprise Java Beans
• Key role of containers
• Other key trends
• Mobile computing
• Multimedia
• Multiplicity

Associated Reading Tanenbaum and van Steen,
chapter 2 (pp.119-130)
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From Distributed Objects to Components

• What is a component Szyperski?

a unit of composition with contractually
specified interfaces and explicit context
dependencies only
in this context, a component can be deployed
independently and is subject to third-party
composition
Also typically coarse-grained and binary
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Rationale for Components

• Time to market
• Improved productivity/ reduced complexity
• Emphasis on reuse
• Programming by assembly (manufacturing) rather
  than development (engineering)
• Reduced skills requirement
• Key benefit on server side development?
• (See EJB later)

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Composition

• Components and composition
• Composition is the principal means of
  construction, extension and reuse in
  component-based software development
• C.F. (implementation) inheritance in
  object-oriented approaches

Components are for composition
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Components Key Players

• The OMG and components
• Emerging CORBA v3 standard featuring the CORBA
  Component Model (CCM)
• Microsoft and components
• Development of COM/ DCOM, COM and, more
  recently, .NET
• SUN and components
• Development of Enterprise Java Beans

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A Brief Look at Enterprise Java Beans

• What is EJB?
• A server-side component architecture for Java
• Based on the concept of a container
• Offers implicit distributed systems management
• Formalises the interface between a managed bean
  (EJB) and its container
• Event (callback) interface
• Services expected in the container
• Deployment using JAR files

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A Word from SUN...
The Enterprise JavaBeans architecture is a
component architecture for the development and
deployment of component-based distributed
business applications. Applications written using
EJB are scalable, transactional, and multi-user
secure. These applications mat be written once,
and then deployed on any server platform that
supports the EJB specification.
C.F. Programming the middle tier of a 3-tier
architecture
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A Closer Look at Containers

• Distributed systems management
• Declarative and implicit transaction service
• Declarative and implicit security service
  (essentially access control)
• Other services
• Activation and passivation, persistence
• Life cycle management
• Container metadata (introspection)
• Packaging and deployment

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A Closer Look at Containers (continued)
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Enterprise JavaBeans An Evaluation

• Advantages
• Disadvantages

http//java.sun.com/products/ejb/white/white_paper
.html
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Other Key Trends

• Multimedia
• Support for continuous media
• Implications for distributed systems
• Mobility
• Supporting the mobile user
• Implications for distributed systems
• Multiplicity
• Supporting a wide variety of application domains
• Implications for distributed systems

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Multimedia

• What is multimedia?
• The need to support a variety of media types in
  an integrated manner
• The challenge of multimedia
• Support for continuous media
• Audio, video, animation, etc
• Support for quality of service (QoS)
• Static QoS management
• Dynamic QoS management

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Implications for Distributed Systems

• Currently there is little or no support for
  continuous media in distributed systems platforms
• Developers must resort to proprietary solutions
• Clear need for multimedia middleware with
  intrinsic support for streaming data
• Currently there is little or no support for
  quality of service
• Again, pressure for ad-hoc or proprietary
  solutions
• Clear need for co-ordinated quality of service
  management
• Network
• Operating system
• Middleware

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Mobility

• What is mobile computing?
• Supporting computer users on the move
• Important role of ubiquitous networking including
  wireless networks
• The challenge of mobility
• Support for disconnected operation
• C.f. Coda
• Support for context awareness
• E.g. location awareness
• Support for adaptation
• E.g. dealing with drop in network connectivity

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Multiplicity

• What is multiplicity?
• We are entering a stage of extreme heterogeneity
• Distributed systems technologies such as
  middleware are being applied in a rapidly
  increasing set of application domains and
  operational settings
• Middleware itself is becoming part of the problem
• The solution?
• Support for configurability
• Support re-configurability
• Support for autonomic management
• Radical re-think of interoperability

http//www.comp.lancs.ac.uk/computing/research/mpg
/reflection/
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Expected Learning Outcomes

• At the end of this session
• You should have an awareness of some of the key
  trends and research directions in distributed
  systems
• You should understand the rationale for the
  emergence of component-based middleware and also
  appreciate the key concepts underpinning such
  technologies, particularly containment
• You should have a general awareness of the
  challenges imposed by areas such as multimedia,
  mobility and multiplicity and the implications
  that this has for distributed systems design

Thank you for your attention on the course