Introduction
Dr Simon Blake
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Distributed Information Systems Lecture 1 - Introduction, Lecture notes of Computers and Information technologies
Detailed informtion about Introduction, The course structure, Assessment, Topic list and overview, Key concepts, Distributed System Overview.
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Introduction^ Dr Simon Blake
Topics for this lecture
- The course structure• Assessment• Topic list and overview• Key concepts
–Transparency–Openness–Scalability
- Distributed System Overview
Acknowledgements
Acknowledgements andkind thanks for theirwonderful book to: G.Coulouris, J.Dollimore,T.Kindberg
•^
Lots of material and examples arebased on this book the followingbook
-^
It is essential ready for you all
Addison
Wesley(14 Jun2005)
Distributed Systems: Concepts and Design,
rd 4 edition
2005
G.Coulouris, J.Dollimore,
T.Kindberg
0321263545
Publisher
Title
Date
Author
ISBN
Other useful texts
John Wiley
Client/Server Programming with Java andCorba,
2nd edition.
(Includes CD-ROM with Visigenic's Corbaimplementation 'Visibroker')
1998
R.Orfali, D.Harkey
0-471-24578-X
Prentice Hall
Object-Oriented Client/server InternetEnvironments
1997
A.Umar
0-13-375544-
Prentice Hall
Distributed Operating Systems
1995
A.S.Tanenbaum
0-13-143934-
AddisonWesley
Concurrent Systems: An integratedApproach to Operating Systems, Databasesand Distributed Systems, 2
nd^
edition
1998
J.Bacon
0-201-41677-
Prentice-Hall
Application (Re) Engineering: BuildingWeb-based applications and Dealing withLegacies
1997
A.Umar
0-13-750035-
IDG Books
Corba for Dummies
1998
J.Schettino
0-7645-0308-
McGraw-Hill
Distributed Information Systems: fromClient/Server to Distributed Multimedia
1996
E.Simon
0-07-709076-
McGraw-Hill
Distributed Systems and Networks
2000
W.Buchanan
007 709583 9
Publisher
Title
Date
Author
ISBN
A distributed system
Definition:
“A Distributed System
(DS) consists of a collection of autonomous
computers
linked by a computer network
and equipped with DS
software
“DS software enables computers to coordinate
their activities and to
share
the resources of the system - hardware, software and data.”
“Users of a DS should perceive
a single
, integrated
computing facility
even though it may be implemented
by many computers in different
locations.”
Coulouris et a, 2005
A non-distributed system
Characteristics of a non-distributed system
- One component with non-autonomous parts– Component shared by users all the time– All resources accessible– Software runs in a single process– Single Point of control– Single Point of failure
Wolfgang Emmerich, 1997
A distributed system
Technological enablers of modern DS
- Before the mid 80’s
- Most organizations had only a few systems
- They lacked a way to connect them– They operated independently from one another
- Computers were typically expensive and large
- By the mid-80’s powerful
- Computers were typically expensive and large
- They lacked a way to connect them– They operated independently from one another
- Most organizations had only a few systems
microprocessors
were
developed.
- And… high speed networks began to exist
TODAY: it is easy to combine large numbers ofcomputers with high-speed networks.
A distributed system
Why do DS exist?
- It makes it easy to connect users to
remote resources
- It enables resources sharing with remote users (in a controlled
way)
Key features:
- Hiding the fact that the resources are physically distributed
over a network --
transparency
- Should be an
open system
- Offers services by standard rules that describe the
syntax and semantics of those services
- Should be
scalable
- size, geography, and administration
A distributed system
Transparency “Is defined as the concealment
from the user and the application programmer
of the separation of components in a DS, so that the system is perceived as
a whole
rather than as a collection of independent components”
Coulouris et al
There many different types of transparency:
-^
Access transparency
:^ differences in data representation & how resource is accessed
-^
Location transparency
:^ where a resource is located
-^
Migration transparency
:^ that a resource may move locations
-^
Relocation transparency
:^ that a resource may be moved while in
use
-^
Replication transparency
:^ that a resource is replicated
-^
Concurrency transparency
:^ that a resource may be shared by
competitors
-^
Failure transparency
:^ failure and recovery of a resource
-^
Persistence transparency
:^ whether a software resource is in memory or on disk
A distributed system
Openness
Offers services according to standard rules describingsyntax and semantics of the services.
- Rules are formalized in
protocols
- Services generally specified through
interfaces
- using Interface Definition Language (IDL)
- specify syntax only
- natural language used to describe semantics• allows arbitrary process that needs an interface to talk to
- specify syntax only
another process that provides it
- proper interfaces are complete and neutral
A distributed system
DS enables greater flexibility
- System must be organized as a collection of relatively small and
easily replaceable or adaptable components
- Need for change -^
Business changes
-^
Technology changes
-^
Business drives changes
-^
Technology enables business changes
-^
Component does not provide optimal policy for a specific user orapplications
A distributed system
DS enables scalability in terms of administration
- How to scale across multiple independent
administrative domains
- Conflicting policies
- usage (payment)• management• security
- protect against malice from the new domains– protect against malice from the distributed system -- e.g.
- usage (payment)• management• security
downloaded programs
A distributed system
DS enables scalability in terms of geography
- Existing distributed systems designed for LANs are
based on
synchronous communication
- Communication in WANs is inherently unreliable and
almost always point-to-point
- LANs provide reliable comm based on
broadcasting
-- WAN
needs special location services
- Centralized components prevent geographic scale
What we will study
Topic list
-^
Introduction
-^
Characterisation of Distributed Information Systems
-^
System Models
-^
Networking and Internetworking
-^
Inter-Process Communication
-^
Distributed Objects and Remote Invocation
-^
Constructing a DIS application
-^
Operating System Support
-^
Security
-^
Distributed File Systems
-^
Name Services
-^
Time and Global States
-^
Coordination and Agreement
-^
Transactions and Concurrency Control
-^
Replication
-^
Java EE Application Architectures
-^
Service Orientated Architectures
-^
.NET architecture