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1 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
DistributedSystems
ArchitecturesIS301 – Software Engineering
Lecture # 15 – 2004-10-04M. E. Kabay, PhD, CISSP
Assoc. Prof. Information AssuranceDivision of Business & Management, Norwich University
mailto:[email protected] V: 802.479.7937
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2 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Objectives
To explain the advantages and disadvantages of different distributed systems architectures
To discuss client-server and distributed object architectures
To describe object request brokers and the principles underlying the CORBA standards
To introduce peer-to-peer and service-oriented architectures as new models of distributed computing.
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3 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Topics covered
Multiprocessor architectures Client-server architecturesDistributed object architectures Inter-organizational computing
Today we will use 27 of Prof. Sommerville’s
slides in class
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4 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed systems
Virtually all large computer-based systems are now distributed systems.
Information processing is distributed over several computers rather than confined to a single machine.
Distributed software engineering is therefore very important for enterprise computing systems.
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5 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
System types
Personal systems that are not distributed and that are designed to run on a personal computer or workstation.
Embedded systems that run on a single processor or on an integrated group of processors.
Distributed systems where the system software runs on a loosely integrated group of cooperating processors linked by a network.
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6 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed system characteristics
Resource sharingSharing of hardware and software resources.
OpennessUse of equipment and software from different
vendors.Concurrency
Concurrent processing to enhance performance.Scalability
Increased throughput by adding new resources.Fault tolerance
The ability to continue in operation after a fault has occurred.
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7 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed system disadvantages
ComplexityTypically, distributed systems are more
complex than centralized systems.Security
More susceptible to external attack.Manageability
More effort required for system management.
UnpredictabilityUnpredictable responses depending on the
system organization and network load.
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Distributed systems architectures
Client-server architecturesDistributed services which are called on by
clients. Servers that provide services are treated differently from clients that use services.
Distributed object architecturesNo distinction between clients and servers.
Any object on the system may provide and use services from other objects.
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9 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Middleware
Software that manages and supports the different components of a distributed system. In essence, it sits in the middle of the system.
Middleware is usually off-the-shelf rather than specially written software.
ExamplesTransaction processing monitors;Data converters;Communication controllers.
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10 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Multiprocessor architectures
Simplest distributed system model.System composed of multiple processes
which may (but need not) execute on different processors.
Architectural model of many large real-time systems.
Distribution of process to processor may be pre-ordered or may be under the control of a dispatcher.
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11 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A multiprocessor traffic control system
Traffic lights
Lightcontrolprocess
Traffic light controlprocessor
Traffic flowprocessor
Operator consolesTraffic flow sensors and
cameras
Sensorprocessor
Sensorcontrolprocess
Displayprocess
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12 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Client-server architectures
The application is modeled as a set of services that are provided by servers and a set of clients that use these services.
Clients know of servers but servers need not know of clients.
Clients and servers are logical processes The mapping of processors to processes is
not necessarily 1 : 1.
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13 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A client-server system
s1
s2 s3
s4c1
c2 c3 c4
c5
c6c7 c8
c9
c10
c11
c12
Client process
Server process
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14 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Computers in a C/S network
Network
SC1SC2
CC1 CC2 CC3
CC5 CC6CC4
Servercomputer
Clientcomputer
s1, s2 s3, s4
c5, c6, c7
c1 c2 c3, c4
c8, c9 c10, c11, c12
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Application layers
Presentation layer
Application processinglayer
Data managementlayer
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18 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Thin and fat clients
Thin-clientmodel
Fat-clientmodel Client
Client
Server
Data managementApplication processing
Presentation
Server
Data management
PresentationApplication processing
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21 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A client-server ATM system
Account server
Customeraccountdatabase
Tele-processingmonitor
ATM
ATM
ATM
ATM
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23 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A 3-tier C/S architecture
Client
Server
Datamanagement
PresentationServer
Applicationprocessing
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24 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
An internet banking system
Database server
Customeraccountdatabase
Web serverClient
Client
Account serviceprovision
SQLSQL query
HTTP interaction
Client
Client
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27 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed object architecture
Object request broker
o1 o2 o3 o4
o5 o6
S (o1) S (o2) S (o3) S (o4)
S (o5) S (o6)
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30 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A data mining system
Database 1
Database 2
Database 3
Integrator 1
Integrator 2
Visualiser
Display
Report gen.
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33 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
CORBA application structure
CORBA services
Domainfacilities
Horizontal CORBAfacilities
Applicationobjects
Object request broker
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38 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
ORB-based object communications
o1 o2
S (o1) S (o2)
IDLstub
IDLskeleton
Object Request Broker
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40 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Inter-ORB communications
o1 o2
S (o1) S (o2)
IDLstub
IDLskeleton
Object Request Broker
o3 o4
S (o3) S (o4)
IDLstub
IDLskeleton
Object Request Broker
Network
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45 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Decentralized p2p architecture
n1
n2 n3
n4
n5
n6
n7
n8
n9 n10 n11
n12
n13
n13
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46 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Semi-centralized p2p architecture
Discoveryserver
n1
n2
n3
n4
n5
n6
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49 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Web services
Serviceregistry
Servicerequestor
Serviceprovider
Publish
Bind
Find
service
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53 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Automotive system
User interface
Locator
Discovers carposition
Weatherinfo
Receives requestfrom user
Receiver
Receivesinformation stream
from services
Transmitter
Sends position andinformation request
to services
Radio
Translates digitalinfo stream toradio signal
In-car software system
Mobile Info Service
Facilitiesinfo
Translator
Roadlocator
Trafficinfo
Collates information
Road traffic info
commandgps coord
gpscoord gps coordgps coord
Languageinfo
Infostream
Service discovery
Finds availableservices
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56 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Homework
RequiredBy 11 Oct 2004For 20 points, answer in detail
12.3, 12.8 (@10) [use computer-drawn diagrams for these two]
For 5 points, answer in detail 12.5Optional
By 18 Oct 2004For a maximum of 8 additional points,
answer any or all of12.1, 12.2, 12.4, 12.6 (@2)
Names etc. on upper
right, please
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57 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
DISCUSSION