Transparency Wang, Yang [email protected]. edu.
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Transcript of Transparency Wang, Yang [email protected]. edu.
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OUTLINE
Review Transparencies in DOS Categorization Degree of Transparency Summary Reference
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Review
Evolution of Modern Operating Systems What is DOS? Goals of DOS
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Evolution of Modern Operating Systems
1st Generation: Centralized Operating System
2nd Generation: Network Operating System 3rd Generation: Distributed Operating
System 4th Generation: Cooperative autonomous
System
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Definition of DOS
We define a DOS as an integration of system services ,presenting a transparent view of a multiple computer system with distributed resources and control.
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Goals of DOS
Efficiency Flexibility Consistency Robustness
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OUTLINE
Review Transparencies in DOS Categorization Degree of Transparency Reference
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Definition of Transparency in DOS
Concealment from the user and the application programmer of the separation of components in a distributed system, so that the system is perceived as a whole than rather as a collection of independent components.
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Compare
In software engineering, it is also considered good practice to develop or use abstraction layers for database access, so that the same application will work with different databases; here, the abstraction layer allows other parts of the program to access the database transparently.
In object-oriented programming, transparency is facilitated through the use of interfaces that hide actual implementations through different classes.
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Access Transparency
The ability to access both local and remote system objects in a uniform way.
Example: NFS
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Location Transparency
Name TransparencyUsers have no awareness of object
locations (physical location) "The network is the computer"
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Migration Transparency
Resources could be free to move from one location to another without having their names changed
Example: Cell phone & BSC, roaming
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Example
Communication with your friends…. Access Location Migration Access location Migration are interrelated
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Failure Transparency
Applications should be able to complete their task despite failures occurring in certain parts of the system.
Fault tolerance Example: backup database
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Replication Transparency
The system is free to make additional copies of files and other resources (for purpose of performance and/or reliability), without the users noticing.
Consistency between copies (DNS master ,slave)
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Concurrency Transparency
The users will not notice the existence of other users in the system (even if they access the same resources)
Similar to time-sharing system
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Performance Transparency
Load variation should not lead to performance degradation. This could be achieved by automatic reconfiguration as response to changes of the load.
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Parallelism Transparency
This permits parallel activities without users knowing how, where, and when these activities are carried out by the systems.
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Scaling (Size) Transparency
Can expand in scale(incremental growth) without change to system's structure or application algorithms.(Hardware)
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Revision Transparency
This refers to the vertical growth of systems as opposed to the horizontal growth as in scalable transparency. Revision of software not visible to users.
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Security transparency
Negotiation of cryptographically secure access of resources must require a minimum of user intervention, or users will circumvent the security in preference of productivity.
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Persistence Transparency
Hide whether a (software) resource is in memory or on disk.
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Relocation transparency
Should a resource move while in use, this should not be noticeable to the end user.
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OUTLINE
Review Transparencies in DOS Categorization Degree of Transparencies Summary Reference
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Goal: Flexibility
Access
location
migration
size
revision
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Goal: Consistency
Access
Replication
Performance
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Goal: Robustness
failure
replication
size
revision
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Goal: Efficiency
Concurrency
Parallelism
Performance
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OUTLINE
Review Transparencies in DOS Classification Degree of Transparencies Summary Reference
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Degree
Distribution transparency is generally preferable, but not always a good idea:
– It is undesirable to hide the location of the printer from its users
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Trade-off
Shielding the system-dependent information from the users is basically a trade-off.
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OUTLINE
Review Transparencies in DOS Classification Degree of Transparencies Summary Reference
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Summary
What is Transparency?
Categorization
Trade-off
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Some related articles
[1] Application-Transparent Fault Tolerance in Distributed Systems, Thomas Becker
[2]On the Structuring of Distributed Systems: The argument for mobility, Todd.
[3]Name Transparency in very large scale Distributed file systems, Richard G. Guy et al
[3]http://en.wikipedia.org/wiki/Transparency_(computing)
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Thanks and Apologize
Thank you!谢谢 ! shukria
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References[1]A. S. Tanenbaum, “Distributed Operating Systems”,Prentice
Hall, pp.22-25.[2]R. Chow,T. Johnson, “Distributed Operating Systems &
Algorithms”, Addison Weley, pp.29-32.[3]J. Wein, “Parallel & Distributed Systems”[4]B. Karp, “RPC & Transparency”,UCL Computer Science,2006[5]Y. Lu,”Distributed Operating Systems”,UNL[6]J. Holliday,”Distributed Computing”,SCU[7]B. Karp, S. Hailes,”Distributed Systems & Security:An
Introduction,UCL Computer Science,2006