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OUTLINE
Review Transparencies in DOS Categorization Degree of Transparency Summary Reference
Review
Evolution of Modern Operating Systems What is DOS? Goals of DOS
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
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.
Goals of DOS
Efficiency Flexibility Consistency Robustness
OUTLINE
Review Transparencies in DOS Categorization Degree of Transparency Reference
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.
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.
Access Transparency
The ability to access both local and remote system objects in a uniform way.
Example: NFS
Location Transparency
Name TransparencyUsers have no awareness of object
locations (physical location) "The network is the computer"
Migration Transparency
Resources could be free to move from one location to another without having their names changed
Example: Cell phone & BSC, roaming
Example
Communication with your friends…. Access Location Migration Access location Migration are interrelated
Failure Transparency
Applications should be able to complete their task despite failures occurring in certain parts of the system.
Fault tolerance Example: backup database
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)
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
Performance Transparency
Load variation should not lead to performance degradation. This could be achieved by automatic reconfiguration as response to changes of the load.
Parallelism Transparency
This permits parallel activities without users knowing how, where, and when these activities are carried out by the systems.
Scaling (Size) Transparency
Can expand in scale(incremental growth) without change to system's structure or application algorithms.(Hardware)
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.
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.
Persistence Transparency
Hide whether a (software) resource is in memory or on disk.
Relocation transparency
Should a resource move while in use, this should not be noticeable to the end user.
OUTLINE
Review Transparencies in DOS Categorization Degree of Transparencies Summary Reference
Goal: Flexibility
Access
location
migration
size
revision
Goal: Consistency
Access
Replication
Performance
Goal: Robustness
failure
replication
size
revision
Goal: Efficiency
Concurrency
Parallelism
Performance
OUTLINE
Review Transparencies in DOS Classification Degree of Transparencies Summary Reference
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
Trade-off
Shielding the system-dependent information from the users is basically a trade-off.
OUTLINE
Review Transparencies in DOS Classification Degree of Transparencies Summary Reference
Summary
What is Transparency?
Categorization
Trade-off
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)
Thanks and Apologize
Thank you!谢谢 ! shukria
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
