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revision 1.95 by benja, Mon Nov 3 17:09:23 2003 UTC revision 1.96 by benja, Mon Nov 3 17:20:17 2003 UTC
# Line 6  What's missing: Why isn't the Web runnin Line 6  What's missing: Why isn't the Web runnin
6  Abstract  Abstract
7  ========  ========
8    
9  File-sharing systems save bandwidth and increase availability  Filesharing systems save bandwidth and increase availability
10  because there is no single point of failure for a file.  because there is no single point of failure for a file.
11  This would be desirable on the Web.  This would be desirable on the Web.
12  However, most current P2P systems have no facility  However, most current P2P systems have no facility
13  for updating documents, and those that do  for updating documents, and those that do
14  require keeping the current version as state in the network.  require keeping the current version as state in the network.
15  This loses a major benefit of file-sharing:  This loses a major benefit of filesharing:
16  To keep a version of a Web page available,  To keep a version of a Web page available,
17  it should suffice to keep a copy of it on your computer.  it should suffice to keep a copy of it on your computer.
18    
19  In this paper, we present a simple versioning mechanism usable  In this paper, we present a simple versioning mechanism usable
20  for a P2P Web as well as for file-sharing,  for a P2P Web as well as for filesharing,
21  and P2P-based software distribution and upgrading,  and P2P-based software distribution and upgrading,
22  and serve as a common versioning model integrating  and serve as a common versioning model integrating
23  separate P2P networks.  separate P2P networks.
# Line 47  Introduction Line 47  Introduction
47  .. Introduce location-independent Web idea (citing  .. Introduce location-independent Web idea (citing
48     benefits from hash-based addressing)---     benefits from hash-based addressing)---
49    
50  If the Web worked like a file-sharing system, there would be  If the Web worked like a filesharing system, there would be
51  no central point of failure for a Web page; it could be downloaded  no central point of failure for a Web page; it could be downloaded
52  from any host that has a copy. This would save bandwidth  from any host that has a copy. This would save bandwidth
53  and increase availability. However, if the Web worked like  and increase availability. However, if the Web worked like
54  a file-sharing system, Web pages could never be updated.  a filesharing system, Web pages could never be updated.
55    
56  Some file-sharing systems offer URIs for files (e.g., [XXXref]).  Some filesharing systems offer URIs for files (e.g., [XXXref]).
57  These URIs are based on the files' cryptographic hashes.  These URIs are based on the files' cryptographic hashes.
58  A new version of a Web page would have a different hash,  A new version of a Web page would have a different hash,
59  and thus a different URI.  and thus a different URI.
60    
61  There are a few (non-file-sharing) P2P systems  There are a few (non-filesharing) P2P systems
62  that do offer an update mechanism. *CFS* [dabek01widearea]_  that do offer an update mechanism. *CFS* [dabek01widearea]_
63  is a file system based on Chord [stoica01chord]_, storing  is a file system based on Chord [stoica01chord]_, storing
64  data in a distributed hashtable (DHT). CFS identifies  data in a distributed hashtable (DHT). CFS identifies
# Line 109  is to have a centralized server keep tra Line 109  is to have a centralized server keep tra
109  of a document, such as in the *Content-Addressable Web*  of a document, such as in the *Content-Addressable Web*
110  proposal [content-addressable-web]_, in which clients download  proposal [content-addressable-web]_, in which clients download
111  a file's hash through HTTP (using an HTTP URI),  a file's hash through HTTP (using an HTTP URI),
112  then download the file through, e.g., a file-sharing network.  then download the file through, e.g., a filesharing network.
113  This provides some of the efficiency advantages of a P2P Web.  This provides some of the efficiency advantages of a P2P Web.
114  However, there is still a single point of failure, and  However, there is still a single point of failure, and
115  links still break when pages move to a different directory  links still break when pages move to a different directory
116  or Web server.  or Web server.
117    
118  In a file-sharing system, a file remains accessible  In a filesharing system, a file remains accessible
119  as long as there is a copy on any of the participating hosts.  as long as there is a copy on any of the participating hosts.
120  None of the above versioning systems have this property.  None of the above versioning systems have this property.
121  In CFS, version information is stored in the DHT, and only  In CFS, version information is stored in the DHT, and only
# Line 158  a single point of failure (XXX and censo Line 158  a single point of failure (XXX and censo
158  .. <<<We don't propose that every byte of information ever published  .. <<<We don't propose that every byte of information ever published
159     on the Web has to be kept around forever. However,     on the Web has to be kept around forever. However,
160     we do believe that as long as someone does keep a copy,     we do believe that as long as someone does keep a copy,
161     data should remain accessible, like in a file-sharing system,     data should remain accessible, like in a filesharing system,
162     and links should continue to work.>>>     and links should continue to work.>>>
163    
164  .. <<<Other projects exploit some of the advantages of hash-based  .. <<<Other projects exploit some of the advantages of hash-based
# Line 279  pointer records Line 279  pointer records
279  are treated just as normal data files  are treated just as normal data files
280  and may reside on (and be downloaded from) any host.  and may reside on (and be downloaded from) any host.
281    
282  For example, a file-sharing system could, for every versioned  For example, a filesharing system could, for every versioned
283  file ``f``, store two companion file ``f.version``  file ``f``, store two companion file ``f.version``
284  and ``f.charter``, containing the charter and pointer record  and ``f.charter``, containing the charter and pointer record
285  associated with this version of this file. The file-sharing  associated with this version of this file. The filesharing
286  application could then serve this information to other peers  application could then serve this information to other peers
287  searching for versions of this document. It could also use it  searching for versions of this document. It could also use it
288  to notify the user when new versions of the file become available.  to notify the user when new versions of the file become available.

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