/[gzz]/manuscripts/pointers/article.rst
ViewVC logotype

Diff of /manuscripts/pointers/article.rst

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 1.58 by benja, Sat Nov 1 21:10:43 2003 UTC revision 1.59 by benja, Sat Nov 1 21:23:39 2003 UTC
# Line 85  from any host that has a copy. This woul Line 85  from any host that has a copy. This woul
85  and increase availability. However, if the Web worked like  and increase availability. However, if the Web worked like
86  a file-sharing system, Web pages could never be updated.  a file-sharing system, Web pages could never be updated.
87    
88    While many file-sharing systems provide URIs
89    for particular versions of a file, using cryptographic hashes
90    (e.g., [XXXrefs]), these files cannot be updated;
91    a new version would have a different hash, and thus
92    a different URI. In file-sharing systems, updating
93    would be useful for media files like the e-books
94    distributed by Project Gutenberg [XXXref], which
95    are occasionally updated to fix typographic errors.
96    
97  XXX  XXX
98    
99  .. Standing on the shoulders of giants: Example of Web links rotting away  .. Standing on the shoulders of giants: Example of Web links rotting away
# Line 133  and links should continue to work. Line 142  and links should continue to work.
142    
143     History of location-dependence: `TBL ref`_ (like in HT'03 paper)     History of location-dependence: `TBL ref`_ (like in HT'03 paper)
144    
145  This can be accomplished by replacing URIs that include  .. <<<This can be accomplished by replacing URIs that include
146  a server name by URIs that are     a server name by URIs that are
147    
148  - location-independent: do not refer to a particular server     - location-independent: do not refer to a particular server
149    that the file is to be downloaded from;       that the file is to be downloaded from;
150  - semantic-free: don't include human-readable information;     - semantic-free: don't include human-readable information;
151    if an identifier is semantic-free, there is no incentive       if an identifier is semantic-free, there is no incentive
152    to change it when a site is re-designed;       to change it when a site is re-designed;
153  - self-verifying: after downloading an alleged copy of a document,     - self-verifying: after downloading an alleged copy of a document,
154    there is a cryptographical algorithm to test whether       there is a cryptographical algorithm to test whether
155    this is *really* a copy of this document.       this is *really* a copy of this document.>>>
156    
157  The most prominent example are cryptographic hashes.  .. <<<In 1996, Tim Berners-Lee [name-myth]_ argued that
158  A file identified by a cryptographic hash     using location-independent, semantic-free identifiers
159  can be downloaded from any server that has a copy; the client     is not viable on a global scale:
160  can then check the integrity of the file by checking it against the hash.     "[I]f you put information in a name, it decreases its longevity;
161       if you don't you can't dereference it to a resource.">>>
162  .. <<<Self-verifying means that given the identifier and a file,  
163     a client can check that the file matches the identifier.>>>  .. <<<However, as observed in [fallenstein03storm]_,
164       with the advent of efficient peer-to-peer lookup mechanisms such as
165  .. <<<(If the hashes do not match, the client can try a different server.)     distributed hashtables (DHTs), this observation
166     This way, a page's URI never needs to change.>>>     is no longer true. A DHT is quite able to resolve a
167       hash-based identifier on a global scale,
168  In 1996, Tim Berners-Lee [name-myth]_ argued that     as evidenced by applications like the Cooperative
169  using location-independent, semantic-free identifiers     File System (CFS, [dabek01widearea]_) and
170  is not viable on a global scale:     the Overnet file sharing client [overneturl]_.>>>
 "[I]f you put information in a name, it decreases its longevity;  
 if you don't you can't dereference it to a resource."  
   
 However, as observed in [fallenstein03storm]_,  
 with the advent of efficient peer-to-peer lookup mechanisms such as  
 distributed hashtables (DHTs), this observation  
 is no longer true. A DHT is quite able to resolve a  
 hash-based identifier on a global scale,  
 as evidenced by applications like the Cooperative  
 File System (CFS, [dabek01widearea]_) and  
 the Overnet file sharing client [overneturl]_.  
171    
172  .. SFR (semantic-free referencing) not all that close,  .. SFR (semantic-free referencing) not all that close,
173     though semantic-free idea shared (SFR takes along     though semantic-free idea shared (SFR takes along
# Line 188  the Overnet file sharing client [overnet Line 186  the Overnet file sharing client [overnet
186    
187  .. Proposal: A location-independent Web <<<(closest thing is Freenet (ref))>>>  .. Proposal: A location-independent Web <<<(closest thing is Freenet (ref))>>>
188    
 We propose, then, to build a location-independent Web  
 based on self-verifying identifiers.  
   
189  .. <<<The project that is currently closest to this goal is Freenet,  .. <<<The project that is currently closest to this goal is Freenet,
190     a XXX>>>     a XXX>>>
191    
# Line 203  based on self-verifying identifiers. Line 198  based on self-verifying identifiers.
198     - Verifiable     - Verifiable
199     - Same namespace for local and for non-local data     - Same namespace for local and for non-local data
200    
 Using hash-based addressing in such a scheme has several benefits:  
   
 - Pages can be moved between servers without breaking links.  
 - Links continue to work as long as *anybody* keeps a copy  
   of their targets, even if the original publisher does not  
   maintain the Web page any longer.  
 - Downloaded files can keep their global identifiers.  
   Links between two downloaded Web pages automatically work.  
 - It is possible to implement load-balancing schemes in which  
   a user downloads a page from anybody who happens to have a copy.  
 - Different networks can be used to download a file. XXX  
   
201  .. <<<Other projects exploit some of the advantages of hash-based  .. <<<Other projects exploit some of the advantages of hash-based
202     (storage systems: CFS, PAST; web caching: Squirrel),     (storage systems: CFS, PAST; web caching: Squirrel),
203     but don't address the Web.>>>     but don't address the Web.>>>
# Line 231  Using hash-based addressing in such a sc Line 214  Using hash-based addressing in such a sc
214  .. However, there's a problem with this: versioning -----  .. However, there's a problem with this: versioning -----
215     Basic problem: Hash-based addressing allows no updates     Basic problem: Hash-based addressing allows no updates
216    
 However, a document refered to by a cryptographic hash  
 can obviously not be changed (without making it a different document,  
 refered to by a different hash). For most Web pages, this is not  
 acceptable [#academic-articles-hashlinking]_. In this paper,  
 we examine solutions to this problem that keep the desirable properties  
 of hash-based addressing.  
   
217  .. Contributions; structure of this paper ----  .. Contributions; structure of this paper ----
218    
219  .. Main contrib: Pointer records for implementing updating  .. Main contrib: Pointer records for implementing updating
# Line 614  We would like to thank Hermanni Hyyti\"a Line 590  We would like to thank Hermanni Hyyti\"a
590  .. [#rtg-links] ``http://www.seds.org/spaceviews/cassini/rtgpages.html``.  .. [#rtg-links] ``http://www.seds.org/spaceviews/cassini/rtgpages.html``.
591     All links dereferenced on October 27th, 2003.     All links dereferenced on October 27th, 2003.
592    
593  .. [#academic-articles-hashlinking] A notable exception  .. .. [#academic-articles-hashlinking] A notable exception
594     may be academic articles, in which references to other articles        may be academic articles, in which references to other articles
595     are ideally to an immutable version, and in which references        are ideally to an immutable version, and in which references
596     are generally not circular, making this domain map neatly        are generally not circular, making this domain map neatly
597     to the properties of hash-based referencing.        to the properties of hash-based referencing.
598     XXX Except for "in press", "unpublished manuscripts", ...        XXX Except for "in press", "unpublished manuscripts", ...
599    
600    
601    

Legend:
Removed from v.1.58  
changed lines
  Added in v.1.59

savannah-hackers-public@gnu.org
ViewVC Help
Powered by ViewVC 1.1.26