Re: More History comments

Tansley, Robert wrote:

>>Tansley, Robert wrote:
>>
>>    
>>
>>>This looks fine, until you actually try and change something.  Say I 
>>>add a new bitstream, BITS2, to BND1.  I've shown this in that nasty 
>>>orange colour.  This obviously consistutes a change in BND1; 
>>>      
>>>
>>you can't 
>>    
>>
>>>just draw another hasPart arc between BND1:1 and BITS2:1, since you 
>>>would never be able to tell that BND1 in one situation 
>>>      
>>>
>>contained only 
>>    
>>
>>>BITS1.  So, you create a new situation for BND1, called BND1:2, and 
>>>have hasPart arcs between that and BITS1:1 and BITS2:1.  
>>>      
>>>
>>(This assumes 
>>    
>>
>>>that the situation of BITS1 is not changed by virtue of the 
>>>      
>>>
>>fact that 
>>    
>>
>>>the Bundle it is in has changed.)
>>>
>>>      
>>>
>>This is only a problem for content based identifiers (see my rambling 
>>answer to Mark).  When using resource identifiers the two 
>>instances of 
>>BND1:1 are distinct, so there is no confusion between the two chains.
>>
>>Collapsing all nodes that have the same contents by using 
>>content based 
>>identifiers is an invalid optimization, as this use case shows (among 
>>others.)
>>    
>>
>
>
>Hi Kevin,
>
>I'm afraid I really don't understand what you've said here.  Which response to Mark are you talking about?  BND1:1 is a single node in the graph.  So you might have in two separate parts of the History data,
>
>BND1:1  -- hasPart -->  BITS1:1
>
>BND1:1  -- hasPart -->  BITS2:1
>
>By definition, aren't the two BND1:1's the same node?  Do I have some serious misunderstanding about the basics of RDF here?
>
> Robert Tansley / Hewlett-Packard Laboratories / (+1) 617 551 7624
>  
>
The question is why you decided to use BND1:1 rather than BND1:2.  If 
the choice of BND1:1 was required because the resource at that node is 
identified by a content based identifier, then information has been lost 
about the distinct nature of the two instances.  The graph looks wrong; 
the second chain is logically independent of the first, yet you've 
combined the nodes early in the chain, dividing them only where the 
content has changed.  I think you instead should consider the instance 
chain to be independent of the content (see attachment.)

-- 
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   Kevin Smathers                kevin.smathers@hp.com    
   Hewlett-Packard               kevin@ank.com            
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