[Crm-sig] Fwd: Re: homework

[martin]

Dear All,

Here a better version I just received from Matthew Stiff:

"Properties, such as having a part, an owner or a location, may change 
many times for a single item during its existence. Stating instances of 
such properties for an item in terms of the CRM only means that these 
properties existed during some  particular time-span. Therefore, one 
item may have multiple instances of the same property reflecting an 
aggregation of these instances over its time-span of existence. If more 
temporal details are required, the CRM recommends explicitly describing 
the events of acquiring or losing such property instances, such as E9 
Move etc. By virtue of this principle, the CRM achieves monotonicity 
with respect to an increase of knowledge about the states of an item at 
different times, regardless of their temporal order.

However, for some of these properties many collection databases describe 
the "current" state, such as "current location" or "current owner". 
Using such a "current" state means, that the database manager is able to 
verify the respective reality at the latest date of validity of the 
database. Obviously, this information is non-monotonic, i.e., it 
requires deletion when the state changes. In order to preserve a reduced 
monotonicity, these properties have time-neutral superproperties by 
which respective instances can be reclassified if the validity becomes 
unknown or no longer holds. Therefore the use of such properties in the 
CRM is only recommended if they can be maintained consistently. 
Otherwise, they should be reclassified by their time-neutral 
superproperties. This holds in particular if data is exported to another 
repository."

On 12/11/2012 8:56 ??, martin wrote:
> Dear All,
>
> Here my proposal for a text about temporal validity of properties for
> the CRM introduction:
>
> Properties, such as having a part, an owner or a location, may change 
> many times for a single item during its existence. Stating instances 
> of such properties for an item in terms of the CRM only means that 
> these properties existed at some time-span. Therefore, one item may 
> have multiple instances of the same property reflecting an aggregation 
> of these instances over its time-span of existence. If more temporal 
> details are required, the CRM recommends to explicitly describe the 
> events of acquiring or loosing such property instances explicitly, 
> such as E9 Move etc. By virtue of these principle, the CRM achieves 
> monotonicity with respect to an increase of knowledge about the states 
> of an item at different times regardless of their temporal order.
>
> However, for some of these properties many collection databases 
> describe the "current" state, such as "current location" or "current 
> owner". Using such a "current" state means, that the database 
> maintainer is able to verify the respective reality at the latest date 
> of validity of the database. Obviously, this information is 
> non-monotonic, i.e., it requires deletion when the state changes. In 
> order to preserve a reduced monotonicity, these properties have 
> time-neutral superproperties by which respective instances can be 
> reclassified if the validity becomes unknown or no more holds. 
> Therefore the use of such properties in the CRM is only recommended if 
> they can be maintained consistently. Otherwise, they should be 
> reclassified by their time-neutral superproperties. This hold in 
> particular if data are exported to another repository.
>

-- 

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  Dr. Martin Doerr              |  Vox:+30(2810)391625        |
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                                |  Email: martin at ics.forth.gr |
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