[Crm-sig] homework

martin martin at ics.forth.gr
Mon Nov 12 20:56:31 EET 2012


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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