Re: Equality of RDF bags

Hi Martin,

Forgive a quick nitpick:

On 28/10/2011 19:24, Martin Hepp wrote:
> Note that two blank nodes having the same attributes and the same type may still represent two distinct entities with a different identity. In particular if you think of changing RDF data (SPARUL updates, this can be an important distinction.
>
> For instance, if in GoodRelations, two items momentarily have the same price, e.g.
>
> foo:offer1 a gr:Offering;
>      gr:name "ACME Laptop" ;
>      gr:hasPriceSpecification [
>          a gr:UnitPriceSpecification;
>      	gr:hasCurrency "USD"^^xsd:string;
>      	gr:hasCurrencyValue "9.90"^^xsd:float;
>      	gr:hasUnitOfMeasurement "C62"^^xsd:string ] .
>
> foo:offer2 a gr:Offering;
>      gr:name "ACME Semantic Web Services Book" ;
>      gr:hasPriceSpecification [
>          a gr:UnitPriceSpecification;
>      	gr:hasCurrency "USD"^^xsd:string;
>      	gr:hasCurrencyValue "9.90"^^xsd:float;
>      	gr:hasUnitOfMeasurement "C62"^^xsd:string ] .
>
> Then you should not infer that both have the same entity representing the unit price, because these may evolve differently, so you should not infer that they have the same price, but just that their anonymous price node has currently the exact same attributes. But sameness in type and attributes does not say anything about whether this is the same entity, as long as the descriptions of each node are incomplete, which is always the case.

RDF semantics would not consider the two blank-nodes in the example to 
be the "same entity" since one is the price-specification of foo:offer1 
and the other is the price-specification of foo:offer2. This 
distinguishes them apart: the result of merging the two examples above 
is lean.

...this doesn't necessarily invalidate your original point about 
blank-nodes, but you need different examples.

Cheers,
Aidan

Received on Monday, 31 October 2011 19:40:25 UTC