Hi // Comments on the Hydra spec

Hi,



I’m a French PhD student. I started my thesis last January in Germany at the university of Passau and in relation with Siemens, in Munich. In the context of my PhD –which is about semantic technologies for the Web of Things–, I heard about both Hydra and LDF, so I thought it might be wise to follow the conversations on this mailing-list. I’m also part of the W3C Web of Things Interest Group.



As I read the Hydra specification document, I asked myself several things:

·         hydra:Resource and hydra:Class are instance of each other. Being an instance of a Resource means being dereferenceable. In which case would you need to access the resource hydra:Class itself? I understood that resource classes should be dereferenceable, as well as resources. But if you define “hydra:Class rdfs:subClassOf hydra:Resource”, this constraint is also semantically fulfilled, since all instances of hydra:Class are instances of hydra:Resource. Was your choice made on purpose?

·         Similarly, in the issue tracker demo, resource classes are defined as instances of hydra:Class (Hydra:Collection in the first place). It can’t figure out why. If I want to do some matchmaking over the API (with the help of reasoning), I would then need to see resource classes as sets of individuals, not as individuals themselves. Is there a particular reason why you went for such a design?

·         Quick remark: the section “3. Hydra at a Glance” is definitely helpful but I’m not sure the current diagram is the best one can make. Why not using a representation that is closer to the RDFS UML profile? I’d prefer, for instance, that arrows carry the property name rather than putting it under the class definition. Moreover, It is a bit confusing that hydra:Collection is an orphan node in the diagram. Why not linking it to hydra:Class?



(I may take long to react if you ask me anything  back, I apologize in advance.)



All the best,

Victor Charpenay



Siemens AG

Corporate Technology

Research and Technology Center

CT RTC NEC ITH-DE

Otto-Hahn-Ring 6

81739 München, Deutschland

mailto:victor.charpenay@siemens.com



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