[Fiware-oasc-etsi] Preliminary proposal for evolution of FIWARE APIs and data models, based on JSON-LD

[Tobias Jacobs]

Hi Gilles,

I have read your proposal on using JSON-LD and I think I have more or less understood it, but I need to discuss with some of my colleagues, who are currently out.

Anyway, my main question is currently how JSON-LD can help to solve the requirement on entity type systems Martin and me have formulated here: https://github.com/telefonicaid/fiware-orion/issues/1516

“
NEC proposes to include in the NGSI 2 specs syntax and semantics for NGSI type ontologies.

An NGSI type ontology expresses

    Which entity types exist in an NGSI system
    Which value types are used by an NGSI system
    Which metadata names are used in an NGSI system

Relations:
o Which entity types have which attributes, and what are the value types of these attributes
o Which entity types are related by a subtype-relationship. Entity Subtypes inherit all attributes from their supertypes
o Which metadata names have which metadata types
o (maybe) which value types can have which metadata

This kind of information can be expressed by an ontology. What we propose is to

    Define an ontology structure, i.e. specify how the above information is to be expressed
    Define a lightweight NGSI base ontology containing o Only the entity type “entity” which is the supertype of all other entities o Basic value types for string, numbers, dates/time, maybe geo-location o Basic metadata like timestamp, accuracy, provider o Basic attributes of entity type “entity” for describing e.g. the entity location

A concrete NGSI system deployment can then extend the base ontology with all the entities/attributes/metadata used within the system. By publishing that ontology, users then know which entity types they can query.
“

If entities are represented as RDF nodes (or, in JSON-LD terms, as JSON objects with an IRI as @id), then of course it is natural to use the @type as a reference to an RDF node representing the entity type. But this does not yet give information about which attributes (JSON-LD: properties) an entity of a specific type can have, what are the value types of these attributes, and what is the supertype of a specific entity type.
As far as I understand  in JSON-LD the @type for nodes is nothing more than a predefined link label.

Then there is also the possibility to use @context objects to describe the attributes (properties) of an entity (node). But the @type property does not link to an @context object but to a node.

Maybe there is a standardized way to represent type hierarchies in RDF, which we can re-use?

Best
Tobias





From: fiware-iot-bounces at lists.fiware.org [mailto:fiware-iot-bounces at lists.fiware.org] On Behalf Of gilles.privat at orange.com
Sent: Donnerstag, 31. Dezember 2015 12:06
To: fiware-ngsi at lists.fiware.org; fiware-iot at lists.fiware.org; fiware-chapter-architects at lists.fiware.org; Fiware-oasc-etsi at lists.fiware.org
Cc: LI Wenbin IMT/OLPS; DANNO Vincent IMT/OLN; EXCOFFIER David IMT/OLPS; RICHARD Francois SCE/SC; MARTIGNE Patricia IMT/OLN; CHIVOT Laurent IMT TECHNO; RIGA Joel IMT/OLPS
Subject: [Fiware-iot] Preliminary proposal for evolution of FIWARE APIs and data models, based on JSON-LD

Dear colleagues
A discussion had been initiated a few months ago by Jose Manuel and Fermin on the Orion GitHub about the use of JSON-LD for the FIWARE API.
We propose to extend this discussion in view of the planned re-standardization of the FIWARE API and data model.
Attached is a draft position paper on how we could rethink the API and make it more appealing to developers, more generic and more evolvable by separating it completely from the data models, precisely by using  JSON-LD.
This is just a basis for starting initiating a discussion, not a definite proposal.
Cordially

[http://www.francetelecom.com/sirius/logos_mail/orange_logo.gif]
Gilles Privat
Senior Scientist
Orange Labs, Grenoble
M2M, Internet of Things, Smart Cities
gilles.privat at orange.com<mailto:gilles.privat at orange.com>
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