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Re: How do I bundle in tangential metadata?

From: Nathan Ridley <axefrog@gmail.com>
Date: Sat, 21 Mar 2015 18:12:08 +1000
Message-ID: <CAMKTGkYdZsbC9NV76hHTMhEKeGqd9dZ8k0VZ4rVO=NUx8qP=gg@mail.gmail.com>
To: "public-linked-json@w3.org" <public-linked-json@w3.org>
Hi Julian, sorry for the slow reply; I've been off work for a few days.
Thanks for your insights; they've given me plenty to think about. Do you
have any opinion on Hydra as it compares to HAL? Clearly Hydra is more
ambitious than HAL in terms of what it offers, though I don't yet have a
sense of how the two compare in practice, other than the fact that HAL
appears to offer a simplified subset of what Hydra offers.


Hi Nathan,
> I think this is an interesting question, and one which it took me a while
> to unpick when I started building linked data APIs. The thing to remember
> is that if you are exposing linked data via a REST interface then, as you
> note, URLs are typically being used for two fundamentally different
> concerns - one relating to state and another relating to behaviour:
> 1. Thinking about a resource in REST terms, i.e. as a finite state
> machine, hypermedia is used to drive the state transitions - i.e. it is a
> behavioural concern.
> 2. Thinking about a resource in linked data terms, URLs are used to fully
> qualify encoded data - i.e. they are a state concern.
> I see these as entirely complimentary: you just need to be clear about
> when you are using URLs as a state transfer mechanism vs when you are using
> URLs for data encoding.
> If you think about the program sequence of a client requesting a resource
> from a linked data API, the way in which the API adds value to the program
> flow is typically by reducing client-server coupling and by making the
> graph into something as consumer-friendly as possible. In my experience
> that has meant merging state transfer/API navigability identifiers into the
> response, and also simplifying the graph e.g. by flattening/dereifying
> provenance information, etc. Typically my API clients are web-based and
> they want something as standard JSON-like as possible. For such
> representations, my standard pattern is now to use:
> 1. HAL (http://stateless.co/hal_specification.html) for the behavioral
> concerns
> 2. JSON-LD for the resource state encoding
> 3. JSON-LD framing to make the response look as close to standard JSON as
> possible
> 4. a declared MIME type of 'application/hal+json'
> 5. a Link header which references the associated external json-ld contexts.
> That gives all the benefits of linked data for those clients who care
> about it, but on more of an 'opt-in' basis where other consumers who only
> care about late-binding to your API to protect against future versioning
> issues can basically treat it as a standard RESTful JSON interface.
> cheers
> Julian
Received on Saturday, 21 March 2015 08:12:36 UTC

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