Re: [core] Modernized Link Format

Jim Schaad <ietf@augustcellars.com> Fri, 26 October 2018 22:45 UTC

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From: Jim Schaad <ietf@augustcellars.com>
To: 'Klaus Hartke' <hartke@projectcool.de>
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Subject: Re: [core] Modernized Link Format
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Klaus,

Thanks for this pointer, I have read through this and decided to try and figure out how I think things work based on the document.  For this purpose I just took two of the responses from the resource directory interop and tried to put them into CoRAL


Example #1
The big question that I have here is the fact that I am using the base directive multiple times  I believe that this is correct.

    <coaps://new.example.com:5684/temp>;rt="temperature";ct=0
    <coaps://new.example.com:5684/light>;rt="light-lux";ct=0
    <coaps://new.example.com:5684/t>;anchor="coaps://new.example.com:5684/sensors/temp";rel="alternate"
    <http://www.example.com/sensors/t123>;anchor="coaps://new.example.com:5684/sensors/temp";rel="describedby"
    <coap://[2001:db8:4::1]/light/left>;rt="light";ct=0
    <coap://[2001:db8:4::1]/light/middle>;rt="light";ct=0
    <coap://[2001:db8:4::1]/light/right>;rt="light";ct=0

************************************

#base <coaps://new.example.com:5684>
#using attr = <http://TBD/>
<temp> {
    attr:rt "temperature"
    attr:ct "0"
}
<light> {
    attr:rt "light-lux"
    attr:ct "0"
}
<t> {
    alternate <coaps://new.example.com:5684/sensors/temp"
    describedby <coaps://new.example.com:5684/sensors/temp>
}
#base <coap://[2001:db8:4::1]
<light/left> {
    attr:rt "light"
    attr:ct "0"
}
<light/middle> {
    attr:rt "light"
    attr:ct "0"
}
<light/right>  {
    attr:rt "light"
    attr:ct "0"
}

**********************************

This example is a bit more difficult for me to know if it is correct - The anchor would, possibly, be used to resolve the URI but I note that anchor is explicitly not allowed to be an attribute of the link so I think this is the correct behavior but I am not sure.

</sensors/temp>;ct=41;rt="temperature-c";if="sensor";anchor="coap://spurious.example.com:5683"
</sensors/light>;ct=41;rt="light-lux";if="sensor"

*********************************

#using attr = <http://TBD/>
<coap://spurious.example.com:5683/sensors/temp> {
    attr:rt "temperature-c"
    attr:if "sensor"
}
<sensors/light> {
    attr:rt "light-lux"
    attr:if "sensor"
}


One last item - The current CBOR encoding plays games with a couple of different attributes - specifically the content type where it uses either an integer or an array of integers as the value.  I am not sure if you can have an attribute occur multiple times or not.  (Maybe ditto with links?) 

Jim


> -----Original Message-----
> From: Klaus Hartke <hartke@projectcool.de>
> Sent: Sunday, October 21, 2018 10:29 AM
> To: Jim Schaad <ietf@augustcellars.com>
> Cc: Christian M. Amsüss <christian@amsuess.com>om>; core@ietf.org WG
> <core@ietf.org>
> Subject: Re: [core] Modernized Link Format
> 
> Jim Schaad wrote:
> > Would it be possible to get a link to CoRAL as I don't think I have ever seen
> it.
> 
> https://tools.ietf.org/html/draft-hartke-t2trg-coral-05
> 
> Klaus