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Web of Things (WoT) Binding Templates
http://w3c.github.io/wot-binding-templates/
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Indicating MQTT version in TDs #174

Open egekorkan opened 1 year ago

egekorkan commented 1 year ago

Currently, the MQTT binding does not specify which version to be used. I think we should be able to describe that and also give a default value in case it is not specified.

I propose:

egekorkan commented 1 year ago

What do you think @relu91 ?

JKRhb commented 1 year ago

Thank you, @egekorkan, I was actually about to open a similar issue :)

relu91 commented 1 year ago

What do you think @relu91 ?

I thought of introducing that element when I worked on the ontology revamp. However, I did not introduce it because the whole ontology was tailored to version 3.1.1. Moreover, I questioned myself if it made sense to have a version tag OR two different ontologies to describe the different protocol features. The problem with two different ontologies is that we are going to have some duplicated terms... but it solves the versioning issue nicely. I don't have a clear answer yet but I am eager to know what you think about these two possible approaches.

egekorkan commented 1 year ago

As far as I have understood, an MQTT 5.0 broker would not have an issue if an MQTT 3.1.1 client connects to it so the additional features would not be breaking change. If this is indeed possible. More importantly, given that we would use the same URI scheme for 3.1.1. or 5.0 even if we have different ontologies, we would need a way to indicate the version I think.

JKRhb commented 1 year ago

I'd also be in favor of adding a mqv:version field, as, for example, in the Dart ecosystem you have two different implementations for MQTT 3 and MQTT 5. So being able to differentiate between the two versions would be very nice. Would it be possible to define the version "globally" by the way, i.e., for the whole TD? Or do you need to provide an override of the default for each form?

Furthermore, should it also be possible to also indicate MQTT version 3.1 (besides version 3.1.1)?

relu91 commented 1 year ago

More importantly, given that we would use the same URI scheme for 3.1.1. or 5.0 even if we have different ontologies, we would need a way to indicate the version I think.

I was actually thinking to use two different URI schemes pointing to two different ontologies. It would solve this:

Would it be possible to define the version "globally" by the way,

But I mostly agree with you that is overkill.

danielpeintner commented 5 months ago

Based on the the different MQTT versions available on various platforms it might make sense to be able to indicate the version used.

Anyhow, based on the claim that

MQTT 5 is designed to be backwards compatible with MQTT 3.1.1 to some extent

I am not sure if is really a use-case per se. I see it more as "nice to have".