Is the Service Hub an Solid App/Pod ?

[phochste]

As discussed in the 2021-11-23 meeting, there was a discussion if a Service Hub should be defined as a Solid App (a client that can talk the Solid protocol), or a Solid Pod in a more extreme case.

This is for me not clear why this is an immediate requirement, rather than that we must prove that it can't be anything else than a Solid App/Pod. The jury is still out.

As far as the experiment and the thinking goes in the current form:

Notifications

• The Service Hub must be an LDN Receiver (for incoming notifications)
• The Service Hub must be an LDN Sender (for outgoing notifications)
• The Service Hub has no requirements to read other LDN inboxes (not a Consumer)

Event log

• The Service Hub must have an Artefact Event Log implementation (where the protocol requirements still need to be discussed).

Artefacts

• Extra requirements on the artefacts due to the protocols used?

[RubenVerborgh]

Not having been part of the discussion, I just want to highlight this seems to be a false dichotomy. Something can be both an app/client and a Pod.

i.e., "client" is a role rather than an absolute entity, as is the case with HTTP and in particular proxies: https://rubenverborgh.github.io/WebFundamentals/architecture/#client-server-relative

[phochste]

Indeed it is a false dichotomy. What I meant was that the defining a Service Hub as a Solid App was too vague what this means for implementers of a Service Hub in the context of the Mellon/Erfgoed proposed service model.

What roles should the Service Hub play is indeed a better question.

[mielvds]

It's not vague in the sense that you're demanding all Service Hubs to be able to read (and write) data to a Solid Data Pod. The burden of defining this is with the Solid people like @RubenVerborgh. But I agree that this probably entails more than what's strictly necessary. Finding out the requirements is a good idea.

That said, a Service Hub implementer needs to know what to comply to, so not defining it as a Solid App or LDP Client puts the burden on us to specify exactly what it should or should not be able to do. Listing roles is informative, but it's not enough.