[LAD] Programming LV2 plugin from scratch tutorial video series

[Robin Gareus]

On 10/18/21 10:54 PM, Fons Adriaensen wrote:

> I never got to grips with turtle. 

https://www.w3.org/TR/turtle/ to the rescue :)

There is currently ongoing work to allow JSON-LD as alternative, but
that's just the encoding.

> In particular not with things like:

> @prefix doap:  <http://usefulinc.com/ns/doap#> .
> @prefix lv2:   <http://lv2plug.in/ns/lv2core#> .
> @prefix rdf:   <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfs:  <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix units: <http://lv2plug.in/ns/extensions/units#> .
> 
> All docs and tutorials I found mention that the URLs do NOT
> mean that an application reading a file that contains them
> would actually need to read them from the web (which would
> be a unacceptable security risk anyway).

URIs are just used as unique identifiers. They do not even need to
resolve and one can use urn: as well. However in most cases they point
to online documentation which is helpful to developers.

> Which raises the question why those @prefix lines are 
> required at all. 

@prefix just syntactic sugar, so you do not have to spell out the full
URI every time. Instead of e.g.
  http://lv2plug.in/ns/lv2core#ControlPort
you can just write
  lv2:ControlPort

> So all that these lines seem to provide is some illusion
> of conformity which isn't enforced or checked at all. 

Those URIs are defined in header files of the LV2 ontology and must
match, otherwise a LV2 plugin does not conform to the spec. There are
tools like lv2lint to check the validity, but other than that, they are
just unique IDs.

> So the conclusion is that this isn't any better than any
> ad-hoc way of encoding the plugin metadata.

Except it is not ad-hoc, but a w3c standard. Why invent an new meta-data
schema for unique resource IDs, when there is already a very good one
out there, that is also formalized as RFC?

As side-effect you can also use existing tools from the semantic web to
index and search LV2 plugins. IIRC the MOD website uses that.

I hope that clarifies things,
robin


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