add support for schema.org

[tomkralidis]

Fixes #231. Also adds early out for autodetection (first schema found).

[pvgenuchten]

Nice work Tom,

Write support

i get impression you didn't check your implementation on https://validator.schema.org/, because it still has quite some validation issues, see below.

currently dataset type is not detected in https://validator.schema.org/
when using the validator, make sure to embed json in

<script type="application/ld+json">{}</script>

I wonder if we should use some of this work inside pycsw/pygeoapi...

noticed this on distribution

should be @type:'schema:dataDownload'
format or encoding can be used for the mimetype
seems the validator assumes 'type': as '@type'

Read support

I notice you also added read support, i tried with

pygeometa metadata import schema-org.json --schema schema-org -v DEBUG

and got a

WARNING:pygeometa.core:Import failed: list indices must be integers or slices, not str
null
...

when debugging

from pygeometa.schemas.schema_org import SchemaOrgOutputSchema
sos = SchemaOrgOutputSchema()
f = open("./schema-org.json", "r")
f2 = sos.import_(f.read())

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/geopython/lib/python3.10/site-packages/pygeometa-0.17.dev1-py3.10.egg/pygeometa/schemas/schema_org/__init__.py", line 116, in import_
    geo = md['spatialCoverage']['geo']
TypeError: list indices must be integers or slices, not str

would be nice this if this error is reported by the command-line client
schema-org.zip

The interesting part here is that rdf typically allows a single or a list of items as content of an element, which brings us to a next topic, seems this implementation expects a json-ld serialisation of rdf, which indeed is the most common form of schema-org. However quite some implementations of schema-org use RDF-a/microdata. In theory one can also serialise schema.org as turtle or rdf/xml. To support that case, rdflib can be used to read the rdf and serialise it to json-ld, before parsing.

after fixing the spatialcoverage, next error:

  File "/geopython/lib/python3.10/site-packages/pygeometa-0.17.dev1-py3.10.egg/pygeometa/schemas/schema_org/__init__.py", line 123, in import_
    mcf['spatial']['datatype'] = 'vector'
KeyError: 'spatial'

seems the datatype is set before spatial is initialized

[jmckenna]

seconded, good work, but testing through https://validator.schema.org/ is critical (I wish there was an API available to validate, instead of manually testing through the validator).

[pvgenuchten]

Validator is not available as a service, but a shacl oriented test is available at https://github.com/google/schemarama/blob/main/core/test/shacl-test.js

[tomkralidis]

@jmckenna @pvgenuchten I dusted off this PR and pushed some updates:

import: successful import from schema-org/JSON-LD (sample) to MCF, as well as examples (thanks @pvgenuchten) in:

• https://data.overheid.nl/dataset/31047-bevolking--hoogstbehaald-onderwijsniveau-en-onderwijsrichting
• https://nationaalgeoregister.nl/geonetwork/srv/api/records/32422e58-90ff-47b5-be0a-d1221bf96664
• https://search.dataone.org/view/doi%3A10.60635%2FC3PP5X

export: successful export of sample.yml and validated against https://validator.schema.org/ (0 errors, 0 warnings).