Add SAP Business Partner example for the ontology layer

[marioapiphani]

examples/ has one ontology-layer example today (flights.yaml). This adds a second, drawn from an enterprise ERP domain, that exercises ontology constructs the existing example does not reach:

• entity subtyping — Customer declares extends: [ BusinessPartner ]; flights.yaml has no EntityType subtyping
• a derived population — Customer uses concept-level derived_by to define its population as exactly those business partners carrying a customer number, rather than asserting it. flights.yaml uses derived_by only on relationships, for derived attributes.
• four-part compound identity — CustomerSalesArea is identified by customer + sales organization + distribution channel + division. The existing example tops out at two parts.

It also covers ground shared with flights.yaml — value types with requires, associations with and without functional multiplicity, verbalizations in both reading directions, and ontology_mappings down to a logical model — so it stands alone as a reading example.

Source-system provenance (SAP Data Dictionary domains and check tables) is recorded in the descriptions, showing one way to keep technical origin alongside a business-level model.

The README's examples/ entry is updated to name both ontology-layer models.

The file validates against ontology/ontology.json as shipped, with core-spec/osi-schema.json registered to resolve the remote $ref from the checkout:

import json, re, yaml
from jsonschema import Draft202012Validator
from referencing import Registry, Resource
onto = open("ontology/ontology.json").read()
core = Resource.from_contents(json.load(open("core-spec/osi-schema.json")))
reg = Registry().with_resources([(u, core) for u in set(re.findall(r'"\$ref": "(https://[^"#]+)', onto))])
v = Draft202012Validator(json.loads(onto), registry=reg)
print(sorted(v.iter_errors(yaml.safe_load(open("examples/sap_business_partner_ontology.yaml"))), key=lambda e: list(e.path)) or "VALID")

Prints VALID. No code changes.

🤖 Generated with Claude Code