Proposal: ThoughtSpot converter (bidirectional, TML ↔ Ossie)

[djwaldo]

ThoughtSpot would like to contribute a converter between ThoughtSpot's semantic model format (Model TML + Table TML, YAML) and the Ossie semantic model, following the established converter pattern.

Scope

• Bidirectional: tml_to_ossie (import) and ossie_to_tml (export)
• File-to-file, Python, mirroring the converters/databricks package shape (fixtures including a TPC-DS pair, roundtrip + property-based tests, per-converter CI workflow)
• custom_extensions with vendor_name: THOUGHTSPOT for lossless roundtrip of ThoughtSpot-only concepts; one row added to the well-known vendor examples table in core-spec/spec.md
• Mapping docs before code: a construct-mapping document and an expression/function-mapping document (each function in core-spec/expression_language.md classified as direct ThoughtSpot formula equivalent, requiring a SQL passthrough function, or unmappable → converter issue) will be posted on this issue for community review before the code PR

Proposed mapping sketch (high level)

Ossie	ThoughtSpot
datasets	Model model_tables + Table TML (physical source)
fields	table columns / ATTRIBUTE formulas
metrics	MEASURE columns / formulas
relationships	Model joins
ai_context	synonyms, Spotter instructions
custom_extensions[THOUGHTSPOT]	join types, aggregation defaults, formats, other ThoughtSpot-only metadata

Happy to adjust scope/shape based on feedback — the mapping documents will follow as comments on this issue.

— Damian Waldron (ThoughtSpot); damian.waldron@thoughtspot.com on the dev list.