Week 05 Report

Weekly Report - Week 5 (June 22 - June 28, 2026)

I performed the following tasks during week 5:

STAC transformation layer implementation (stac_transformer.py)

Implemented STAC transformation initially using pystac, then replaced it entirely with a pure dict-based approach after profiling. pystac's add_child and similar methods run internal catalog validation on every call, which on the Fraunhofer dataset (5,610 Things, 22,941 Datastreams) made a full transformation take close to five minutes end-to-end. Switching to direct dict construction dropped transformation time to sub-second for the same dataset.
The pure dict approach also provides tighter control over STAC 1.0 compliance than delegating to pystac's output shape. All link relations, datetime formatting, bbox derivation, and collection extent computation are implemented explicitly as per the STA-STAC-Mapping-Reference.md spec.
Implemented the full links system and datetime storage in a dedicated fix pass after identifying that the initial implementation was not producing STAC 1.0 compliant link structures in the catalog and collection responses.
Datastreams with no usable phenomenon_time are skipped with a warning since a STAC Item without datetime is invalid. Things where all Datastreams are skipped produce Collections with no Items and are logged accordingly.

Caching layer implementation (cache.py)

Implemented write_stac_catalog which flattens the transformer output into Redis keys following the stac:catalog, stac:collection:{id}, and stac:item:{collection_id}:{id} structure. Old keys are purged via SCAN before the new set is written to prevent orphaned data from previous cycles.
Discovered that istSOS4 already maintains a synchronous Redis client at app.db.redis_db. The caching layer imports and uses this connection directly, following the sta2rest pattern already established in the codebase, rather than opening a second connection.
File-based caching was prototyped first and discarded. Redis is the confirmed and currently operating architecture. Redis RDB persistence is confirmed to be working. Logs show the background save completing after the first cycle, writing over 10,000 changes in under 60 seconds.

API layer (api.py)

Implemented the connector API router with /connector, /connector/stac, and the collection and item endpoints, included in the main FastAPI application. All endpoints are live and returning STAC 1.0 compliant responses.
GET /connector/stac/collections on the Fraunhofer dataset returns approximately 11.3 MB of STAC-compliant data, which is expected from 5,610 Things and 22,941 Datastreams. The response is correct, but slow at this payload size. Pagination and scalability improvements are scoped for after the midterm evaluation or the final polishing weeks.

End-to-end validation

The full STAC output was validated against Radiant Earth's STAC Browser, which rendered the catalog, collections, and items correctly and confirmed STAC 1.0 compliance end-to-end.

Details can be found in:

What do I plan to do next week?

Implement the testing infrastructure before the midterm evaluation to hit the midterm deliverable. This is the priority for week 6.
dcat_transformer.py implementation begins week 7 onwards, following the STA-DCAT-AP-Transformation-Layer-Reference.md spec authored in week 3. The scheduler already calls build_dcat_catalog and writes DCAT cache independently of STAC, so the implementation slot is ready.

Am I blocked on anything?

No blockages. The STAC pipeline is running end-to-end and serving validated responses.