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The semantic layer is the unit of analysis output. Every dataset has a history of semantic-layer versions; the UI always reads the latest one. When people on the team say “the analysis,” they mean a semantic-layer version.

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What’s in a version

A version is built from per-component artifacts. Each component (column stats, EBM model, EBM graphs, UMAP, etc.) writes its own outputs and registers them in a single manifest.json. The pieces that the UI most directly consumes: Surprise finding writes its top-N output directly to the summand-task-outputs DynamoDB table — not to S3 — so the Insights tab reads from there. Predictions for new rows are produced on-demand by re-loading the model; there’s no per-row predictions Parquet sitting around. All S3 artifacts are stored under a versioned path (s3://summand-artifacts/curated/{connectorId}/{datasetId}/{version}/) so older versions remain readable.

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Why a semantic layer

Every part of the UI — and the Summand assistant — needs to answer questions like “What’s the mean of revenue by segment?” or “Which features matter most?” without re-querying the source. The semantic layer is the cached, structured answer to those questions. Concretely:
  • Summand gets grounding facts from the semantic layer instead of hallucinating numbers.
  • Charts suggested by Summand reference real columns and aggregations from the layer.
  • Refresh comparisons become straightforward — diff version N against version N–1.

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Versioning model

A version is (datasetId, version_number). Versions are append-only and immutable: once written, an artifact stays put. Updating the dataset (re-upload, refresh, target change) creates a new version; it does not mutate the previous one.

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Time travel

The Overview tab shows the latest version by default. Power users on Enterprise plans can pin an older version for comparison — useful for tracking how a model’s understanding of the data has shifted over months.

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Storage and retention

Semantic-layer versions count toward dataset retention, not toward tier-based dataset caps. Pro and Enterprise retain all versions for the life of the subscription. Free tier retains only the latest two versions per dataset.

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Relationship to data warehousing

The semantic layer is not a metrics store like Cube or LookML. It’s narrower:
  • It describes a single dataset, not a curated cross-source business model.
  • It’s generated, not authored — you don’t write .yml to maintain it.
  • It exists to power Summand’s analysis surface; it doesn’t expose itself as a SQL endpoint.
If you need a metrics layer, Summand pairs naturally with one — point both at the same warehouse — but the semantic layer described here is internal to a dataset.