README.md

---
license: cc-by-4.0
language:
  - en
pretty_name: Ballast T2
size_categories:
  - 10K<n<100K
task_categories:
  - text-retrieval
tags:
  - knowledge-base
  - textbooks
  - openstax
  - rag
  - grounding
configs:
  - config_name: passages
    data_files: "passages/tier=T2/lang=en/lic=by/rank_bucket=*/*.parquet"
  - config_name: sources
    data_files: "sources.parquet"
---

# ⚓ Ballast T2

The textbook tier of the Ballast knowledge artifact: **61 OpenStax
textbooks as passage chunks**, 90,445 chunks across 9,018 linked
sections (≈92 MB of text, 34 MB zstd parquet). Where
[T0](https://huggingface.co/datasets/OpenBallast/ballast-t0) carries facts
as triples and [T1](https://huggingface.co/datasets/OpenBallast/ballast-t1)
carries encyclopedia prose, T2 carries pedagogical prose: definitions,
worked explanations, and method text of the kind reference corpora state
but never teach.

## Layout

```
passages/tier=T2/lang=en/lic=by/rank_bucket=7/part-0.parquet
sources.parquet        # one row per book: name, homepage, pinned git SHA, license
licenses.parquet       # license registry the per-chunk lic key resolves to
manifest.json          # per-file counts, bytes, sha256, build provenance
```

`passages` schema matches T1 (`qid`, `chunk_idx`, `title`, `heading`,
`text`; chunker `t1-chunk-v1`, ~1.2 KB atomic chunks). Two T1 conventions
do **not** apply here: T2 v1 has no notability ranking; every chunk sits
in the tail bucket (`rank_bucket=7`), so corpus levels are a no-op; and
chunks are keyed to book sections rather than Wikidata entities.

```sql
SELECT title, heading, text
FROM read_parquet('ballast-t2/passages/**/*.parquet', hive_partitioning=true)
WHERE text ILIKE '%standard deviation%' LIMIT 5;
```

## Run it locally (serving format)

`serving/sqlite/` carries the same chunks as a single-level SQLite corpus
for the [`ballast` CLI](https://github.com/OpenBallast/ballast-cli)
(v0.3.0+): 25 MB download, 116 MB on disk. Documents are the 9,018 book
modules; the name index is module titles plus per-module index terms, so
lookup resolves questions like "what is marginal cost" to the right
chapter. Entity-name lookup over textbook prose is functional but
unbenchmarked.

```bash
uvx openballast pull --tier t2
uvx openballast serve --corpus t2     # proxy :11435 + MCP :11436
```

Serving ids are corpus-local (`D…`); provenance stays in this parquet
distribution (`chunk_id`, pinned `revision`, `source_url` per chunk).

## Provenance: pinned against a license flip

Every book is ingested from its official OpenStax source repository at a
**pinned git commit**, recorded per book in `sources.parquet`
(`access_path` = `git:<repo>@<sha>`, retrieved 2026-08-02). The pinning is
load-bearing: parts of the OpenStax catalog moved from CC BY to
CC BY-NC-SA in spring 2026, and aggregator license metadata did not always
track the change. This distribution therefore trusts **only the license
text at the pinned commit of the official repo**, never catalog metadata.

The research build behind this artifact contains a second cell: 9
post-flip titles (10,050 chunks) under **CC BY-NC-SA 4.0**. That cell is
**excluded from this distribution** to keep the published artifact
commercially safe under a single license. The full manifest documents both
cells, so the exclusion is visible rather than silent.

## Curation & processing

What was selected, what was done to it, and why, so this is auditable
rather than "some textbook text":

1. **Selection.** The OpenStax catalog, and nothing else: every book with
   an official source repository under `github.com/openstax` at retrieval
   time (2026-08-02). No aggregators, no mirrors, no PDF scrapes: the
   official CNXML/collection source is the only ingestion path, because it
   is the only place license status is authoritative.
2. **Pinning.** Each repository is pinned to one commit
   (`sources.parquet.access_path`), chosen as the newest commit whose
   `LICENSE` grants CC BY 4.0. Books whose current license is
   CC BY-NC-SA are carried at their NC state, not silently rolled back;
   that cell is excluded from this distribution (see Provenance).
3. **License resolution.** Per-book license read from the repo's license
   file at the pinned commit under versioned rules
   (`t1-license-rules-v2`), never from catalog or aggregator metadata:
   the spring-2026 relicensing showed the metadata lags the repos.
4. **Extraction & chunking.** Book markup to plain prose with the same
   deliberately simple parser as T1 (`t1-chunk-v1`): boilerplate sections
   dropped, figures and math markup dropped, paragraphs merged greedily
   to a ≈1.2 KB atomic-chunk target, section heading carried per chunk.
5. **Dedup.** Exact-duplicate chunks removed within the tier
   (`dedup_ledger.parquet` records what, if anything, was suppressed:
   zero for this build).
6. **Why this tier exists.** The companion tiers carry facts (T0) and
   encyclopedia prose (T1). Pedagogical prose is a different knowledge
   shape (definitions and worked method text), and keeping it a separate,
   separately-licensed tier lets downstream users include or exclude it
   deliberately rather than inheriting it mixed in.

## Limitations

- **Pedagogical prose, verbatim.** Exercises, figure references, and
  chapter cross-references survive in chunk text; figures themselves and
  math markup are dropped by the parser (`t1-chunk-v1`, the same
  deliberately simple parser as T1, with the same class of markup residue).
- **No notability ranking** (see above): download is all-or-nothing at
  34 MB, which at this size is not a hardship.
- **English only, one catalog.** T2 v1 is OpenStax-only; the tier is
  designed to grow by adding pinned sources, not by re-crawling.

## License & attribution

**CC BY 4.0** (OpenStax, Rice University). Attribution resolves through
each chunk's partition and `title` to the book row in `sources.parquet`,
which carries the book's name, homepage, and pinned source commit.
OpenStax is not affiliated with and does not endorse this distribution.

Companion artifacts:
[ballast-t0](https://huggingface.co/datasets/OpenBallast/ballast-t0),
[ballast-t1](https://huggingface.co/datasets/OpenBallast/ballast-t1),
[ballast-evalsets](https://huggingface.co/datasets/OpenBallast/ballast-evalsets).

Questions and issues: [github.com/OpenBallast/ballast/issues](https://github.com/OpenBallast/ballast/issues).