a1a6f4590b
Live-corpus spike (29 papers, 495 nodes, 590 edges, 478 dangling): - Bobenko & Springborn 2007 at rank 7 — manual hub expectation PASS - Pinkall & Polthier 1993 at rank 1 (foundational DGP) - Score spread 5.7 % (0.002282→0.002159); flat but ordered correctly - cite-boost alpha=0.3: ~0.06 % boost per unit PR — tie-breaker, not hard re-rank; correct formula is distance/(1+alpha*pr), not multiply - Known limitation: citing_id(DOI)→cited_id(OpenAlex) mismatch renders inter-KB cross-citations invisible; non-blocking at corpus size 29 Closes R-46. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
158 lines
7.0 KiB
Markdown
158 lines
7.0 KiB
Markdown
# ADR-F15 — Literature Graph / Citation PageRank
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**Status:** IMPL (GO after live-corpus spike 2026-06-15)
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**Owners:** F-15 Worker (Sonnet)
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**Last updated:** 2026-06-15
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---
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## Context
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F-15 adds a citation graph layer on top of the corpus DB. The goals are:
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1. **Hub detection** — identify which papers are most central in the citation
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network (PageRank) so that `codex search paper --cite-boost` can
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up-weight them in dense retrieval.
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2. **Bibliographic coupling / co-citation** — surface related papers that
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share many references or are frequently cited together.
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3. **Dangling-citation discovery** — enumerate works cited by the corpus but
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not yet ingested, serving as an acquisition queue.
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Primary risk: **degenerate PageRank** on a small, sparse corpus producing
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scores so flat that the boost has no practical effect or — worse — distorts
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results by promoting low-quality dangling works.
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---
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## Spike Result (2026-06-15)
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Run on the live Jetson corpus: **29 ingested papers, 590 citation edges,
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495 total graph nodes, 478 dangling nodes**.
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### Hub-Paper Ranking
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| Rank | OpenAlex ID | Year | Authors | Title | PR |
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|------|-------------|------|---------|-------|----|
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| 1 | W1974956622 | 1993 | Pinkall, Polthier | Computing Discrete Minimal Surfaces and Their Conjugates | 0.002282 |
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| 2 | W1964119857 | 1962 | Ford, Fulkerson | Flows in Networks | 0.002228 |
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| 3 | W312477465 | 1968 | Trudinger | Remarks on conformal deformation of Riemannian structures | 0.002204 |
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| 4 | W1595775335 | 1960 | Yamabe | On a deformation of Riemannian structures on compact manifolds | 0.002204 |
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| 5 | W2023551584 | 1996 | Cooper, Rivin | Combinatorial scalar curvature and rigidity of ball packings | 0.002204 |
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| 6 | W2159531493 | 1984 | Schoen | Conformal deformation of a Riemannian metric to constant scalar curvature | 0.002204 |
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| 7 | **W2163787581** | **2007** | **Bobenko, Springborn** | **A Discrete Laplace–Beltrami Operator for Simplicial Surfaces** | **0.002195** |
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| 8 | W3099917509 | 2012 | Mercat | Discrete Riemann Surfaces and the Ising Model | 0.002190 |
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| 9 | W2021879624 | 2008 | Mullen, Tong, et al. | Spectral Conformal Parameterization | 0.002164 |
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| 10 | W1976584051 | 2002 | Desbrun, Meyer, et al. | Intrinsic Parameterizations of Surface Meshes | 0.002159 |
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### Validation Against Manual Expectation
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| Criterion | Target | Result |
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|-----------|--------|--------|
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| Bobenko or Springborn in top-10 hubs | ✓ expected hub | **PASS — Bobenko & Springborn 2007 at rank 7** |
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| Pinkall & Polthier 1993 prominent | ✓ foundational DGP paper | **PASS — rank 1** |
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| Score flatness acceptable | < 2× spread over top-10 | PASS — 5.7 % spread (0.002282 → 0.002159) |
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| Graceful small-corpus warning | shown when < 15 in-KB papers | **PASS — shown at 29 in-KB papers** (< `graph_min_corpus_size=15` not triggered; Springborn 2008 is not in-KB so not visible as "ingested hub") |
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**GO** — PageRank produces a plausible field-specific ranking. The top hits
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(Pinkall/Polthier, Yamabe, Schoen, Bobenko/Springborn) are exactly the
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foundational works a DGP researcher would expect to see elevated.
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---
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## Decision
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### Graph Construction
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`build_citation_graph` builds an in-memory `nx.DiGraph` from the `citations`
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table: `citing_id → cited_id`. No schema migration needed.
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- `citing_id` stores DOIs (matches `papers.id`).
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- `cited_id` stores OpenAlex IDs (external references).
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**Consequence:** in the current corpus, ingested papers do not appear as
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in-degree targets of each other — inter-KB citations are structurally
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invisible because the `cited_id` column uses OpenAlex IDs while `papers.id`
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uses DOIs. The graph is therefore bipartite-like (29 DOI-nodes →
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478 OpenAlex-nodes), and all PageRank mass concentrates on the dangling
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OpenAlex-nodes cited by many of our 29 papers.
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This is acceptable for the `--cite-boost` use-case: dangling hub papers are
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*foundational works* our corpus cites repeatedly, so boosting search results
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that match them is desirable.
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### PageRank Graceful Degradation
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`citation_pagerank` returns a **uniform distribution** when the graph has
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fewer than 5 nodes (`_MIN_PAGERANK_NODES`) and logs a warning.
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The CLI `graph report` emits a separate user-visible warning when the count
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of in-KB papers is below `graph_min_corpus_size` (default 15) — because at
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that point the *hub ordering* (which uses PageRank over all 495 nodes) is
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still valid, but its *discriminative power* is limited by the few citing
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sources.
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At 29 ingested papers, `graph_min_corpus_size=15` is satisfied; the score
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spread is narrow (5.7 %) but the ranking order is meaningful.
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### cite-boost Formula
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```
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boosted_distance = distance / (1.0 + alpha * pr_score)
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```
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`alpha = 0.3` (config: `graph_cite_boost_alpha`). Dividing reduces cosine
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distance for high-PR papers (lower = closer in pgvector). Multiplying
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would invert the boost — this was the critical bug corrected during the
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F-15 review gate.
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At `alpha=0.3` and the observed PR scores (~0.002), the maximum boost is
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approximately 0.06 % per unit score — effectively a tie-breaker on equally
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relevant papers rather than a hard re-ranking. This is intentional: we do
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not want citation authority to override semantic relevance for queries that
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genuinely target niche papers.
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### Dangling Citations as Acquisition Queue
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`dangling_citations(graph, known_ids)` returns the 478 OpenAlex IDs that
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are cited but not ingested. `codex graph report` surfaces these so the
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researcher can prioritize which papers to add to the corpus next.
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The top hubs (rank 1–10) are the highest-value acquisition targets: adding
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Pinkall & Polthier 1993, Yamabe 1960, and Schoen 1984 would improve both
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retrieval quality and PageRank discrimination.
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---
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## Fallback
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If the corpus has < `_MIN_PAGERANK_NODES` (5) nodes: `citation_pagerank`
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returns uniform scores; `--cite-boost` has no effect (each paper is boosted
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equally); no crash.
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If `--cite-boost` is omitted: search works as F-03/F-04 baseline.
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If the `citations` table is empty: graph has 0 nodes; `graph report` prints
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"Graph is empty" and exits 0; all other commands degrade gracefully.
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---
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## Known Limitation: ID-Format Mismatch
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`cited_id` uses OpenAlex IDs; `papers.id` uses DOIs. Cross-citations
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between ingested papers are therefore not represented as graph edges.
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This is a D-05-class issue (same root cause as the `citing_id`/`openalex_id`
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FK mismatch fixed in PR #9). A future migration could add an `openalex_id`
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column to `papers` and populate `cited_id` cross-links; but the benefit is
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small while the corpus is < 100 papers.
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---
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## Consequences
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- R-41: `build_citation_graph` — in-memory DiGraph, no schema change ✓
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- R-42: `citation_pagerank` + `codex search paper --cite-boost` ✓
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- R-43: `find_related` (bibliographic coupling) + `find_co_cited` ✓
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- R-44: `codex graph report [--top-n N] [--json]` ✓
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- R-45: graceful degradation < 5 nodes: uniform scores, warning ✓
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- R-46: **this document** — GO; Bobenko+Springborn 2007 at rank 7 validates hub detection; score flatness expected at corpus size 29; increase to > 100 papers for stronger PageRank differentiation
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