# Synthesis — the shard spectrum: one capability model across nine systems

Date: 2026-06-14
Source kind: **synthesis** — consolidates the engine and tool deep dives plus the two
Nelson conceptual systems into a single comparative model that feeds the **shard adapter
contract** (`SHARD-WP-0002` T11–T16)
Lens: shard-wiki — what a backend must expose to participate, expressed as *spectra* of
capability rather than a yes/no checklist

> Purpose. Nine systems have been studied: two conceptual ancestors (**Xanadu**,
> **ZigZag**), four engines (**XWiki, TWiki, Foswiki**, + the wiki-engines landscape),
> and three modern tools (**Roam, Obsidian, Notion**), against the federation and
> origin research (federation-concepts, c2, yawex). They were studied one at a time;
> this document reads them *across* each other. The payoff is a small set of
> **capability spectra** — addressing, structure, history, query, translation,
> attachment mode, operational envelope, access grant — each anchored at both ends by a
> real system. That spectrum *is* the adapter contract's design surface. It also folds
> the post-engine use cases (**UC-44–UC-59**) into the existing `SHARD-WP-0002` tasks.

Inputs: `research/260608-federation-concepts`, `research/260608-wikiengines-overview`,
`research/260613-{xwiki,twiki,foswiki}-deep-dive`,
`research/260614-{xanadu,zigzag,roam,obsidian,notion}-deep-dive`. Output target:
`spec/TechnicalSpecificationDocument.md` (adapter contract) via `SHARD-WP-0002`.

---

## 1. The shard family matrix

Candidate-shard backends across the dimensions that matter to the contract. (Xanadu and
ZigZag are *not* shards — they are the conceptual ideals each column aspires to; listed
last as reference anchors.)

| Backend | Substrate | Attach mode | Addressing | Structure | History | Native query | Transclusion | →Markdown | Write granularity |
|---------|-----------|-------------|-----------|-----------|---------|--------------|-------------|-----------|-------------------|
| **Git folder / repo** | files | file-store | path (+ commit) | flat MD + frontmatter | **git-native** | no | no | native | per-file |
| **Obsidian vault** | files | file-store **or** in-app plugin | path + **in-file `^id`** | frontmatter (in-file) | none (Git plugin) | plugin (Dataview) | in-file `![[ ]]` | native (OFM) | per-file |
| **TWiki** | files + RCS | file-store / API | path | `%META%` in-file | **open file (RCS)** | no | include macro | lossless (TML) | per-topic |
| **Foswiki** | pluggable store | file-store / API | path | `%META%` in-file, N records | open file / PlainFile | no | include macro | lossless (TML) | per-topic |
| **XWiki** | DB (Hibernate) | in-engine host / REST | path | **XObjects/XClass** | internal (`xwikircs`) | yes (XWQL) | macro | engine syntax | per-page / per-object |
| **Roam** | client DataScript | **in-app host only** | **store UUID** | `key::` attrs | internal (txn log) | **yes (Datalog)** | **block embed** | (Roam MD) | **per-block** |
| **Notion** | hosted Postgres | **external API only** | **store UUID** | **DB schema + relations + rollups** | internal, not portable | **yes (DB query)** | synced block | **lossy** | **per-block** |
| **TiddlyWiki** | single file | file-store | path | typed tiddlers | none | no | transclusion | varies | **whole-file** |
| **MediaWiki / Confluence** | DB | API | path | wikitext / macros | internal-only | limited | templates | lossy | per-page |
| — *Xanadu (ideal)* | permascroll | — | **tumbler (span)** | spans + links | permanent | — | **content-identity** | — | span |
| — *ZigZag (ideal)* | cells/dims | — | cell id | **N dimensions** | — | dimension walk | clone | — | cell |

Reading the matrix top to bottom is reading shard-wiki's difficulty gradient: **Git
folder → Obsidian** are the friction-free, INTENT-native cases; **TWiki/Foswiki** add
syntax translation but stay file/diffable; **XWiki/Roam/Notion** add DB structure, store
addressing, and (for Roam/Notion) non-file substrates; **Notion** is the hardest
(closed, hosted, lossy, rate-limited). Xanadu/ZigZag mark where the *ideals* live.

---

## 2. The capability spectra (the contract's real shape)

Each capability is **not boolean** — it is a position on a spectrum with a real anchor at
each end. This is the core synthesis claim: the adapter contract should model *positions*,
and federation operations should degrade by position.

1. **Addressing granularity** — `none → whole-page(path) → in-file span(Obsidian ^id) →
   store-minted span(Roam/Notion UUID) → portable tumbler(Xanadu ideal)`. (UC-51, UC-44/45.)
2. **Content identity** — `none → path/title match → content fingerprint(hash) →
   span-set/equivalence(Xanadu)`. Drives equivalence + reverse-transclusion. (UC-46, UC-27.)
3. **Structure** — `flat Markdown → in-file frontmatter → in-file %META% → DB
   objects(XWiki) → DB schema+relations+rollups(Notion)`. The git-diffable forms federate
   easily; DB-locked forms need sidecar + fidelity reporting. (UC-34, UC-39, UC-58.)
4. **History** — `none → internal-only/not-portable(Notion/Confluence) → open file
   format(TWiki RCS) → git-native(Git/Obsidian-with-Git)`. Internal ⇒ *supplement*;
   open-file ⇒ *import*; git-native ⇒ *adopt*. (UC-36, UC-41.)
5. **Native query** — `none → text search → datalog(Roam) → DB query(Notion/XWiki)`.
   Where present, **delegate** derived-view computation; else compute over the projection.
   (UC-52, UC-05, UC-54.)
6. **Translation to Markdown** — `native → lossless round-trip(Foswiki TML↔HTML) →
   lossy-with-fidelity-report(Notion)`. Lossless ⇒ writable; lossy ⇒ read/projection floor
   + visible fidelity loss. (UC-42, UC-59, UC-03.)
7. **Attachment mode** — `file-store direct(Obsidian/TWiki) → in-engine hosted
   adapter(Roam/XWiki) → external-API only(Notion)`. A backend may offer **more than one**
   (Obsidian offers both; TWiki file-or-API). (UC-40, UC-38, UC-50, UC-57.)
8. **Operational envelope** — `local/unbounded → rate-limited+eventually-consistent+
   paginated(Notion ~3 rps)`. Determines whether projection can be live or must be
   cache/poll/webhook. (UC-57, UC-31.)
9. **Access grant** — `open(L0) → token → OAuth scoped + revocable(Notion)`. The backend
   may *enforce* no-silent-mutation (Notion scoped grants). Ties the authz-in-core ladder.
   (UC-57, [[shard-wiki-auth-in-core-decision]].)
10. **Write granularity** — `whole-file(TiddlyWiki) → per-page(Git/Obsidian/TWiki) →
    per-block(Roam/Notion)`. Sets overlay/patch/lock/conflict scope. (UC-35.)
11. **Content types** — `Markdown-only → typed records(XWiki/Notion DB) → non-Markdown
    assets(Excalidraw/Canvas/attachments)`. The page model must stretch to all three.
    (UC-55, UC-58.)

Design consequence: **T11's capability vocabulary should be these eleven spectra**, not
the original flat `read/write/diff/...` list. The flat verbs remain as the *operations*;
the spectra are the *profile* that says how well each verb is supported and how it
degrades.

---

## 3. Cross-cutting findings (the through-lines)

- **Files-canonical, index-derived is the winning architecture.** Obsidian's
  MetadataCache, Git's working tree, and shard-wiki's own projection model all agree:
  the link graph / backlinks / structured index are **derived and rebuildable**, never a
  second source of truth. Roam/Notion invert this (DB canonical) and pay for it in
  portability. shard-wiki keeps files+journal canonical; everything else is projection.
  (Reinforces UC-05, UC-17–20; INTENT.)
- **Fine-grained addressing is real and adoptable** — Roam (`:block/uid`) and Notion
  (UUID) ship it store-minted; Obsidian ships it in-file (`^id`). The Xanadu tumbler is
  the unreached ideal (portable, transfinite). shard-wiki should **adopt native span IDs
  where present, fingerprint where not** (UC-51 + UC-46), and treat a portable span
  address as the open hard problem (Xanadu §11 Q1).
- **Transclusion ⇄ clone ⇄ embed is one primitive.** Xanadu transclusion, ZigZag clones,
  Roam block embeds, Obsidian `![[ ]]`, Notion synced blocks are the same idea at
  different fidelities. A single internal "reference-not-copy" primitive over an
  addressable union serves UC-32/44/45/51. (Convergence first noted in the ZigZag dive.)
- **Structure and history federate iff they live in text.** The sharpest recurring
  engine insight: `%META%`-in-file (TWiki/Foswiki) and frontmatter (Obsidian) diff and
  travel; XObjects and Notion DBs lock in. The contract should *prefer* in-text
  structure and *tolerate* DB structure via sidecar + fidelity report.
- **Three attachment modes, and a backend may span them.** The clean taxonomy
  (file-store / in-engine-host / external-API) plus the observation that one backend can
  offer several (Obsidian: file *or* plugin; TWiki: file *or* API) means **attach mode is
  a per-binding choice, capability-gated**, not a fixed property of the backend.
- **Notion proves the platform can enforce INTENT.** Scoped, revocable grants are
  no-silent-mutation made mechanical — evidence the principle is implementable, and a
  model for how shard-wiki represents partial/consented visibility.
- **The page model must stretch four ways at once:** prose Markdown, typed records
  (with N-per-page and inter-record relations), non-Markdown assets, and
  reference/query-defined pages. This is the heaviest single demand on T12.

---

## 4. How the post-engine use cases fold into the workplan

UC-44–UC-59 (from the five 260614 dives) map onto the existing adapter-contract tasks,
with one genuinely new thread needing a home (T16):

| UCs | Theme | Lands in |
|-----|-------|----------|
| UC-35, UC-50, UC-53, UC-57 | attachment mode + operational envelope + write granularity | **T11** (capabilities) + **T14** (binding) |
| UC-34, UC-39, UC-55, UC-58 | structured/typed payload, non-Markdown assets, DB schema+relations | **T12** (page model) |
| UC-36 | internal-only history (Notion) = supplement | **T13** (history) |
| UC-42, UC-59 | translation: lossless vs lossy-with-fidelity-report | **T15** (translation) |
| UC-31 | webhooks / push-vs-poll under eventual consistency | **T6** / **T11** envelope |
| UC-57 §6 | scoped, revocable grant; no silent mutation | **T11** access-grant + authz decision |
| **UC-44, UC-45, UC-46, UC-51** | span addressing, content identity, transclusion-as-reference | **T8** + **new T16** |
| **UC-47, UC-48, UC-52, UC-54** | dimensional navigation, query delegation, query-defined pages | **T5/T10** + **new T16** |

**New thread (T16): Addressing, content identity, and dimensional/query navigation.** No
existing task owns (a) the portable span-address scheme + content-identity model that
transclusion/overlay/reverse-lookup need, nor (b) the dimensional/query view model
(ZigZag dimensions, Roam/Notion query, Dataview query-defined pages). These are the
Nelson-ideals-meet-modern-tools thread and warrant their own design task.

---

## 5. Recommendations (decisions to record under SHARD-WP-0002)

1. **Model capabilities as the eleven spectra (§2), not flat verbs.** Keep verbs as
   operations; add the spectra as the profile. (T11.)
2. **Adopt native span IDs; fingerprint otherwise; keep portable-span-address open.**
   (T16, UC-51/46.)
3. **One reference-not-copy primitive** for transclusion/clone/embed over the addressable
   union. (T16/T8, UC-32/44/45.)
4. **Prefer in-text structure; tolerate DB structure via sidecar + fidelity report.**
   (T12/T15, UC-34/58/59.)
5. **Attach mode is a per-binding, capability-gated choice** across the three modes; a
   backend may offer several. (T14, UC-40/38/50/57.)
6. **Add operational-envelope and access-grant to the profile** as first-class fields.
   (T11, UC-57.)
7. **Delegate derived views to native query engines where present; else compute over the
   projection.** (T16/T5, UC-52/54.)
8. **Keep files + coordination journal canonical; all indexes/projections derived and
   rebuildable.** (Architecture invariant, INTENT.)

These honor INTENT: mechanism over policy (spectra not hard-coded behaviors), union
without erasure (fidelity reporting makes loss visible), graceful degradation (every
capability has a read/projection floor), no silent mutation (access-grant + overlay),
shard sovereignty (no backend forced to change substrate), Markdown-first/backend-neutral
(in-text preferred, DB tolerated).

---

## 6. Open questions escalated by the synthesis

1. **Portable span address** — still unsolved across heterogeneous backends (Xanadu's
   unbuilt part). Wrap native IDs in a shard-scoped address? (T16.)
2. **External-API write-through at scale** — is Notion-class write viable under ~3 rps,
   or read/projection/overlay/backup by default? (T14, UC-57.)
3. **Inter-record relations in the union** (UC-58) — typed links in the link graph, a
   separate relation index (ZigZag many-to-many), or both? (T16/T5.)
4. **Page model breadth** — can one model carry prose + typed records + non-Markdown
   assets + query-defined pages without becoming incoherent? (T12.)
5. **Dimensional navigation surface** — public API/UI paradigm or internal organizing
   concept? (T16, UC-47/48.)

---

## 7. Sources

This is a synthesis; primary sources are the nine dives' `findings.md` files plus
`research/260608-federation-concepts`, `research/260608-wikiengines-overview`,
`research/260608-c2-wiki-origins`, `research/260608-yawex-prior-art`. No new external
research was performed.

Cross-references: `spec/UseCaseCatalog.md` (UC-26–UC-59),
`workplans/SHARD-WP-0002-federation-architecture.md` (T1–T16),
`INTENT.md` (constraints), [[shard-wiki-auth-in-core-decision]].

---

## 8. Traceability

- Consolidates: nine deep dives + federation/origin research into one capability model.
- Feeds: `SHARD-WP-0002` T11 (eleven-spectra vocabulary), T12 (page-model breadth), T13
  (history confirmed), T14 (three-mode attachment taxonomy), T15 (lossy fidelity report),
  and a **new T16** (addressing, content identity, dimensional/query navigation).
- UC coverage extended in the workplan from UC-34–UC-43 to **UC-34–UC-59**.
- No UCs added (synthesis only); no boundary changes (INTENT Stability Note untouched).
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