# ASL/INDEXES/1 -- Index Taxonomy and Relationships

Status: Draft
Owner: Architecture
Version: 0.1.0
SoT: No
Last Updated: 2025-01-17
Tags: [indexes, content, structural, materialization]

**Document ID:** `ASL/INDEXES/1`
**Layer:** L2 -- Index taxonomy (no encoding)

**Depends on (normative):**

* `ASL/1-CORE-INDEX`
* `ASL-STORE-INDEX`

**Informative references:**

* `ASL/SYSTEM/1`
* `TGK/1`

---

## 0. Conventions

The key words **MUST**, **MUST NOT**, **REQUIRED**, **SHOULD**, and **MAY** are to be interpreted as in RFC 2119.

ASL/INDEXES/1 defines index roles and relationships. It does not define encodings or storage layouts.

---

## 1. Purpose

This document defines the minimal set of indexes used by ASL systems and their dependency relationships.

---

## 2. Index Taxonomy (Normative)

ASL systems use three distinct indexes:

### 2.1 Content Index

Purpose: map semantic identity to bytes.

```
ArtifactKey -> ArtifactLocation
```

Properties:

* Snapshot-relative and append-only
* Deterministic replay
* Optional tombstone shadowing

This is the ASL/1-CORE-INDEX and is the only index that governs visibility.

### 2.2 Structural Index

Purpose: map structural identity to a derivation DAG node.

```
SID -> DAG node
```

Properties:

* Deterministic and rebuildable
* Does not imply materialization
* May be in-memory or persisted

### 2.3 Materialization Cache

Purpose: record previously materialized content for a structural identity.

```
SID -> ArtifactKey
```

Properties:

* Redundant and safe to drop
* Recomputable from DAG + content index
* Pure performance optimization

---

## 3. Dependency Rules (Normative)

Dependencies MUST follow this direction:

```
Structural Index -> Materialization Cache -> Content Index
```

Rules:

* The Content Index MUST NOT depend on the Structural Index.
* The Structural Index MUST NOT depend on stored bytes.
* The Materialization Cache MAY depend on both.

---

## 4. PUT/GET Interaction (Informative)

* PUT registers structure (if used), resolves to an ArtifactKey, and updates the Content Index.
* GET consults only the Content Index and reads bytes from the store.
* The Structural Index and Materialization Cache are optional optimizations for PUT.

---

## 5. Non-Goals

ASL/INDEXES/1 does not define:

* Encodings for any index
* Storage layout or sharding
* Query operators or traversal semantics