APL Protocol
Anchored Parallax Log (APL) is a protocol (v1.0) for frame-bound observation claims — statements about the world that are cryptographically inseparable from the explicit context (the frame) under which they were made.
Abstract
Cryptographic substrates such as ATL prove existence, integrity, and history of records. They do not, by themselves, prevent a record from being misread — stripped of its context, silently compared to another record produced under different assumptions, or treated as a universal fact when it is in fact situated.
APL closes this gap on the semantic layer. Every APL claim MUST reference a frame by content hash. The frame declares what was observed, how, under which assumptions, and what is explicitly not claimed. A verifier resolves the frame, checks that the claim is structurally bound to it, and reports the outcome — without deciding whether the claim is “true”.
APL is substrate-agnostic and defines the reference profile APL-on-ATL, in which metadata.apl is embedded in an ATL Receipt and APL inherits ATL’s cryptographic properties (binding, inclusion, append-only history, anchoring, offline verification).
Version 1.0 defines the minimal core: the frame-bound claim, the content-addressed frame, pairwise relation evaluation with explicit bridges, and a normative verifier contract with deterministic apl-valid / apl-invalid outcomes.
Core Principles
Frame-Bound by Construction
Every APL observation claim MUST carry a pinned frame_ref. A receipt without a resolvable frame is apl-invalid.
Content-Addressed Identity
Frames, bridges, and transformations are identified by SHA-256 of their JCS-canonicalized bytes. Aliases, URLs, and registries are for discovery only — never for identity.
No Implicit Comparison
Two claims under different frames are incomparable by default. Cross-frame comparison requires an explicit, content-addressed Bridge declaring scope, assumptions, and losses.
No Silent Semantic Loss
Transformations MUST declare preserved invariants and losses explicitly. Empty losses means “nothing is lost” — never “unknown”.
Deterministic Verifier Contract
A conforming verifier answers one core question with exactly one of apl-valid or apl-invalid. Truth is not the verifier’s job; frame binding is.
Separation of Concerns
ATL answers existence, integrity and history. APL answers frame binding, comparability discipline and declared semantic loss. Neither duplicates the other.
Architecture
