🤖 AI Summary
This work proposes an evidence-centered denotational semantic framework that reframes distributed consensus by modeling execution as higher-order evidence states induced by communication, with consensus outputs emerging as their first-order projections. Traditional output-centric descriptions of consensus protocols obscure the underlying evidential structures formed through communication; this framework unifies protocol differences as design choices concerning valid evidence, observational horizons, collapse timing, and repair mechanisms. By formalizing “collapse strategies” and integrating insights from the FLP impossibility result and topological distributed computing theory, the approach reveals a fundamental connection between consensus protocols and their evidential underpinnings, offering a novel paradigm for the analysis, comparison, and design of such protocols.
📝 Abstract
Consensus protocols are usually specified by their terminal artifact: a decided value, replicated log, or finalized prefix. This output-first view hides the communication-derived evidence that makes such artifacts safe. This paper makes that carrier explicit: distributed execution is read as an order-2 evidence state induced by communication, while classical consensus outputs are order-1 projections of that state.
Under this view, consensus protocols can be compared as collapse policies. A protocol specifies which evidence is legitimate, which finite horizon it inspects, when it projects communication evidence into a value or prefix, and how it repairs or defers collapse when the visible evidence is insufficient. The impossibility lineage supports the same distinction. FLP is not a statement that communication cannot accumulate structure; it constrains deterministic guaranteed collapse to a terminal decision under full asynchrony with one crash failure. Set agreement then exposes the width of the output carrier, and topological distributed computing asks when a history/view carrier admits a structure-preserving map to an output carrier. The contribution is not a new impossibility theorem or a replacement for protocol-specific proofs, but a denotational specification framework: consensus is collapse under evidence.