---
title: Parallel Composition
slug: parallel-composition
url: https://templeton.host/lexicon/parallel-composition/
type: defined-term
inDefinedTermSet: https://templeton.host/lexicon
author: Andrew Templeton
---

# Parallel Composition

## Definition

A pipeline topology where a source fans out to N independent branches that later merge. Two variants. Parallel-AND requires every branch to clear (joint yield is still the product, no improvement over serial - only latency drops). Parallel-OR accepts when any branch clears (yield approaches 1 fast, the redundant-verifier pattern).

## Why this term exists

Parallel-AND is what most people mean by "parallelize the pipeline" - and it does not improve correctness, only throughput. Parallel-OR is the underused redundancy pattern: when false-rejects are cheap, running two verifiers in parallel and accepting on either catches misses.

## See also

- [DAG Topology widget](https://templeton.host/widgets/dag-topology)
- [Serial Composition](https://templeton.host/lexicon/serial-composition)
- [Verifier-Producer](https://templeton.host/lexicon/verifier-producer)

Canonical URL: https://templeton.host/lexicon/parallel-composition/