# Ordering Key or Sequence

> The requirement that each event carry a key or sequence number that fixes its position in order.

Record: `lexicon:ordering-key-or-sequence`
Kind: constraint
Layer: [Causality Core](https://banes-lab.com/records/layer/causality-core.md)
Canonical: https://banes-lab.com/ontology/lexicon#lexicon-ordering-key-or-sequence

Listed in [Lexicon terms](https://banes-lab.com/api/records/lexicon.md), after [Correct Stateful Processing](https://banes-lab.com/records/lexicon/correct-stateful-processing.md) and before [Unordered Parallel Consumption](https://banes-lab.com/records/lexicon/unordered-parallel-consumption.md).

## Category

- [Causality / Ordering / Distributed Time](https://banes-lab.com/records/lexicon-category/causality-ordering-distributed-time.md)

## Required by

- [Event Ordering](https://banes-lab.com/records/architecture/event-ordering.md)

## Linked from

- [Causality / Ordering / Distributed Time](https://banes-lab.com/ontology/principles/architecture-category-causality-ordering-distributed-time.md)