# Subject/Subscriber Contract

> The requirement of an agreed interface by which subjects notify and subscribers receive updates.

Record: `lexicon:subject-subscriber-contract`
Kind: constraint
Layer: [Design Patterns Core](https://banes-lab.com/records/layer/design-patterns-core.md)
Canonical: https://banes-lab.com/ontology/lexicon#lexicon-subject-subscriber-contract

Listed in [Lexicon terms](https://banes-lab.com/api/records/lexicon.md), after [Stable Element Hierarchy](https://banes-lab.com/records/lexicon/stable-element-hierarchy.md) and before [Uniform Handler Interface](https://banes-lab.com/records/lexicon/uniform-handler-interface.md).

## Category

- [Behavioral Patterns](https://banes-lab.com/records/lexicon-category/behavioral-patterns.md)

## Required by

- [Observer Pattern](https://banes-lab.com/records/architecture/observer-pattern.md)

## Linked from

- [Behavioral Patterns](https://banes-lab.com/ontology/principles/architecture-category-behavioral-patterns.md)