# Single-Instance Need

> A precondition that exactly one instance of a type must exist across the system.

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

Listed in [Lexicon terms](https://banes-lab.com/api/records/lexicon.md), after [Related Product Variants](https://banes-lab.com/records/lexicon/related-product-variants.md) and before [Subclass-Controlled Creation](https://banes-lab.com/records/lexicon/subclass-controlled-creation.md).

## Category

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

## Required by

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

## Linked from

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