# DeFi composability: reusing capabilities and inheriting dependencies Composability lets one application use another application’s tokens, contracts or data as a building block. It can combine useful operations, but it also carries dependencies forward. A vault share used as collateral still depends on the vault, its assets, price interpretation and the lending market that accepts it. Evidence: [ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20); [ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626); [Oracles](https://ethereum.org/developers/docs/oracles/) Canonical: https://degreesofsatoshi.com/encyclopedia/defi-composability/ Published: 2026-10-02 Substantively modified: 2026-10-02 Independently verified by an automated reviewer: 2026-10-02T18:17:57.897Z AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied. ## Key facts - **Common interface:** ERC-20 enables token reuse across applications. ([ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20)) - **Claim layer:** ERC-4626 shares represent a claim on underlying vault assets. ([ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626)) - **Changing dependency:** A dependency may itself have an upgradeable implementation. ([Proxy contracts](https://docs.openzeppelin.com/contracts/5.x/api/proxy)) ## A standard interface makes integration possible An application can call a token’s transfer interface without inventing a new transfer format for each asset. A vault interface similarly exposes shares and underlying-asset operations. Shared interfaces reduce the mechanical work needed to connect contracts. They do not prove identical economic behavior. A token can have issuer restrictions, and a vault can have strategy losses or withdrawal limits. Compatibility with a method signature is a smaller claim than compatibility with every assumption an integrator makes. Evidence: [ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20); [ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626) ## Map each dependency in a composed position Consider a vault share deposited as lending collateral. The position depends on the vault’s assets and strategy, its share conversion and withdrawal rules, the oracle’s interpretation of that share, the lending market’s thresholds, and any relevant upgrade authority. An accurate token interface lets these contracts connect; it does not independently verify the assumptions each one makes about the others. A withdrawal limit or changed share value in the vault can affect the collateral position downstream. Record this chain of dependencies when assessing the combined product. Evidence: [ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626); [Pool](https://aave.com/docs/aave-v3/smart-contracts/pool); [Using Data Feeds](https://docs.chain.link/data-feeds/overview); [Proxy contracts](https://docs.openzeppelin.com/contracts/5.x/api/proxy) ## Atomic execution does not remove continuing dependencies A single successful transaction can connect several operations, but the resulting position persists afterward. Its dependency can be upgraded, its withdrawal rules can apply, and its underlying assets can change in value. Atomic execution only answers whether that transaction completed as a unit. A useful research record lists each layer, what it promises, who controls changes and how to exit. Count independent underlying exposures rather than dashboard rows: several receipts can ultimately depend on the same asset, oracle or administrative authority. Evidence: [Proxy contracts](https://docs.openzeppelin.com/contracts/5.x/api/proxy); [ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626) ## Questions ### Do standard interfaces make the combined system safe? No. Standards specify interaction conventions. They do not validate every economic assumption, dependency, implementation or future upgrade in a composition. Evidence: [ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20); [ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626); [Proxy contracts](https://docs.openzeppelin.com/contracts/5.x/api/proxy) ## Claims and scope ### defi-composability-quick-answer Composability lets one application use another application’s tokens, contracts or data as a building block. It can combine useful operations, but it also carries dependencies forward. A vault share used as collateral still depends on the vault, its assets, price interpretation and the lending market that accepts it. Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null} ### defi-composability-fact-common-interface Common interface: ERC-20 enables token reuse across applications. Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null} ### defi-composability-fact-claim-layer Claim layer: ERC-4626 shares represent a claim on underlying vault assets. Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null} ### defi-composability-fact-changing-dependency Changing dependency: A dependency may itself have an upgradeable implementation. Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null} ## Sources - [ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20) — Ethereum Improvement Proposals. The token spending allowance is separate from a website connection. Locator: Methods: approve, allowance, transferFrom. Retrieved: 2026-10-02. - [ERC-4626: Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626) — Ethereum Improvement Proposals. Vault shares, assets, previews, withdrawal limits and rounding. Locator: Specification; Security Considerations. Retrieved: 2026-10-02. - [Oracles](https://ethereum.org/developers/docs/oracles/) — ethereum.org contributors. External observations and the trust boundary between data and consensus. Locator: What is an oracle?; The oracle problem. Retrieved: 2026-10-02. - [Proxy contracts](https://docs.openzeppelin.com/contracts/5.x/api/proxy) — OpenZeppelin. Proxy implementation changes and the authorization requirement. Locator: TransparentUpgradeableProxy; UUPSUpgradeable. Retrieved: 2026-10-02. - [Pool](https://aave.com/docs/aave-v3/smart-contracts/pool) — Aave. Collateralization, available liquidity and liquidation operations. Locator: supply; withdraw; borrow; liquidationCall. Retrieved: 2026-10-02T17:03:44.834Z. - [Using Data Feeds](https://docs.chain.link/data-feeds/overview) — Chainlink. Feed update conditions, chain/feed-specific configuration and consumer checks. Locator: Heartbeat and deviation thresholds; Data quality. Retrieved: 2026-10-02T17:38:46.139Z. ## Revision history - 2026-10-02: First publication after primary-source research and independent automated verification. - 2026-10-02: Expanded explanation: Map each dependency in a composed position. Worked examples are illustrative; source checks and independent verification are recorded separately. ## Cite this entry Degrees of Satoshi editorial project. “DeFi composability: reusing capabilities and inheriting dependencies.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/defi-composability/