A data processing chain is the sequence of parties and steps that personal data passes through, from collection to storage, sharing, analysis, and deletion. Each link in the chain may be a controller, a processor, or another service provider, and each one can change how data is protected and who is responsible for it.
In cyber security, the chain matters because attackers often target the weakest link: an exposed vendor, a misconfigured cloud service, or a subcontractor with broader access than needed. Defenders use the same idea to reduce risk by mapping data flows, limiting access, encrypting transfers, and setting clear contracts and logs for every handoff. A well understood chain also helps during incidents, because teams can quickly identify where data went, who handled it, and which controls failed.