System Interfaces

System interfaces are the defined connection points through which two or more IT systems, applications, or infrastructure components exchange data, trigger processes, or share state. An interface specifies the contract between systems: what data is sent, in what format, over what protocol, and under what conditions. Interfaces are not the systems themselves — they are the boundaries and bridges between them. Modern interfaces take many forms: REST APIs (request-response over HTTP/S), event-driven message queues (asynchronous publish-subscribe), database links, file-based transfers (EDI, SFTP batch), and streaming data pipelines. Every interface has three core elements: a protocol (how data travels), a schema or contract (what the data looks like), and an error-handling strategy (what happens when something goes wrong). A system interface IS: a governed connection point with defined inputs, outputs, protocols, and error behaviors. A system interface IS NOT: the internal logic of either connected system, the network layer those systems run on, or an informal ad-hoc connection — though ungoverned connections exist in most environments and must be identified and managed.