What is API?
An API (Application Programming Interface) is a defined set of methods and protocols that enables software applications to communicate and exchange data via standardised endpoints.
Application Programming Interface
Technical Definition: An API is a defined set of methods and protocols serving as an interface between software applications, enabling structured data exchange via specific endpoints (URLs). In building automation, REST APIs using the HTTP protocol and exchanging data in JSON format are dominant.
Why it matters: Without open APIs, systems become closed islands. A well-documented API turns every system into a composable building block – a prerequisite for a modern, open integration architecture.
HubMind’s view: We require open, documented APIs for every system we integrate. A vendor that refuses to provide one is creating vendor lock-in by design.
Read more: Why standardisation is critical for integration.
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Example and trade-offs
An operations tool can fetch temperatures, send a setpoint change or request an alarm through an API. For the integration to last, more than an endpoint is needed: formats, errors, permissions, rate limits and lifecycle must be clear to both sides. An API may be openly documented while still requiring an agreement, authentication or paid access.
HubMind’s view
Our point: an API is an information contract, not an integration promise. Why: without version rules and ownership, every change becomes a surprise for the next system in the chain. Recommendation: require an OpenAPI description, test environment, authentication, compatibility policy and export of relevant history before approving a system.
Related concepts: REST API, JSON, OPC UA and data governance.
External references: OpenAPI Specification and IETF HTTP Semantics.
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