What is Middleware in system architecture?

• A. A firewall appliance.
• B. A programming language.
• C. A database management system.
• D. An interface between systems, often between an application and multiple underlying legacy systems.

Answer: (D)

Middleware is an interface layer that sits between applications and other systems, enabling communication and integration across different environments. It often acts as a bridge between an application and multiple underlying legacy systems, handling data translation, protocol differences, and the orchestration of various services so the app can interact with diverse back-end components without managing each connection directly. Examples include message brokers, enterprise service buses, API gateways, and adapters that connect to older systems. The other options describe different technologies: a firewall appliance is a security device that filters traffic; a programming language is a tool for building software; a database management system manages data storage and retrieval.