SOAP (Simple Object Access Protocol) is a standardised, XML-based messaging protocol for exchanging structured information between applications, typically over HTTP but also over other transports. It defines an envelope structure with a header and body, supports remote procedure calls and document-style messaging, and is described by WSDL contracts and extended by the WS-* specifications for security, transactions, and reliable messaging. SOAP underpinned the first generation of enterprise web services and remains common in regulated and legacy integration scenarios, contrasting with the lighter, resource-oriented REST style.
Overview
- SOAP standardises how messages are framed, routed, and processed independent of platform or language.
- It supports both remote-procedure-call and document-style exchange, described formally by WSDL contracts.
- The WS-* family extends it with security, reliable messaging, and transactions for enterprise needs.
- It powered the first wave of interoperable web services and persists in regulated and legacy integrations.
Key aspects
- Envelope, header, and body structure provide a consistent message contract.
- WSDL describes operations, types, and bindings for tooling and code generation.
- Transport independence allows operation over HTTP, message queues, and SMTP.
- Extensibility through WS-* addresses security and reliability formally.
Applications
- Enterprise application and B2B system integration.
- Financial, government, and healthcare services with strict contract and security needs.
- Legacy Service-Oriented Architecture estates and middleware buses.
- Interoperability between heterogeneous platforms via standardised contracts.