What Are Web Services?

Web services are software systems designed to support interoperable machine-to-machine interaction over a network using standardized messaging protocols and interface descriptions. They enable applications running on different platforms, written in different programming languages, and operated by independent organizations to exchange data and invoke operations through a well-defined, network-accessible interface. The defining characteristic of a web service is that its interface is described in a machine-readable format and its messages are transmitted over standard internet protocols, making integration possible without prior bilateral negotiation of proprietary formats.

Web services emerged in the late 1990s and early 2000s as enterprises sought a way to expose internal application functionality to external partners and to compose distributed systems from loosely coupled components. The architectural patterns that followed split into two dominant styles: the XML-based SOAP model, supported by a formal stack of W3C and OASIS standards, and the resource-oriented REST model built directly on HTTP. Both remain in active use, and the choice between them reflects the tradeoffs between formal contract enforcement and operational simplicity.

SOAP and Service Description

SOAP (Simple Object Access Protocol) is an XML-based messaging protocol that defines the structure of request and response envelopes, independent of the transport layer, though HTTP is the most common carrier. SOAP services expose their operations through a Web Services Description Language (WSDL) document, a formal XML schema that specifies available methods, their input and output types, and the binding to a network endpoint. WSDL-based contracts allow client libraries and SDKs to be generated automatically from a service definition, reducing integration effort and enforcing type safety across system boundaries. The combination of SOAP and WSDL became the basis for enterprise service buses and the broader web services stack standardized through WS-* specifications covering security, transactions, and reliable messaging.

REST Architecture

Representational State Transfer (REST) is an architectural style for distributed systems derived from principles observed in the design of the Web itself. A RESTful web service exposes resources identified by URIs and supports operations through HTTP methods: GET to retrieve a representation, POST to create, PUT or PATCH to update, and DELETE to remove. Responses typically carry JSON or XML representations, and the stateless nature of each request simplifies horizontal scaling. Research comparing SOAP and REST web services for enterprise application integration shows that REST services generally incur lower latency and implementation overhead, while SOAP services offer stronger formal contracts. An analysis of public REST web service APIs documents common design patterns, versioning strategies, and error-handling conventions across large API ecosystems.

Service-Oriented Architecture

Web services are the technical substrate of service-oriented architecture (SOA), a design approach that structures an enterprise system as a collection of loosely coupled, independently deployable services that communicate through a shared message bus or API gateway. SOA principles encourage service reuse across business processes, decoupling the consuming application from the implementing service. Cloud computing has extended this model into microservices architectures, where individual services are deployed in containers, scaled independently, and accessed asynchronously through message queues or event streams as well as synchronous HTTP calls. An industry view on SOA and web services published through IEEE Xplore traces the adoption patterns and practical implementation challenges enterprises encountered in transitioning to service-based architectures.

Applications

Web services have applications across many technology domains, including:

• Cloud computing platforms exposing infrastructure resources through REST and SOAP APIs
• IoT device integration, including webcams and sensors reporting data to cloud back-ends
• Financial systems exchanging payment and settlement messages between institutions
• Healthcare interoperability, with HL7 FHIR defining RESTful APIs for clinical data exchange
• Enterprise application integration connecting ERP, CRM, and supply chain systems