What is a web service?
A web service is a service offered by a remote device to another device. The communication happens via Web, hence the name Web. In a Web service, HTTP protocol is used for device-to-device communication. It is used as transport protocol for transferring content as XML, JSON, Protocol Buffers etc.
Web services are implemented using as SOAP / REST based. Please find below picture for better understanding:
What is a Micro service?
Microservice is that the complex service is de-composed into small, light-weight, independent services. These services are small and independent, decoupled and fitted for doing a small task. These services should be individually deployable, scalable, monitored etc. Micro services are granular, small, decoupled web services.
Well web service and microservice are not totally unrelated terms. It is possible that web service is a microservice and vice versa. The difference lies on how we develop, deploy, provision, manage, monitor etc. A lot depends on how we want to develop, deploy, provision, manage, scale etc. the services.
Micro service Architecture
Micro service Architecture usually varies from a monolithic application or service bundle. A monolithic application/service means a big centralized package deployed on a single server instance. For example , package all the services in a single .ear file and deployed on a single server.
Micro service architecture is small deployable instances on multiple distributed environment. For example, service functionality broken down into individually small .ear files and deployed on multiple server instances , cloud environment etc.