Web 服务： Web 服务是可以通过 Internet 访问并通过 XML 编码规范其对应关系的任何位服务。客户通过发送请求(大部分为 XML 消息)来调用 Web 服务，然后服务发回 XML 响应。 Web 服务通过网络进行通信，HTTP 是两个框架之间最广泛认可的网络方法。 Web 服务相当于 SOA(面向服务的体系结构)并且从根本上依赖于度量，例如 XML-RPC 和 SOAP(简单对象访问协议)。
组件：所有标准 Web 服务都使用以下组件工作。
- SOAP(简单对象访问协议)
- UDDI(通用描述、发现和集成)
- WSDL(Web 服务描述语言)
Web API： API代表应用程序编程接口。它是各种程序用来在它们之间进行通信的通信约定和子程序的集合。开发人员可以利用不同的 API 设备来使其程序更简单和更简单。同样，API 鼓励开发人员以熟练的方法构建他们的产品程序。因此，简单来说，API 决定了编程段应该如何相互关联。它是一组协议和时间表，其反应以数据中的 JSON 或 XML 形式返回。 API 可以使用任何类型的通信约定，并且不像 Web 服务那样受到限制。
Web 服务和 API 之间的区别：
| Web Services | Web API |
|---|---|
| Web services are a type of API, which must be accessed through a network connection. | APIs are application interfaces, implying that one application can communicate with another application in a standardized manner. |
| Web service is used for REST, SOAP and XML-RPC for communication. | API is used for any style of communication. |
| All Web services are APIs. | APIs are not web services. |
| It doesn’t have lightweight design, needs a SOAP convention to send or receive data over the system. | It has a light-weight architecture furthermore, useful for gadgets which have constrained transmission capacity like smart phones. |
| It provides supports only for the HTTP protocol. | It provides support for the HTTP/s protocol: URL Request/Response Headers, and so on. |
| It is not open source, however, can be devoured by any customer that comprehends xml. | It is an open source and also ships with .NET framework. |
| Web service supports only XML. | API supports XML and JSON. |
| Web Services can be hosted on IIS. | Web API can be hosted only on IIS and self. |