OAuth is commonly used for secure, token-based authentication in web services, providing a standardized way for third-party applications to obtain limited access to a web service.

An X.509 certificate is often used in web services to establish a secure connection between the client and server, providing authentication and encryption.

Microservices impact traditional SOA practices by shifting towards decentralized and smaller services. While both share common principles, microservices emphasize smaller, independent services that operate autonomously, challenging some aspects of the centralized and monolithic nature associated with traditional SOA practices.

SOAP (Simple Object Access Protocol) is an XML-based protocol used for exchanging structured information in web services.

Token-based authentication is preferred in RESTful APIs as it does not require maintaining session state on the server.

Input validation is a security principle that involves validating and sanitizing user inputs to prevent security vulnerabilities.

The element in a WSDL file is used to define the data types that will be used by the web service, specifying the structure of the input and output messages.

REST is typically more efficient in caching due to its stateless nature. Stateless communication allows for easier caching implementation as each request from a client to a server is independent, reducing complexity and enhancing caching efficiency in distributed systems.

REST APIs commonly return data in JSON format, whereas GraphQL provides more flexibility in the format of returned data.

When integrating with legacy systems, XML might be preferred due to its rich schema definition and strong data typing. XML allows for precise data representation, which is crucial for interoperability and compatibility with existing systems that may rely on specific data structures.