What is a key difference between Web Services and REST APIs?

The distinction between Web Services and REST APIs is significant in understanding how data is exchanged over the web. Web Services, particularly SOAP (Simple Object Access Protocol) based services, typically utilize XML as the messaging format. This focus on XML is due to the strict standards and protocols that SOAP adheres to, which include XML for messages and typically require a WS-* (Web Services) stack for security and transactions.

In contrast, REST (Representational State Transfer) APIs are more flexible and can utilize various formats such as JSON, XML, HTML, or plain text. However, the defining characteristic of Web Services in this context is their reliance on XML, which is what makes the statement regarding their exclusive support for XML correct.

The other options do not accurately represent the characteristics of Web Services or REST APIs. For instance, stating that Web Services use only JSON is incorrect because it strictly adheres to XML. Similarly, REST APIs are not SOAP-based; they are a different architectural style altogether, which makes the assertion that they are SOAP-based inaccurate. Lastly, while SQL might be used for database operations, it is not inherently a feature of REST APIs, which typically rely on standard HTTP methods for operations. Thus, the emphasis on XML support by Web Services is crucial