What is the difference between XSD and WSDL?

Solution 1:

WSDL (Web Services Description Language) describes your service and its operations - what is the service called, which methods does it offer, what kind of in parameters and return values do these methods have?

It's a description of the behavior of the service - it's functionality.

XSD (Xml Schema Definition) describes the static structure of the complex data types being exchanged by those service methods. It describes the types, their fields, any restriction on those fields (like max length or a regex pattern) and so forth.

It's a description of datatypes and thus static properties of the service - it's about data.

Solution 2:

XSD defines a schema which is a definition of how an XML document can be structured. You can use it to check that a given XML document is valid and follows the rules you've laid out in the schema.

WSDL is a XML document that describes a web service. It shows which operations are available and how data should be structured to send to those operations.

WSDL documents have an associated XSD that show what is valid to put in a WSDL document.