What is the role of a WSDL file in Salesforce integrations?

A WSDL (Web Services Description Language) file plays a crucial role in Salesforce integrations by describing the web service capabilities. It serves as a contract between the service provider and the consumer, detailing how to communicate with the web service. This includes information about the operations (functions) available, the parameters required for each operation, the data types used, and the protocols supported, such as SOAP.

When Salesforce is integrated with other systems, the WSDL file provides a clear understanding of how to interact with those services effectively. Developers can generate client-side code from the WSDL, allowing them to make calls to the web service without needing to manually handle the underlying details of the communication process.

The other roles mentioned in the options do not pertain to the function of a WSDL file. While defining the database structure might refer to a database schema, and infrastructure security would concern protocols like SSL, these aspects are not adequately captured within a WSDL file. Furthermore, user interface details are not relevant in the context of WSDL; instead, they focus more on how data is structured and exchanged in web service communications. Thus, WSDL's primary focus is clearly on describing web service capabilities.