SQL Server Web Service in a web environment architecture
Typically, you'd have a web service hosted in IIS or some other http daemon in the internal network, with a firewall hole opened up for the specified port and machine where the http web service is hosted.  

The web service, being inside, would have access to the SQL Server as required.  

This maintains protection for the SQL Server since it is not directly accessible from the dmz/website.

FYI, SOAP/xml endpoints in SQL Server were deprecated as of SQL Server 2012.