We are starting to implement workday and had a question regarding whether workday can call an external webservice.
It appears there is an API. https://community.workday.com/api
Hereis the web services documentation. https://community.workday.com/custom/developer/API/index.html
Workday offers an open, standards-based SOAP API for programmatic access to our On-Demand Business Management Services. The following directory provide the API Documentation for our multi-tenant SOAP-based web services with corresponding WSDL and XML Schemas (XSD's).