The term single source relates to the concept of storing all content used by many users for many deliverable in one place. The advantage of single sourcing is that changes to single sourced content propagate to all deliverables that reference it when the deliverable is rebuilt.
Content can be single sourced using a Content Management System (CMS) or an operating system’s standard file management system. A CMS provides a rich set of features for access and revision control. The propriety nature of CMS system brings some disadvantages. The cost of these systems; training, customization, and format conformance restriction to name few; are balance against the open flexibility and limited features associated with a file management system when deciding which system to use.
DITA-Word uses a file management system to leverage its inherent open flexibility.