WCF (ADO.Net) Data Services is a development framework for the creation and consumption of OData services. You would use this to develop custom Web service integration
points for existing database applications or your own custom database applications.
SQL Server Master Data Services (MDS) is an application platform that brings together high-level building blocks for implementing Master Data Management applications.
MDS is itself a database application. It creates and manages a central master data repository database for you and provides a user interface and a number of other MDM application features such that you do not need to build them yourself. MDS
exposes a WCF-based Web services API, so you could use WCF Data Services to integrate MDS with other database applications.