The ever-increasing movement towards implementing complex SOA-based applications has triggered a direct attention of leading industry researchers and practitioners to the subject of layering in such applications, in general, and the relationship between the fields of database engineering and SOA, in particular. Common notion of interoperability, loose-coupling between consumers and providers, and complexity-hiding, and demands for enabling extensive reuse of application services to address unforeseen business requirements for new user types, for new types of information and for new composite views has brought to the forefront the concept of Data Services Layer (DSL) as a distinct architectural layer. DSL is an essential part of an application architecture that combines data access functions and corresponding database structures and promises ensuring the next harvest for SOA ROI.