OLE DB is Microsoft's response to the object-relational database (ORDB) hybrid sometimes called a universal server. Several vendors have adopted the universal server approach. Oracle's Universal Server supplies information from its database in a variety of forms. Informix's Universal Server works with software modules to handle user needs for specific data types and ways of processing.
Many people mistakenly think Microsoft has no ORDB Management System (ORDBMS) strategy because Microsoft hasn't announced universal server capabilities for SQL Server. True, Microsoft won't create a full-fledged universal server in the near future, but Microsoft is not out of the ORDBMS race. Microsoft is simply taking a different approach, tackling the ORDBMS problem by using a middleware-based Universal Data Access (UDA) layer based on OLE DB and Microsoft Transaction Server (MTS).
The difference between a universal server and UDA is where the system stores and manages the data. Universal servers extend the relational model by adding everything plus the kitchen sink to the database. Do you need full text, image, or audio processing? Universal server advocates say, "It's in the server." Microsoft's approach keeps the underlying data in a native data store using OLE DB as the universal access mechanism, which uses MTS to manage transactions and objects. Distributed OLE DB queries are a key component for implementing a feature-rich ORDBMS environment in SQL Server.