Windows Open Service Architecture is one of the mainstays of Microsoft Windows: the methods of abstraction of core services.
For each extension, Windows Open Services Architecture defines an API and an SPI, as well as a universal interface (usually placed in a single DLL) that both comply to.
These then transparently let the operating system speak to device drivers, database managers, and other low level entities.
These extensions include, among others, ODBC (called the "crowning jewel of WOSA"), TAPI, WOSA/XFS, SAPI and MAPI, and their supporting services, as well as the abstraction of access to printers, modems, and networking services, which run identically over TCP/IP, IPX/SPX, and NetBEUI.
This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.