Microsoft Data Access Components

The Microsoft SQL Server Network Library (also known as Net-Lib) is used by the Microsoft SQL Server to read and write data using many different network protocols. Though Net-Lib is specific to the SQL Server, Microsoft includes it with MDAC. The SQL Server uses the Open Data Services (ODS) library to communicate with Net-Lib, which interfaces directly with the Windows NT operating system line's Win32 subsystem. The SQL Server Network Library is controlled through the use of a Client Network Utility, which is bundled with the SQL Server.

Each Net-Lib supported network protocol has a separate driver (not to be confused with a device driver), and has support for a session layer in its protocol stack. There are two general types of Net-Lib: the primary and the secondary. The primary Net-Lib consists of a Super Socket Net-Lib and the Shared Memory Net-Lib, while there are numerous secondary Net-Libs, including TCP/IP and named pipes network libraries (named pipes are a method of communicating with other processes via a system-persistent pipeline that is given an identity). The Microsoft OLE DB Provider for SQL Server (SQLOLEDB) communicates via primary Net-Libs.

The Super Socket Net-Lib deals with inter-computer communications and coordinates the secondary Net-Libs – though the TCP/IP secondary Net-Lib is an exception in that it calls on the Windows Sockets 2 API directly. The Banyan VINES, AppleTalk, ServerNet, IPX/SPX, Giganet, and RPC Net-Libs were dropped from MDAC 2.5 onwards. The Network Library router had the job of managing all these protocols, however now only the named pipes secondary Net-Lib is managed by the router. The Super Socket Net-Lib also handles data encryption via the use of the Windows SSL API.

The Shared Memory Net-Lib, on the other hand, manages connections between multiple instances of SQL Server that exist on one computer. It uses a shared memory area to communicate between the processes. This is inherently secure; there is no need for data encryption between instances of SQL Server that exist on one computer as the operating system does not allow any other process access to the instances' area of shared memory.

Net-Lib is also able to support the impersonation of a logged in user's security context for protocols that support authenticated connections (called trusted connections). This allows Net-Lib to provide an integrated logon authentication mechanism via the use of Windows Authentication. Windows Authentication is not supported on Windows 98 or Windows Me.

OLE DB (also called OLEDB or OLE-DB) allows MDAC applications access to different types of data stores in a uniform manner. Microsoft has used this technology to separate the application from the data store that it needs to access. This was done because different applications need access to different types and sources of data, and do not necessarily need to know how to access technology-specific functionality. The technology is conceptually divided into consumers and providers. The consumers are the applications that need access to the data, and the provider is the software component that exposes an OLE DB interface through the use of the Component Object Model (or COM).

OLE DB is the database access interface technology used by MDAC. OLE DB providers can be created to access such simple data stores as a text file or spreadsheet, through to such complex databases as Oracle and SQL Server. However, because different data store technology can have different capabilities, OLE DB providers may not implement every possible interface available. The capabilities that are available are implemented through the use of COM objects