SQL Server Protocols is the layer of network technologies that enables client applications to talk to the server:
These SQL protocols and components are necessary to allow for communications with SQL Server by the clients.
Database Connectivity for .NET
ADO.NET is the core data access technology for .NET languages. Use the System.Data.SqlClient namespace to access SQL Server, or providers from other suppliers to access their stores. Use System.Data.Odbc or System.Data.Oledb to access data from .NET languages using other data access technologies. Use System.Data.Dataset when you need an offline data cache in client applications. It also provides local persistence and XML capabilities that can be useful in web services.
Native Database Connectivity: ODBC
ODBC is the primary native data access API, for applications written in C and C++, for SQL Server. There is an ODBC driver for most data sources. Other languages (including COBOL, Perl, PHP and Python) employ ODBC and it is widely used in data integration scenarios. The ODBC Driver comes with tools such as sqlcmd and bcp. The sqlcmd utility lets you run Transact-SQL statements, system procedures, and SQL scripts. The bcp utility bulk copies data between an instance of Microsoft SQL Server and a data file in a user-specified format. The bcp utility can be used to import large numbers of new rows into SQL Server tables or to export data out of tables into data files.
Native Database Connectivity: OLE DB
OLE DB uses COM to provide data access capabilities.
OLE DB provider for SQL Server has been deprecated.
Database Connectivity for Java
In its continued commitment to interoperability, Microsoft provides a Java Database Connectivity (JDBC) driver for use with SQL Server. The Microsoft JDBC Driver for SQL Server is available to all SQL Server users at no additional charge, and provides access to various versions of SQL Server and SQL Azure from any Java application, application server, or Java-enabled applet. This driver is a Type 4 JDBC driver that provides database connectivity through the standard JDBC application program interfaces (APIs).
Database Connectivity for PHP
The SQL Server Driver for PHP is designed to enable reliable, scalable integration with SQL Server for PHP applications. The SQL Server Driver for PHP is a PHP 5 extension that allows the reading and writing of SQL Server data from within PHP scripts. It provides interfaces for accessing data in all Editions of SQL Server 2005 and later (including Express Editions) as well as SQL Azure, and makes use of PHP features, including PHP streams to read and write large objects.
"Connecting Application Developers to SQL Server"