DataFlex SQL Server Driver

The DataFlex SQL Server Driver is used to access SQL Server databases from DataFlex programs. SQL Server is a Relational Database Management System (RDBMS) from Microsoft. It runs on Windows platforms offering Client/Server functionality to database applications.

Many existing DataFlex applications, without change, will be able to use SQL Server for data storage. Others require changes in order to perform well with SQL Server.

SQL Server

Microsoft SQL Server is a high-performance, Client/Server Relational Database Management System (RDBMS). It was designed to support high-volume transaction processing (i.e., online order entry, inventory, accounting, or manufacturing), as well as data warehousing and decision-support applications (i.e., sales analysis applications). SQL Server runs on Microsoft Windows Server-based networks and can be installed as a desktop database system on a Window Workstation.

A relational database can be viewed as a set of tables that can be manipulated in accordance with the relational model of data. It contains a set of objects used to store, manage, and access data. SQL is a standardized language for defining and manipulating data in a relational database.

In a database Client/Server environment, the following two processes communicate: the database client and the database server. The Client/Server architecture allows all data requests of a client to be executed by one or several servers. Thus, data manipulation is separated, carried out by the Client, and the server carries out data management/recording. This offers greater integrity and speed in the processing of information.

The DataFlex SQL Server Driver uses the Call Level Interface (CLI) to connect DataFlex programs to SQL Server. CLI is an Application Programming Interface (API) in which functions are provided for applications to process dynamic SQL statements. CLI enables DataFlex to connect to SQL Server databases, issue SQL statements and return data and status information without being compiled against a specific database.

DataFlex and SQL Server

The Data Access Database API expects database drivers to support a certain set of attributes for a table. These attributes may or may not be available in the supported back-end. If such an attribute is not available in the back-end it needs to be stored somewhere outside of the back-end database. The API uses “intermediate files” to store such information. The contents of an intermediate file are partly API defined and partly driver specific.

The DataFlex SQL Server Driver will use the SQL Server back-end for its attributes whenever possible. Some information can only be stored in the intermediate file because SQL Server does not support the attribute essential to DataFlex. The DataFlex SQL Server Driverexpects an intermediate file to be present for every table that is accessed through it.

A design goal of the DataFlex SQL Server Driver was that a DataFlex program should be able to switch the underlying database to SQL Server without the need to adjust that program.

Automatic Client Selection

A client server database environment uses two processes to handle database connections. A database server process runs the database and stores the actual data. A client process communicates with the server process to retrieve or modify data.

Microsoft creates new clients from time to time. It is possible for a machine to have multiple SQL Server clients installed.  A client can connect to database servers from a different version (even if that server has a newer version).

The login logic of the DataFlex SQL Server driver automatically chooses the highest client version installed on the workstation (even to connect to older versions of the database server). The following clients are recognized and supported:

See Also

DataFlex SQL Drivers