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Driver Architecture

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Driver architecture falls into two categories, depending on which software processes SQL statements:

  • File-Based Drivers The driver accesses the physical data directly. In this case, the driver acts as both driver and data source; that is, it processes ODBC calls and SQL statements. For example, dBASE drivers are file-based drivers because dBASE does not provide a stand-alone database engine the driver can use. It is important to note that developers of file-based drivers must write their own database engines.

  • DBMS-Based Drivers The driver accesses the physical data through a separate database engine. In this case the driver processes only ODBC calls; it passes SQL statements to the database engine for processing. For example, Oracle drivers are DBMS-based drivers because Oracle has a stand-alone database engine the driver uses. Where the database engine resides is immaterial. It can reside on the same machine as the driver or a different machine on the network; it might even be accessed through a gateway.

Driver architecture is generally interesting only to driver writers; that is, driver architecture generally makes no difference to the application. However, the architecture can affect whether an application can use DBMS-specific SQL. For example, Microsoft Access provides a stand-alone database engine. If a Microsoft Access driver is DBMS-based - it accesses the data through this engine - the application can pass Microsoft Access-SQL statements to the engine for processing.

However, if the driver is file-based - that is, it contains a proprietary engine that accesses the Microsoft Access .mdb file directly - any attempts to pass Microsoft Access-specific SQL statements to the engine are likely to result in syntax errors. The reason is that the proprietary engine is likely to implement only ODBC SQL.

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