ODBC Architecture
Open Database Connectivity Without Compromise !

The ODBC architecture has four components:

  • Application - (Spreadsheet, Word processor, Data Access & Retrievable Tool, Development Language etc.) Performs processing by passing SQL Statements to and receiving results from the ODBC Driver Manager.
  • Driver Manager - a Dynamic Link Library that Loads drivers on behalf of an application.
  • Driver - a Dynamic Link Library that Processes ODBC function calls received from the Driver Manager, submitting the resultant SQL requests to a specific data source, and returns results to the application. If necessary, the driver modifies an application's request so that the request conforms to syntax supported by the associated DBMS.
  • Data Source Consists of a DBMS, the operating system the DBMS runs on, and the network (if any) used to access the DBMS.
  • The Driver Manager and Driver appear to an application as one unit that processes ODBC function calls.

Types of Drivers

ODBC defines two types of drivers:

  • Single-tier The driver processes both ODBC calls and SQL statements.
  • Multiple-tier The driver processes ODBC calls and passes SQL statements to the data source.

One system can contain both types of configurations. The following paragraphs describe single-tier and multiple-tier configurations in more detail.

Single-Tier Configuration

In a single-tier implementation, the database is processed directly by the driver. The driver processes SQL statements and retrieves information from the database. One example of a single-tier implementation is a driver that manipulates desktop database systems such as -DBASE, Paradox, Fox Pro etc.
The following diagram shows two types of single-tier configurations - one stand alone and one that uses a network. In a single tier driver network environment data access software resides on the PC, this implies that query resolution intelligence resides on the client.

Multiple-Tier Configuration

In a multiple-tier configuration, the driver sends SQL requests to a server that processes SQL requests.

The application, driver, and Driver Manager reside on one system, typically called the client. The database and the software that controls access to the database typically reside on another system, typically called the server. This implies that query resolution intelligence resides on the server.

A variant of the multiple-tier configuration is a gateway architecture, where the driver passes SQL requests to a gateway process. The gateway process sends the requests to the data source. The gateway in this scenario can be a piece of hardware or data access software in the form of a low level interface to foreign databases provided by the RDBMS vendor.

The following diagram shows two types of multiple-tier configurations. From the perspective of an application, both configurations are identical.

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