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Application

The user application calls ODBC functions to send SQL statements to the database and retrieve results. It performs these tasks:

  Requests a connection with a data source
  Sends SQL statements to the data source
  Defines storage areas and data types for the result sets
  Requests results
  Processes errors
  Controls transactions; requests commit or rollback operations
  Closes the connection

Driver Manager

Driver manager’s primary purpose is to load specific drivers on behalf of the user application. It may also:

  Perform a lookup in an ODBC configuration file or system registry to map the ODBC Data Source Name (DSN) to a specific DBMS driver
  Process ODBC initialization calls
  Provide entry points to ODBC functions for each specific driver
  Perform parameter and sequence validation for ODBC calls

Driver

The driver processes ODBC function calls, sends SQL statements to a specific data source, and returns results back to the application. When necessary, the driver translates and/or optimizes requests so that the request conforms to the syntax supported by the specific DBMS. The driver:

  Establishes a connection to a data source
  Sends requests to the data source
  Performs translations when requested by the user application
  Returns results to the user application
  Formats errors in standard ODBC error codes
  Manipulates cursors if necessary
  Initiates transactions, if they are explicitly required

There are two types of ODBC drivers:

  Single-tier, which processes ODBC calls and SQL statements
  Multiple-tier, which processes ODBC calls and sends SQL statements to the data source

Data Source

The data source consists of the data the user application wants to access and its associated parameters — that is, the type of operating system, DBMS, and network layer (if any) used to access the DBMS.

Summary

This chapter discussed fundamental concepts such as relational databases, SQL, and database access programming interfaces.

The next chapter discusses the Java Database Connectivity API’s role, components, and possible alternatives to it.


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