Introduction to DBI

Databases

• Relational
• SQL
• Examples:
  • Oracle
  • Informix
  • Sybase
  • Ingres
  • Postgres
  • mSQL
  • MySQL
• It's hard to write portable DB apps:
  • The SQL spec is incomplete, so each vendor implements proprietary extensions
  • No standard for front ends
  • No standard for APIs
    • The Bad Old Days: oraperl, sybperl, ingperl
    • Vendor-specific APIs for other languages, too
  • An application could work with only one RDBMS
  • It was built on (and could use only) that vendor's API

DBI: A Vendor-Neutral Solution

• DBI
• Written and maintained by Tim Bunce
• Provides a single, common API that encapsulates each vendor's specific API calls
• Example: The DBI call connect calls:
  • Oracle's ora_login
  • MySQL's mysql_connect
  • Whatever's appropriate for any other database
• DBI is an object class
• Its sub-classes are a set of DBDs (DataBase Drivers), e.g.
  • DBD::Oracle
  • DBD::Informix
  • DBD::mysql
• Usage:

  #! /opt/perl5/bin/perl
  use DBI; # Load the DBI
  use DBD::mysql; # This program uses MySQL

• The payoff:
  • If you write code that uses no RDBMS-specific calls...
  • If you use only generic SQL...
  • Then replacing one DBD with another is easy.
  • You won't have to rewrite your program when your pointy-haired boss makes you switch databases.

Review

What are the prerequisites for writing portable database applications?