THE PERL DATABASE INTERFACE (DBI).


The DBI Architecture.

   
Perl Script / Program

   
DBI



   
DBD::Informix
DBD::Oracle
DBD::MySQL



   
Oracle
RDBMS
Oracle
RDBMS
MySQL
RDBMS

The Perl DBI Architecture can then be seen as being split into a number of distinct layers.

The Program Layer
The Program Layer consists of the Perl
code that makes calls to the DBI API
Methods.
   
Perl Script / Program
using DBI API methods



The API Layer
The DBI passes method calls from the
Perl script to whatever driver has
been specified in the connection string.
   
DBI API
DBI Core



The Driver Layer
The Driver Layer contains protocol drivers
that implement various DBI methods
using private interface functions.
   
Other
Drivers
Oracle
Driver
XYZ
Driver





The Database Layer
The Database Layer consists of the
actual database engines such as
Oracle, MySQL, etc.
   
Oracle
Engine
XYZ
Engine

ODBC

The Perl DBI Architecture is essentially similar to ODBC (the Open Database Connectivity). The ODBC equivalent of the Perl DBI is the ODBC Driver Manager, and the ODBC Drivers are the equivalent of Perl DBD drivers. A number of Perl DBI modules exist for ODBC use, e.g. DBD::ODBC (written in C) and Win32::ODBC (written in C++).

ADO

The ADO (ActiveX Data Objects) is yet another Microsoft Layer built on top of a layer. Essentially, ADO is a data access API, and in a Microsoft environment, works fine as another layer on top of ODBC. Access to Microsoft databases such as SQL Server is not onerous using ADO, however as with a number of other Microsoft technologies, they are dependent on all layers working, and unfortunately, unlike Perl and DBI, the level of robustness in the Microsoft technologies is less impressive. The other drawback is during the debugging process. The more layers in the system, frequently the harder and longer it takes to resolve issues with the code.

It is however, possible to use ADO from Perl by using the Win32::OLE module and even better, the DBD::ADO module.


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