Programming the Perl DBI

Storage Managers and Layers

Modern databases, no matter which methodology they implement, are generally composed of multiple layers of software. Each layer implements a higher level of functionality using the interfaces and services defined by the lower-level layers.

For example, flat-file databases are composed of pools of data with very few layers of abstraction. Databases of this type allow you to manipulate the data stored within the database by directly altering the way in which the data is stored within the data files themselves. This feature gives you a lot of power and flexibility at the expense of being difficult to use, minimal in terms of functionality, and nerve-destroying since you have no safety nets. All manipulation of the data files uses the standard Perl file operations, which in turn use the underlying operating system APIs.

DBM file libraries, like Berkeley DB, are an example of a storage manager layer that sits on top of the raw data files and allows you to manipulate the data stored within the database through a clearly defined API. This storage manager translates your API calls into manipulations of the data files on your behalf, preventing you from directly altering the structure of the data in such a manner that it becomes corrupt or unreadable. Manipulating a database via this storage manager is far easier and safer than doing it yourself.

You could potentially implement a more powerful database system on top of DBM files. This new layer would use the ...