From Wikipedia:
http://en.wikipedia.org/wiki/Object-relational_mapping
Object-relational mapping (ORM, O/RM, and O/R mapping) in computer software is a programming technique for converting data between incompatible type systems in relational databases and object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language. There are both free and commercial packages available that perform object-relational mapping, although some programmers opt to create their own ORM tools.
Pros and cons
ORM often reduces the amount of code needed to be written, making the software more robust (the fewer the lines of code in a program, the fewer the errors contained within them).[1].
There are costs as well as benefits for using O/R mapping. For instance, some O/R mapping tools do not perform well during bulk deletions of data. Stored procedures may have better performance but are not portable.
