OOAD

OOAD stands for Object Orient Analysis and Design.

A good book on this topic is,

Head First Object oriented analysis & Design:

http://books.google.co.in/books?id=-QpmamSKl_EC&dq=object+oriented+analysis+and+design+%2B+head+first&printsec=frontcover&source=bn&hl=en&ei=WHEHTLG6KsOxrAey_9CKAQ&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBwQ6AEwAw#v=onepage&q&f=false

1. Great Software meets customer expectation.2
2. Great Software is well-designed and well-coded. It's easy to maintain, reuse and extend.

In strucuture programming we design modules which are loosely coupled. In Object oriented programming, objects should be designed so that they are loosely coupled. This allows object to behave independately. This improves reusability, since object can be reused anywhere. This also improves flexibility, since the object can be changed independentaly of each other.