BDUF is: Big Design Up Front
Taken from: http://en.wikipedia.org/wiki/Big_Design_Up_Front
Big Design Up Front (BDUF) is a software development approach in which the program’s design is to be completed and perfected before that program’s implementation is started. It is often associated with the waterfall model of software development.
Arguments for Big Design Up Front
Proponents of waterfall model argue that time spent in designing is a worthwhile investment, with the hope that less time and effort will be spent fixing a bug in the early stages of a software product’s lifecycle than when that same bug is found and must be fixed later. That is, it is much easier to fix a requirements bug in the requirements phase than to fix that same bug in the implementation phase, as to fix a requirements bug in the implementation phase requires scrapping at least some of the implementation and design work which has already been completed.
Arguments against Big Design Up Front
Critics (notably those who practice agile software development) argue that BDUF is poorly adaptable to changing requirements and that BDUF assumes that designers are able to foresee problem areas without extensive prototyping and at least some investment into implementation.
They also assert that there is an overhead to be balanced between the time spent planning and the time that fixing a defect would actually cost. This is sometimes termed analysis paralysis.
If the cost of planning is greater than the cost of fixing then time spent planning is wasted.
Continuous Deployment, Automatic Updates, Fault Tolerance, Lisp’s Read-eval-print loop and related ideas seek to substantially reduce the cost of defects in production so that they become cheaper to fix at run-time than to plan out at the beginning.
Also, in most projects there is a significant lack of comprehensive written (or even well known) requirements. So in BDUF a lot of assumptions are made that later prove to be false but are designed and possibly already coded.