What is top down approach and bottom up for VLSI design?

Top down approach is based on Chip level flow, If the design is small then we can opt for this approach . Bottom down approach is hierarchical based chip design flow, If our Design is big, then , the chip is divided in to small manageable modules, it is similar to "Divide and Conquer approach", Finish the small manageable modules , so that the run time will be controlled, and then finally integrate in to one-chip.