$7\mathrm{.}19$ What is a DFD$?$ Why do systems analysts use DFDs$?$

$7\mathrm{.}20$ Explain the rules for drawing good DFDs$.$

$7\mathrm{.}21$ What is decomposition? What is balancing? How can you determine if DFDs are not balanced?

$7\mathrm{.}22$ Explain the convention for naming different levels of DFDs$.$