(第3空)System analysis is traditionally done top-down using structured analysis based on( ).Object-oriented analysis focuses on creation of models.The three types of the analysis model are( ).There are two substages of object-oriented analysis.( )focuses on real-world things whose semantics the application captures.The object constructed in the requirement analysis shows the( )of the real-world system and organizes it into workable pieces.( )addresses the computer aspects of the application that are visible to users.The objects are those which can be expected to vary from time to time quite rapidly.