I. Design Model: Determining Visibility (Larman Ch. 18)
 A. visability between objects (18.1)
  When is visibility necessary?
  So if a Register sends messages to a ProductCatalog, which must
     be visible to which?
 B. Visibility (18.2)
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        KINDS OF VISIBILITY

Object B is visible to A if:

 - attribute visibility

 - parameter visibility

 - local visibility

 - global visibility
   
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     Which would you use if you wanted a relatively permanent
     connection?
     which would you use if you didn't want a permanent connection?
     how would you create a local visibility?
     how would you achieve a global visibility?