CPSC 3720 - DAY 20
MARCH 10, 2017

================================================================================

				OBJECT DESIGN
				-------------

Optimizing Access
-----------------
	
	Repeated association traversals
		Look in sequence diagrams
		Is there an often repeated traversal that goes through many
		objects
		A->B->C->D and back?
		Can an association be added to go directly from A to D?
	
	In System Design, we eliminated redundant associations to make
	subsystem decomposition clear

	It may be more efficient to add some back in
		This can be a trade off if that association is between
		different subsystems.

	"Many" Associations
		Associations with "Many" can be inefficient
			Increases search time
		Can you reduce to a one to one association?
			Can be done with a qualified association
		Order the objects on the "many" side for faster searches

Collapsing Objects
------------------

+-----------------------+			   +------------------------+
| Person		|--------------------------| SocialSecurity	    |
+-----------------------+		|	   +------------------------+
					|
					|
					|
					V

			+-----------------------------------+
			|    Person			    |
			+-----------------------------------+
			|    SSN:String			    |
			+-----------------------------------+


Delay Expensive Computations
----------------------------

	Some objects may contain large data that is expensive to compute or 
	load into memory.

	Is that data always neede?
		If not, don't always load/compute that data
		Use a proxy until that data is needed

			+-----------------------------------+
OBJECT DESIGN MODEL	|    Image			    |
BEFORE TRANSFORMATION	+-----------------------------------+
			|    filename: String data: byte[]  |
			+-----------------------------------+
			|    paint()			    |
			+-----------------------------------+
					|
					|
					V

OBJECT DESIGN MODEL	+-----------------------------------+
AFTER TRANSFORMAITON	|    Image			    |
			+-----------------------------------+
			|    filename: String data	    |
			+-----------------------------------+
			|    paint()			    |
			+-----------------------------------+
					^
					|
					|
		+---------------------------------------------------+
		|						    |
+--------------------------------+ image		 +--------------------+
| ImageProxy			 |-----------------------| RealImage	      |
+--------------------------------+ 1		 0...1   +--------------------+
| filename:String		 |			 | data:byte[]	      |
+--------------------------------+			 +--------------------+
| paint()			 |			 | paint	      |
+--------------------------------+			 +--------------------+


Caching
-------

	You may have an expensive computation that's not likely to change
	Don't recompute every time
	Store the computed value
	Include a boolean to track when those values are still valid
	***Time vs. Space Tradeoff***

Access Control Policy
---------------------

	Often considered part of System Design
	Different actors have different access
		functionality and data
	Modeled by association use cases with actors
	Which objects are shared among actors?
	Use an Access Matrix to track access control