CSC151.01 2006S, Class 39: Association Lists and Searching

Admin:
* Due: HW12.
* Assigned: HW13.
  * Remember: There's a homework due every Tuesday and every Friday
* Reading: Searching.
* Don't forget Thurday's Thursday Extra on the GIMP.  Noon.  
  Free Pizza.
* Don't forget to vote!
* Extended office hours due to preregistration.  
  Signup outside office.

Overview:
* Databases and dictionaries.
* Lists as dictionaries.
* assoc, a procedure for searching lists.
* Variants of Association Lists.
* Lab.

Databases are one of the primary applications of computers
* A way of storing information
* And categorizing that information
* That supports searching/lookup based on categories

Simplest database: Dictionary (or Encyclopedia :-)
* Collection of Name/Value pairsa
* Primary operation: "Look up name"
* Often, the name is called a "key"

How can we represent a dictionary in Scheme?
* A list (or vector) of pairs
* A list of lists
* Assumption: The car of each element is the key

Lab!

/Reflection/

* It's amazing how many errors remain in labs.
* What preconditions should assoc have?
* What happens if the capitalization doesn't match (e.g., the 
  desired key and the key in the list are the same, but capitalized
  differently)?
* And what can we do about it?
How do we support "look up by key"?