Notes for 4-10

Database

PL/SQL

Anonymous and named PL/SQL block

• Anonymous PL/SQL block
  • Need to compile every time
  • Not stored
• Named PL/SQL block
  • Can be stored in DB

Stored Procedure

Grammar:

Procedure ::= CREATE [OR REPLACE] PROCEDURE ProcedureName '(' Parameters ')' (AS|IS) RETURN ReturnType DECLARE Declaration BEGIN Body END ';'
Parameters ::= Nothing | Parameter {, Parameter}
Parameter ::= ParameterName (IN|OUT|IN OUT) Type ':=' DefaultValue

• Note:
  • In the parameter list, varchar cannot be specified with a length.
  • MySQL has no AS|IS in the procedure, and IN/OUT is put before the parameter name.
  • In MySQL ,one has to change the delimiter before defining a procedure or function.

Loop statement

• for x in [Reverse] 1…20 loop … end loop;
• while … loop … end loop; To escape from a loop:
• exit when …;

Conditional statement

• if … then … elseif … end if;

Cursor

• Used to process a set of records. PL/SQL record variable can only store one record at a time.
• Technically, it acts like an iterator, which means one cannot process multiple records at the same time(though we can store them as a whole).
• In declaration, a cursor is declared with a SELECT statement, and we can use this cursor to access the data returned by that SELECT statement
• A cursor is bind to one specific SELECT clause, that is, one cannot bind it to another SELECT statement
• The SELECT statement is and only is executed when the cursor is OPENed(see below).
• CLOSE the cursor to free the memory space. Synopsis:

1. Declaration

cursor cursor_name is select statement;

2. Open cursor

OPEN cursor_name;

3. Get the data

FETCH cursor_name into variable;

• The cursor will move forward, just like python’s next function do.

4. Check if there is no more entry

IF NOT cursor_name%FOUND THEN …;

5. Close the cursor

CLOSE cursor_name;

6. For loop Unique to Oracle. No need to open, close, or fetch from a cursor.

FOR variable in cursor_name LOOP – do something to the variable END LOOP;

Artificial Intelligence

Knowledge base && Inferrence

* Truth table

* Brute force search

* Forward chaining
    * reliable
    * completeness
        * -> only have these two properties for the knowledge bases able to be expressed with Horn clauses
        * Horn clause: a disjunction of literals with at most one unnegated literal
            * E.g. {% katex %}
\neg x_1 \vee \neg x_2 \vee \cdots \vee x_n \vee u
{% endkatex %}

* Backward chaining
    * To prove q, with p->q now prove p
    * Avoid repeating by check if a clause is already proved or disproved

Misc

Panning derives from panorama.

4/11 Record

Programming Languages

Polymorphic Functions

• Static: cost grows exponentially with parameters
• Dynamic:
  • supply a tag when calling the function

Example: Overloading Equality

1. Equality was overloaded as an operator
2. Make type of equality fully polymorphic
3. Make equality polymorphic in a limited way
   • (==) :: ''t -> ''t -> Bool, ''t is a type t with equality
   • will be a static error if t is not Eq type

Type Classes

1. Merchanism in Haskell
2. Dictionary-passing style implementation [ESOP1988]
   • Type class declaration – dictionary
   • Name of a type class method – label in the dictionary
   • Parametric overloading – passing the dictionary to the function

class Show a where
    show :: a -> String

instance Show Bool where
    show True = "True"
    show False = "False"

print :: Show a => a -> IO ()
print x = putStrLn $ show x

type 'a show = {show: 'a -> string}
let show_bool : bool show = 
{
    show = function
        | true -> "True"
        | false -> "False"
}

let print : 'a show -> 'a -> unit =
    fun {show=show} x -> print_endline (show x)

Smalltalk: subtyping

• Object -> super class -> method table

• If interface A contains all of interface B, then A objects can also be used as B objects

  • need to look up all instances(members) at runtime

Javascript has the same problem

• v8 engine: hidden class

function Person(first_name, last_name) {
    this.first_name = first_name;
    this.last_name = last_name;
}

var potus = new Person('D.', 'Trump');
var potrf = new Person('V.', 'Putin');

Computer Architecture

Optimizing cache

Merging write cache

DRAM and SRAM

Misc

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