Class Notes of CSCI 515 Data Engineering and Management (Spring 2026)
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Tuesday, May 05, 2026
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   (5-1)x(5-1) + (6-4)x(6-4) = 16 + 4 = 20


Thursday, April 30, 2026
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   IG (classification)= 0.60 - (5/10)x0.2
            = 0.5

   IG (Gini)= 0.66 - (5/10)x0.42
            = 0.5

   IG (entropy)= 1.571 - (5/10)x0.721
            = 1.571 - 0.36 = 1.211 

   Information gain( i ) = Entropy of parent table D –
       Σ( |k|/|n| × Entropy of each value k of subset table Si )


   Classification Error = 1 – max{p_j}
            = 1 - 0.8 = 0.2

 Gini Index = 1 – Σ(p_j^2)         for all j
            = 1 - 0.8x0.8 - 0.2x0.2
	    = 1 - 0.64 - 0.04 = 0.32

    Entropy = Σ[-p_j(log_2(p_j))]     for all j
            = -0.8(log(0.8)/log(2)) - 0.2(log(0.2)/log(2))      
            = 0.257 + 0.464 = 0.721

    Prob( Bus )   = 4 / 5 = 0.8        # 4B / 5 rows
    Prob( Car )   = 0 / 5 = 0.0        # 0C / 5 rows
    Prob( Train ) = 1 / 5 = 0.2        # 1T / 5 rows
   

   Classification Error = 1 – max{p_j}
            = 1 - 0.4 = 0.6

   Gini Index = 1 – Σ(p_j^2)         for all j
            = 1 - 0.4x0.4 - 2x0.3x0.3
	    = 1 - 0.16    - 0.18
	    = 0.66
	    
    Entropy = Σ[-p_j(log_2(p_j))]     for all j
            = -0.4xlog_2(0.4) - 0.3xlog_2(0.3)) - 0.3xlog_2(0.3)
	    = -0.4xlog(0.4)/log(2) - 0.3xlog(0.3)/log(2)x 2
            = -0.4x(-1.32) - 0.3x(-1.74)x2
	    = 0.528 + 1.042
            = 1.571
	    
    Prob( Bus )   = 4 / 10 = 0.4        # 4B / 10 rows
    Prob( Car )   = 3 / 10 = 0.3        # 3C / 10 rows
    Prob( Train ) = 3 / 10 = 0.3        # 3T / 10 rows


   Entropy = Σ[-p_j(log_2(p_j))]     for all j
   Gini Index = 1 – Σ(p_j^2)         for all j
   Classification Error = 1 – max{p_j}


Thursday, February 05, 2026
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Step 3:

     (4 x 1) x (1 x 4) = (4 x 4)


     0.15 x 0.25 = 0.0375


Step 2: 

      S = H+dw

           0  1 0  0       0
     =  [  0  0 1  0 ] + [ 0 ] x [ 1/4 1/4 1/4 14/ ]
          1/2 0 0 1/2      0
           0  0 0  0       1


           0  1 0  0        0   0   0   0
     =  [  0  0 1  0 ] + [  0   0   0   0 ]
          1/2 0 0 1/2       0   0   0   0
           0  0 0  0       1/4 1/4 1/4 1/4

          0   1   0   0
     = [  0   0   1   0 ]
         1/2  0   0  1/2
         1/4 1/4 1/4 1/4


Step 1:

             0  1 0  0
      H = [  0  0 1  0 ]
            1/2 0 0 1/2
             0  0 0  0


            0 1 0 0
     H' = [ 0 0 1 0 ]
            1 0 0 1
            0 0 0 0


  0.166 = 0.061 + 0.071 + 0.035

Tuesday, February 03, 2026
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shell> ls -all note.txt

-rwxr-xr-x.  1 wen.chen.hu domain users   181 Jul 12 04:48 note.txt*

 111101101 = 755 = 111 101 101
 rwxrwxrwx         --- --- ---
                    7   5   5

O: Owner permission (you)
G: Group members permission
E: Everyone else permission (including the Web)

shell> chmod 755 note.txt

shell> mysql -h undcemmysql.mysql.database.azure.com -u wenchen -p