15.2 The Vector Space Model

• ad-hoc retrieval system $B$GHs>o$K$h$/MQ$$$i$l$kdocument, query $B$rB?document $B$H(B query $B$N$J$93QEY(B(cosine)$B$GN`;wEY$r7W;;(B (Figure 15.3)
• term $\rightarrow$ word $B$b(B phrases $B$b(B term $B$H$$$&C10L$G07$&(B

	$BF`NI(B	$B5~ET(B	$BBg:e(B	$B?@8M(B	$BEl5~(B	$\cdots$	$BJ!2,(B
Doc 1		1		1
Doc 2			1		3		1
Doc 3		2					1
Doc 4	1			2	1
Doc 5	2			1			1
$\vdots$
Doc N		1		3			1

$B8!:wMW5a%Y%/%H%k(B $\vec{q}$ = {(1 $\cdot$ $BF`NI(B), (2 $\cdot$ $B5~ET(B), (1 $\cdot$ $B?@8M(B)}

SIM(q,Doc 1)	=	1 $\cdot$ 0 + 2 $\cdot$ 1 + 1 $\cdot$ 1	=	3
SIM(q,Doc 2)	=	1 $\cdot$ 0 + 2 $\cdot$ 0 + 1 $\cdot$ 0	=	0
SIM(q,Doc 3)	=	1 $\cdot$ 0 + 2 $\cdot$ 2 + 1 $\cdot$ 0	=	4
SIM(q,Doc 4)	=	1 $\cdot$ 1 + 2 $\cdot$ 0 + 1 $\cdot$ 2	=	3
SIM(q,Doc 5)	=	1 $\cdot$ 2 + 2 $\cdot$ 0 + 1 $\cdot$ 1	=	3
$\vdots$
SIM(q,Doc N)	=	1 $\cdot$ 0 + 2 $\cdot$ 1 + 1 $\cdot$ 3	=	5