Example

• Sources: DP(A:Author,T:Title,Y:Year)

SM98(T:Title,U:URL)

• Query: Q(A,T,U,1998)

• Plan: Q(A,T,U,1998) :- DP(A,T,1998) & SM98(T,U)

HTBP: {DPbbb SM98bb}

Step 1. V={Y}

Cand: DPfff DPffb SM98ff

XX XX XX

P[1] = {DPffb SM98ff}

C[1] = DPffb

Step 2. V={A,T,Y}

Cand: SM98ff SM98bf

XX XX

P[2]={SM98bf}

C[2]=SM98bf

HTBP: {DPffb}

Step 1. V={Y}

Cand: DPfff DPffb SM98ff

XX XX

C[1] = SM98ff

Step 2. V={Y, U, T}

Cand: DPfff DPffb DPfbf DPfbb

XX XX XX

C[2] = DPfbf

HTBP: {}

Step 1. V={Y}

Cand: DPfff DPffb SM98ff

C[1] = SM98ff DPfff

Bound-is-easier

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