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# Is the cost of the 4 th juicer less than the cost of its following juicers? - PowerPoint PPT Presentation

Is the cost of the 4 th juicer less than the cost of its following juicers?. Incorrect. //juicer[4]/number(cost ) < //juicer[4]/following-sibling::juicer/ number(cost ). The XPath gives the right answer for this data:. 82.00 < (234.00, 639.99) (82.00 < 234.00) or (82.00 < 639.99)

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### Is the cost of the 4th juicer less than the cost of its following juicers?

//juicer[4]/number(cost ) < //juicer[4]/following-sibling::juicer/number(cost )

The XPath gives the right answer for this data:

82.00 < (234.00, 639.99)

(82.00 < 234.00) or (82.00 < 639.99)

T or T

T

But it gives the wrong answer for this data:

82.00 < (72.00, 639.99)

(82.00 < 72.00) or (82.00 < 639.99)

F or T

T

Correct

not(//juicer[4]/number(cost ) >= //juicer[4]/following-sibling::juicer/number(cost ))

The XPath gives the right answer for this data:

not(82.00 >= (234.00, 639.99))

not((82.00 >= 234.00) or (82.00 >= 639.99))

not(F or F)

T

And it gives the right answer for this data:

not(82.00 >= (72.00, 639.99))

not((82.00 >= 72.00) or (82.00 >= 639.99))

not(T or F)

F

• If you want to do general comparison of sequences, don’t do this: A positive-operator B

• Instead, do this: not (A negative-operator B)

• Example, don’t do this: A < BInstead, do this: not(A >= B)

• Example, don’t do this: A = BInstead, do this: not(A != B)

• Example, don’t do this: A >= BInstead, do this: not(A < B)

Where A and/or B are sequences

The overwhelming temptation is to write this XPath:

10 < (20, 30)

The XPath works for this particular set of data, but change the data and it fails:

10 < (5, 30)Let’s see why: (10 < 5) or (10 < 30)

F or T

T

Instead, use this XPath:

not(10 >= (5, 30))

not((10 >= 5) or (10 >= 30))

not(F or T)

F

The overwhelming temptation is to write this XPath:

10 = (10, 10)

The XPath works for this particular set of data, but change the data and it fails:

10 = (5, 10)Let’s see why: (10 = 5) or (10 = 10)

F or T

T

Instead, use this XPath:

not(10 != (5, 10))

not((10 != 5) or (10 != 10))

not(T or F)

F