a. The primary key cannot be null. b. None of these choices is correct. c. Most tables need a foreign key. d. Tables are linked by using foreign keys.

What is a scenario where records stored in a computer frequently need to be checked

Consider the usual algorithm to convert an infix expression to a postfix expression. suppose that you have read 10 input characters during a conversion and that the stack now contains these symbols: (5 points) | | | + | | ( | bottom |_*_| now, suppose that you read and process the 11th symbol of the input. draw the stack for the case where the 11th symbol is

The idea that, for each pair of devices v and w, there’s a strict dichotomy between being “in range” or “out of range” is a simplified abstraction. more accurately, there’s a power decay function f (·) that specifies, for a pair of devices at distance δ, the signal strength f(δ) that they’ll be able to achieve on their wireless connection. (we’ll assume that f (δ) decreases with increasing δ.) we might want to build this into our notion of back-up sets as follows: among the k devices in the back-up set of v, there should be at least one that can be reached with very high signal strength, at least one other that can be reached with moderately high signal strength, and so forth. more concretely, we have values p1 ≥ p2 ≥ . . ≥ pk, so that if the back-up set for v consists of devices at distances d1≤d2≤≤dk, thenweshouldhavef(dj)≥pj foreachj. give an algorithm that determines whether it is possible to choose a back-up set for each device subject to this more detailed condition, still requiring that no device should appear in the back-up set of more than b other devices. again, the algorithm should output the back-up sets themselves, provided they can be found.\