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Given a stream of updates about items drawn from a universe {1,...,n}, the stream's fre- quency vector f e R" is the vector whose i'th component fi equals the frequency of item i in the stream. For example, for the stream ((add, 5), (add, 7), (add, 5), (add, 7), (delete, 7)) with universe {1,….,7}, its frequency vector is (0,0,0,0,2, 0, 1). A streaming algorithm is said to maintain a linear sketch of size k if it stores in memory' Af for a matrix A € R**n that is fixed at the initialization. (a) Show that the algorithm discussed in class for frequency estimation is a linear sketch. What is the matrix A in this case? (b) Suppose a streaming algorithm is a linear sketch. Assume the matrix A mentioned above is explicitly known to the algorithm. Explain how the algorithm should update its storage each time a stream update comes of the form (add, i) or (delete, i).

Given a stream of updates about items drawn from a universe {1,...,n}, the stream's fre- quency vector f e R" is the vector whose i'th component fi equals the frequency of item i in the stream. For example, for the stream ((add, 5), (add, 7), (add, 5), (add, 7), (delete, 7)) with universe {1,….,7}, its frequency vector is (0,0,0,0,2, 0, 1). A streaming algorithm is said to maintain a linear sketch of size k if it stores in memory' Af for a matrix A € R**n that is fixed at the initialization. (a) Show that the algorithm discussed in class for frequency estimation is a linear sketch. What is the matrix A in this case? (b) Suppose a streaming algorithm is a linear sketch. Assume the matrix A mentioned above is explicitly known to the algorithm. Explain how the algorithm should update its storage each time a stream update comes of the form (add, i) or (delete, i).

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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Given a stream of updates about items drawn from a universe {1,...,n}, the stream's fre- quency vector f e R" is the vector whose i'th component fi equals the frequency of item i in the stream. For example, for the stream ((add, 5), (add, 7), (add, 5), (add, 7), (delete, 7)) with universe {1,...,7}, its frequency vector is (0,0,0,0, 2, 0, 1). A streaming algorithm is said to maintain a linear sketch of size k if it stores in memory' Aƒ for a matrix A e R**n that is fixed at the initialization. (a) Show that the algorithm discussed in class for frequency estimation is a linear sketch. What is the matrix A in this case? (b) Suppose a streaming algorithm is a linear sketch. Assume the matrix A mentioned above is explicitly known to the algorithm. Explain how the algorithm should update its storage each time a stream update comes of the form (add, i) or (delete, i).
Transcribed Image Text:Given a stream of updates about items drawn from a universe {1,...,n}, the stream's fre- quency vector f e R" is the vector whose i'th component fi equals the frequency of item i in the stream. For example, for the stream ((add, 5), (add, 7), (add, 5), (add, 7), (delete, 7)) with universe {1,...,7}, its frequency vector is (0,0,0,0, 2, 0, 1). A streaming algorithm is said to maintain a linear sketch of size k if it stores in memory' Aƒ for a matrix A e R**n that is fixed at the initialization. (a) Show that the algorithm discussed in class for frequency estimation is a linear sketch. What is the matrix A in this case? (b) Suppose a streaming algorithm is a linear sketch. Assume the matrix A mentioned above is explicitly known to the algorithm. Explain how the algorithm should update its storage each time a stream update comes of the form (add, i) or (delete, i).
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