1. Materialized view improves upon the decision support system. Justify. 2. Disc
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Question
1. Materialized view improves upon the decision support system. Justify.
2. Discuss the advantages and disadvantages of using sampling to reduce the number of data objects that need to be displayed. Would simple random sampling (without replacement) be a good approach to sampling? Why or why not?
3. Construct the inverted index. For each attribute value in each dimension, list the tuple identifiers (TIDs) of all the tuples that have that value.
4. Apply Apriori algorithm on the grocery store example with support threshold s=33.34% and confidence threshold c=60%, where H, B, K, C and P are different items purchased by customers. a) Show all final frequent itemsets. b) Specify the association rules that are generated. c) Show final association rules sorted by confidence.
TID Items 1 Bread, Milk 2 Bread, Diaper, Beer, Eggs 3 Milke, Diaper, Beer, Coke 4 Bread, Milk, Diaper, Beer 5 Bread, Milk, Diaper, CokeExplanation / Answer
Multiple Questions : Answering 1st .
Materialized views are used in data warehouses to increase the speed of queries on very large databases. Queries to large databases often involve joins between tables or aggregations such as SUM, or both. These operations are very expensive in terms of time and processing power. The type of materialized view that is created determines how the materialized view can be refreshed and used by query rewrite.
Materialized views improve query performance by precalculating expensive join and aggregation operations on the database prior to execution time and storing the results in the database. The query optimizer can use materialized views by automatically recognizing when an existing materialized view can and should be used to satisfy a request. It then transparently rewrites the request to use the materialized view. Queries are then directed to the materialized view and not to the underlying detail tables. In general, rewriting queries to use materialized views rather than detail tables results in a significant performance gain.
Thus Materialized view improves upon the decision support system with improving the performance..
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