21. Which of the following is true of a distributed DBMS? (a) There is always one central server that distributes processing to other servers. (b) Table columns may be stored on servers in different physical locations. (c) Data can always be redistributed for optimal query processing. (d) All of the above. 22. What is the purpose of classification algorithms? (a) Determine the most likely value of an unknown categorical field of a record. (b) Determine the most likely value of an unknown numerical field of a record. (c) Use data in which all field values are known to produce classification rules to be applied to new data. (d) a and c (e) b and c (f) a, b, and c 23. Which property is guaranteed by the two-phase locking protocol? (a) serial schedules (b) serializable schedules (c) recoverable schedules (d) avoiding cascading rollback 24. What information can an inverted index contain? (a) the presence of words in documents (b) the number of times words appear in documents (c) the relative positions at which words appear in documents (d) the number of documents a word appears in (e) some of the above (f) all of the above 25. What kind of conflict (if any) is present in the transaction schedule below? r1(A);w1(A);r2(A);w2(A);r2(B);w2(B);commit2;r1(B);w1(B);commit1 (a) read-write conflict (b) write-read conflict (c) write-write conflict (d) no conflict 26. With regards to pages in the buffer pool, which pair of buffer management policies give the most efficient operation of the recovery manager? (a) stealing and forcing (b) stealing and no forcing (c) no forcing and stealing (d) no forcing and no stealing