33. Both deferred update and immediate update requires redoing all write item op

Question

33. Both deferred update and immediate update requires redoing all write item operations of transactions a. started after the checkpoint. b. uncommitted (active) at system crash. c. committed after the last checkpoint. d. committed before the last checkpoint. 34. Data warehousing differs from transaction-based databases in that it is oftene a. distributed. b. serving thousands of users. c. good enough for businesses. d. read-access only. 35. Statistical database security techniques prohibits a. the use of statistical queries. b. the use of aggregate functions.- c. getting statistics from individual information. d. inferring individual information from statistical queries. 36. The assumption that a MAC number is registered by a manufacturer and cannot be used another manufacturer is represented by the functional dependency a. MAC-> manufacturer. b. manufacturer ->MAC. c. both. d. neither. 37. An attribute is nonprime if it is not a member of any a. partial key. b. primary key.^ d. candidate key.* 38. In BCNF, every nontrivial FD has a superkey on the left-hand side. 3NF allows additional FDs if their right-hand side is ae c. nonprime attribute.e d. prime attribute. a. b. key.4 39. The frequent-pattern tree growth algorithm is more efficient than the apriori algorithm in analyzing a. social-network data. b. market-basket data. c. three-dimensional data. d. graph data. 40. In the basic timestamp ordering, r1x fails ife a. readTS(X) > TS(1). b. read TS(X) IS(1). c. write. ?$(X) IS(1). el

Explanation / Answer

33. Both deferred update and immediate update requires redoing all write_item operations of transactions uncommitted at system crash.

Immediate update

In the immediate update techniques, the database may be updated by the operations of a transaction immediately, before the transaction reaches its commit point. However, these operations are typically recorded in the log on disk by force-writing before they are applied to the database, so that recovery is possible.

When immediate update is allowed, provisions must be made for undoing the effect of update operations on the database, because a transaction can fail after it has applied some updates to the database itself. Hence recovery schemes based on immediate update must include the capability to roll back a transaction by undoing the effect of its write operations.

Deferred update

The idea behind deferred update is to defer or postpone any actual updates to the database itself until the transaction completes its execution successfully and reaches its commit point. During transaction execution, the updates are recorded only in the log and in the transaction workspace. After the transaction reaches its commit point and the log is force-written to disk, the updates are recorded in the database itself. If a transaction fails before reaching its commit point, there is no need to undo any operations, because the transaction has not affected the database in any way.

34.

Data ware housing differs from transaction based databases in that it is often read access only

A transaction database query allows to read and modify operations, while a data warehouse query needs only read only access of stored data. Users of a data warehouse need only read access to data but, need the access to be fast over a large volume of data.

A data warehouse is constructed by integrating data from multiple heterogeneous sources that support analytical reporting, structured and/or ad hoc queries, and decision making. Data warehousing involves data cleaning, data integration, and data consolidations.

35.

Statistical database security techniques prohibits getting statistics from individual information.

Statistical databases are used to produce statistics about various populations.

The database may contain confidential data about individuals, which should be protected from user access. However, users are permitted to retrieve statistical information about the populations, such as averages, sums, counts, maximums, minimums, and standard deviations.

Statistical database security techniques must prohibit the retrieval of individual data. This can be achieved by prohibiting queries that retrieve attribute values and by allowing only queries that involve statistical aggregate functions such as COUNT, SUM, MIN, MAX, AVERAGE, and STANDARD DEVIATION. Such queries are sometimes called statistical queries.

36.

The assumption that a MAC number is registered by a manufacturer and cannot be used by another manufacturer is represented by the functional dependency MAC->manufacturer

MAC->manufacturer means that a MAC number is used only by a particular manufacturer

manufacturer->MAC does not hold since a manufacturer may produce different products with different MAC.

A set of attributes X functionally determines a set of attributes Y if the value of X determines a unique value for Y.

X -> Y holds if whenever two tuples have the same value for X, they must have the same value for Y

For any two tuples t1 and t2 in any relation instance r(R): If t1[X]=t2[X], then t1[Y]=t2[Y]

37.

An attribute is non prime if it is not a member of any candidate key.

In the relational model of databases, a candidate key of a relation is a minimal superkey for that relation; that is, a set of attributes such that:

1. the relation does not have two distinct tuples (i.e. rows or records in common database language) with the same values for these attributes (which means that the set of attributes is a superkey)

2. there is no proper subset of these attributes for which (1) holds (which means that the set is minimal).

The constituent attributes are called prime attributes. Conversely, an attribute that does not occur in ANY candidate key is called a non-prime attribute.

38.

In BCNF every non trivial functional dependency has a super key on the left hand side. 3NF allows additional FDs if their right hand side is a prime attribute.

In BCNF, for every non-trivial FD, either the left hand is a superkey or the right hand side is part of a key (any key).

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.