True /False/MCQ Questions

Distributed Database System is the combination of database system and Computer Network Technology.

Integration with centralization could achieve database distribution.

A global schema is a single, connected view of homogeneous databases.

In global-as-view (GAV) systems, the GCS definition exists, and each GCS is treated as a view definition over it.

Schema matching algorithms deal with both structural homogeneity and semantic homogeneity among the matched schemas.

Key conflict occur when the same object is represented by an attribute in one schema and by an entity (relation) in another.

Learning-based approaches formulate the problem as one of classication where concepts from various schemas are classied into classes according to their similarity.

The directory of a distributed DBMS is itself a distributed database.

A view is a static window in the sense that it doesnt reects all updates to the database.

In relational systems, authorizations can be uniformly controlled by database developers using high-level constructs.

In general, semantic integrity constraints are rules that represent the knowledge about the properties of an application.

The role of a distributed query processor is to map a high-level query on a centralized database into a sequence of database operators on relation fragments.

Cost function typically refers to computing resources such as disk I/Os, CPUs, and communication networks.

In a distributed system, relational algebra is enough to express execution strategies.

The communication cost is the time needed for exchanging data between sites participating in the execution of the query.

Complexity is O(n²) for unary operators, where n denotes the relation cardinality, if the resulting tuples may be obtained independently of each other.

The centralized Decision approach is simpler but requires knowledge of the entire distributed database.

The semijoin operator has the important property of reducing the size of the operand relation.

One way to simplify a query is to eliminate redundant predicates.

Query optimization consists of finding the best ordering of operators in the query, including communication operators that minimize a cost function.