A homogenous database is one that uses the same DBMS at each node. A heterogeneous database is one that may have a different DBMS at each node.
42. What is a distributed database?
A distributed database is a single logical database that is spread across more than one node or locations that are all connected via some communication link.
43. Explain the difference between two and three-tier architectures?
Three-tier architecture includes a client and two server layers.
The application code is stored on the application server and the database is stored on the database server. A two-tier architecture includes a client and one server layer. The database is stored on the database server.
44. Briefly describe the three types of SQL commands?
Data definition language commands are used to create, alter, and drop tables. Data manipulation commands are used to insert, modify, update, and query data in the database. Data control language commands help the DBA to control the database.
45. List some of the properties of a relation?
Relations in a database have a unique name and no multivalued attributes exist. Each row is unique and each attribute within a relation has a unique name. The sequence of both columns and rows is irrelevant.
46. Explain the differences between an intranet and an extranet?
An Internet database is accessible by everyone who has access to a Web site. An intranet database limits access to only people within a given organization.
47. What is SQL Deadlock?
Deadlock is a unique situation in a multi user system that causes two or more users to wait indefinitely for a locked resource.
48. What is a Catalog?
A catalog is a table that contains the information such as structure of each file, the type and storage format of each data item and various constraints on the data .The information stored in the catalog is called Metadata.
49. What is data ware housing & OLAP?
Data warehousing and OLAP (online analytical processing) systems are the techniques used in many companies to extract and analyze useful information from very large databases for decision making .
50. Describe the three levels of data abstraction?
Physical level: The lowest level of abstraction describes how data are stored.
Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
View level: The highest level of abstraction describes only part of entire database.