Database Systems: Design, Implementation and Management 13th Edition solution manual
Data redundancy exists when unnecessarily duplicated data are found in the database. For example, a customer's telephone number may be found in the customer file, in the sales agent file, and in the invoice file. Data redundancy is symptomatic of a (computer) file system, given its inability to represent and manage data relationships. Data redundancy may also be the result of poorly‑designed databases that allow the same data to be kept in different locations. (Here's another opportunity to emphasize the need for good database design!)
3. What is data independence, and why is it lacking in file systems?
Data independence is a condition in which the programs that access data are not dependent on the data storage characteristics of the data. Systems that lack data independence are said to exhibit data dependence. File systems exhibit data dependence because file access is dependent on a file's data characteristics. Therefore, any time the file data characteristics are changed, the programs that access the data within those files must be modified.
Data independence exists when changes in the data characteristics don't require changes in the programs that access those data. File systems lack data independence because all data access programs are subject to change when any of the file system’s data storage characteristics – such as changing a data type -- change.
4. What is a DBMS, and what are its functions?
A DBMS is best described as a collection of programs that manage the database structure and that control shared access to the data in the database. Current DBMSes also store the relationships between the database components; they also take care of defining the required access paths to those components. The functions of a current-generation DBMS may be summarized as follows:
- The DBMS stores the definitions of data and their relationships (metadata) in a data dictionary; any changes made are automatically recorded in the data dictionary.
- The DBMS creates the complex structures required for data storage.
- The DBMS transforms entered data to conform to the data structures in item 2.
- The DBMS creates a security system and enforces security within that system.
- The DBMS creates complex structures that allow multiple‑user access to the data.
- The DBMS performs backup and data recovery procedures to ensure data safety.
- The DBMS promotes and enforces integrity rules to eliminate data integrity problems.
- The DBMS provides access to the data via utility programs and from programming languages interfaces.
- The DBMS provides end-user access to data within a computer network environment.
5. What is structual independence, and why is it important?
Structural independence exists when data access programs are not subject to change when the file's structural characteristics, such as the number or order of the columns in a table, change. Structural independence is important because it substantially decreases programming effort and program maintenance costs.
6. Explain the differences between data, information, and a database
Data are raw facts. Information is processed data to reveal the meaning behind the facts. Let’s summarize some key points:
- Data constitute the building bocks of information.
- Information is produced by processing data.
- Information is used to reveal the meaning of data.
- Good, relevant, and timely information is the key to good decision making.
- Good decision making is the key to organizational survival in a global environment.
7. What is the role of a DBMS, and what are its advantages? What are its disadvantages?
A database management system (DBMS) is a collection of programs that manages the database structure and controls access to the data stored in the database. Figure 1.2 (shown in the text) illustrates that the DBMS serves as the intermediary between the user and the database. The DBMS receives all application requests and translates them into the complex operations required to fulfill those requests. The DBMS hides much of the database’s internal complexity from the application programs and users. The application program might be written by a programmer using a programming language such as COBOL, Visual Basic, or C++, or it might be created through a DBMS utility program.