第8章データ管理

There are many advantages to using a DBMS such as controlling redundancy in data storage. When the same piece of data is held in two separate places in the database, data redundancy can occur. DBMS improves development and maintenance efforts, sharing of data among multiple users, and restricting unauthorized access to data. For example, only the DBA staff uses privileged commands and facilities providing persistent storage for program objects (e.g., object-oriented DBMSs make program objects persistent), providing storage structures (e.g., indexes) for efficient query processing. Additionally, a DBMS provides data independence, which helps the user to easily make changes to the database.

There are two types of data independence. The first, physical data independence, separates the conceptual level from the physical level (e.g., using a new storage device such as a hard drive); the second, logical data independence, separates any changes in the data from the data format. DBMS provides integrity rules by adding a primary key to guarantee that every record is unique. DBMS allows you to manage structured, semistructured, and unstructured data.

Data that have been organized into a formatted database and have relational keys (e.g., relational data) are called structured data. Data that are not organized in a formatted database but have some organized properties (e.g., XML data) are called semistructured data. Data that are not organized in a formatted database and do not have organized properties (e.g., PDF) are called unstructured data. The DBMS provides a backup copy of the entire database, which is backed up as decided, perhaps once a day. The backup copy should be stored in a secured location and is used to restore the database in the event of failure, loss, or damage to the original data.

Databases, database technology, and “big data” (complex datasets) have a tremendous impact in industries such as banking, insurance, retail, health care, real estate, e-commerce, law, education, and more recently, social networks. Data collection is also impacting advancements in the fields of medicine, environmental studies, science, and mobile technology.

Can you think of any other industries in which the use of big data is surprising? Does big data benefit the users or the collectors? Will big data enable more scientific research and/or discoveries? Why or why not?

DBMS includes various components as in Figure 8.6. DBMS interface is the main line of communication between the database and the user. There are many types of interfaces such as web-based, stand-alone query language, command line, forms-based, graphical user interface (GUI), natural language, admin, and network.

A connection manager manages reports, books, objects, and batches. For each database, the connection manager provides the connection name, data source type, and value. A security manager is a collection of processes used to secure the database from threats. The data description language (DDL) compiler translates statements in a high-level language into low-level instructions that the query evaluation engine understands. A query processor acts as an intermediary between users and the DBMS data engine to communicate query requests including DML compiler, query parser, query rewriter, query optimizer, and query executor. A storage manager is a program that is responsible for editing, storing, updating, deleting, and retrieving data in the database such as transaction manager, buffer manager, lock manager, and recovery manager. DBMS utilities are a set of utilities for managing and controlling database activities such as loading utility, reorganization utility, performance-monitoring utilities, user management utilities, and backup and recovery utility. Figure 8.7 illustrates the navigation window, results window, log window, and query window.