1、计算机与信息学院 本科毕业设计（论文） - 1 - 外文资料翻译 原文部分 Database Management (From http:/ Database (sometimes spelled database) is also called an electronic database, referring to any collections of data, or information, that is specially organized for rapid search and retrieval by a computer. Databases are structured
2、 to facilitate the storage, retrieval modification and deletion of data in conjunction with various data-processing operations. Database can be stored on magnetic disk or tape, optical disk, or some other secondary storage device. A database consists of a file or a set of files. The information in t
3、he these files may be broken down into records, each of which consists of one or more fields are the basic units of data storage, and each field typically contains information pertaining to one aspect or attribute of the entity described by the database. Using keywords and various sorting commands,
4、users can rapidly search, rearrange, group, and select the fields in many records to retrieve or create reports on particular aggregates of data. Database records and files must be organized to allow retrieval of the information. Early system were arranged sequentially (i.e., alphabetically, numeric
5、ally, or chronologically)； the development of direct-access storage devices made possible random access to data via indexes. Queries are the main way users retrieve database information. Typically the user provides a string of characters, and the computer searches the database for a corresponding se
6、quence and provides the source materials in which those characters appear. A user can request, for example, all records in which the content of the field for a persons last name is the word Smith.The many users of a large database must be able to manipulate the information within it quickly at any g
7、iven time. Moreover, large business and other organizations tend to build up many independent files containing related and even overlapping data, and their data, processing activities often require the linking of data from several files. Several different types of database management systems have be
8、en developed to support these requirements: flat, hierarchical, network, relational, and object-oriented. In flat databases, records are organized according to a simple list of entities； many simple databases for personal computers are flat in structure. The records in hierarchical databases are org
9、anized in a treelike structure, with each level of records branching off into a set of smaller categories. Unlike hierarchical databases, which provide single links between sets of records at different levels, network databases create multiple linkages between sets by placing links, or pointers, to
10、one set of records in another； the speed and versatility of network databases have led to their wide use in business. Relational databases are used where associations among files or records cannot be expressed by links； a simple flat list becomes one table, or “relation”, and multiple relations can
11、be mathematically associated to yield desired information. Object-oriented databases store and manipulate more complex data structures, called “objects”, which are organized into hierarchical classes that may inherit properties from classes higher in the chain； this database structure is the most fl
12、exible and adaptable. The information in many databases consists of natural-language texts of documents； number-oriented database primarily contain information such as statistics, tables, financial data, and raw scientific and technical data. Small databases can be maintained on personal-computer sy
13、stems and may be used by individuals at home. These and larger databases have become increasingly 计算机与信息学院 本科毕业设计（论文） - 2 - important in business life. Typical commercial applications include airline reservations, production management, medical records in hospitals, and legal records of insurance co
14、mpanies. The largest databases are usually maintained by governmental agencies, business organizations, and universities. These databases may contain texts of such materials as catalogs of various kinds. Reference databases contain bibliographies or indexes that serve as guides to the location of in
15、formation in books, periodicals, and other published literature. Thousands of these publicly accessible databases now exist, covering topics ranging from law, medicine, and engineering to news and current events, games, classified advertisements, and instructional courses. Professionals such as scie
16、ntists, doctors, lawyers, financial analysts, stockbrokers, and researchers of all types increasingly rely on these databases for quick, selective access to large volumes of information. DBMS Structuring Techniques Sequential, direct, and other file processing approaches are used to organize and str
17、ucture data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquiries for information. That is, the DBMS is able to structure and tie together the logically related data from several large files. Logical Structures. Identifying these logical
18、relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations. List structures. In this logical approach, records are linked together
19、by the use of pointers. A pointer is a data item in one record that identifies the storage location of another logically related record. Records in a customer master file, for example, will contain the name and address of each customer, and each record in this file is identified by an account number
20、. During an accounting period, a customer may buy a number of items on different days. Thus, the company may maintain an invoice file to reflect these transactions. A list structure could be used in this situation to show the unpaid invoices at any given time. Each record in the customer in the invo
21、ice file. This invoice record, in turn, would be linked to later invoices for the customer. The last invoice in the chain would be identified by the use of a special character as a pointer. Hierarchical (tree) structures. In this logical approach, data units are structured in multiple levels that gr
22、aphically resemble an “upside down” tree with the root at the top and the branches formed below. Theres a superior-subordinate relationship in a hierarchical (tree) structure. Below the single-root data component are subordinate elements or nodes, each of which, in turn, “own” one or more other elem
23、ents (or none). Each element or branch in this structure below the root has only a single owner. Thus, a customer owns an invoice, and the invoice has subordinate items. The branches in a tree structure are not connected. Network Structures. Unlike the tree approach, which does not permit the connec
24、tion of branches, the network structure permits the connection of the nodes in a multidirectional manner. Thus, each node may have several owners and may, in turn, own any number of other data units. Data management software permits the extraction of the needed information from such a structure by b
25、eginning with any record in a file. Relational structures. A relational structure is made up of many tables. The data are stored in the form of “relations” in these tables. For example, relation tables could be established to link a college course with the instructor of the course, and with the loca
26、tion of the class. To find the name of the instructor and the location of the English class, the course/instructor relation is searched to get the name (“Fitt”), and the course/location relation is a relatively new database structuring approach 计算机与信息学院 本科毕业设计（论文） - 3 - thats expected to be widely i
27、mplemented in the future. Physical Structures. People visualize or structure data in logical ways for their own purposes. Thus, records R1 and R2 may always be logically linked and processed in sequence in one particular application. However, in a computer system its quite possible that these record
28、s that are logically contiguous in one application are not physically stored together. Rather, the physical structure of the records in media and hardware may depend not only on the I/O and storage devices and techniques used, but also on the different logical relationships that users may assign to
29、the data found in R1and R2. For example, R1 and R2 may be records of credit customers who have shipments send to the same block in the same city every 2 weeks. From the shipping department managers perspective, then, R1 and R2 are sequential entries on a geographically organized shipping report. But
30、 in the A/R application, the customers represented by R1 and R2 may be identified, and their accounts may be processed, according to their account numbers which are widely separated. In short, then, the physical location of the stored records in many computer-based information systems is invisible t
31、o users. Database Management Features of Oracle Oracle includes many features that make the database easier to manage. Weve divided the discussion in this section into three categories: Oracle Enterprise Manager, add-on packs, backup and recovery. Oracle Enterprise Manager As part of every Database
32、Server, Oracle provides the Oracle Enterprise Manager (EM), a database management tool framework with a graphical interface used to manage database users, instances, and features (such as replication) that can provide additional information about the Oracle environment. Prior to the Oracle8i databas
33、e, the EM software had to be installed on Windows 95/98 or NT-based systems and each repository could be accessed by only a single database manager at a time. Now you can use EM from a browser or load it onto Windows 95/98/2000 or NT-based systems. Multiple database administrators can access the EM
34、repository at the same time. In the EM repository for Oracle9i, the super administrator can define services that should be displayed on other administrators consoles, and management regions can be set up. Add-on packs Several optional add-on packs are available for Oracle, as described in the follow
35、ing sections. In addition to these database-management packs, management packs are available for Oracle Applications and for SAP R/3. (一 ) standard Management Pack The Standard Management Pack for Oracle provides tools for the management of small Oracle databases (e.g., Oracle Server/Standard Editio
36、n). Features include support for performance monitoring of database contention, I/O, load, memory use and instance metrics, session analysis, index tuning, and change investigation and tracking. (二 ) Diagnostics Pack You can use the Diagnostic Pack to monitor, diagnose, and maintain the health of Enterprise Edition databases, operating systems, and applications. With both historical and real-time analysis, you can automatically avoid problems before they occur. The pack also provides capacity planning features that help you plan and track future system-resource requirements. (三 ) Tuning Pack
