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1、计算机与信息学院本科毕业设计（论文）外文资料翻译外文资料翻译-原文部分原文部分Database ManagementDatabase Management(From http：/wenku.baidu。com/view/51857f07cc17552707220879.html，2011）Database(sometimes spelled database）is also called an electronic database,referring to anycollections of data,or information,that is specially organized fo
2、r rapid search and retrieval by acomputer.Databases are structured to facilitate the storage，retrieval modification and deletion ofdata in conjunction with various dataprocessing operations。Database can be stored on magneticdisk or tape，optical disk,or some other secondary storage device。A database
3、consists of a file or a set of files。The information in the these files may be brokendown 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 entitydescribed by the da
4、tabase。Using keywords and various sorting commands,users can rapidlysearch，rearrange,group，and select the fields in many records to retrieve or create reports onparticular aggregates of data。Database records and files must be organized to allow retrieval of the information.Early systemwere arranged
5、sequentially(i.e.,alphabetically，numerically,or chronologically）；the developmentof direct-access storage devices made possible random access to data via indexes.Queries are themain way users retrieve database information.Typically the user provides a string of characters，and the computer searches th
6、e database for a corresponding sequence and provides the sourcematerials in which those characters appear。A user can request，for example,all records in whichthe content of the field for a persons last name is the word Smith。The many users of a largedatabase must be able to manipulate the information
7、 within it quickly at any given time。Moreover，large business and other organizations tend to build up many independent files containing relatedand even overlapping data，and their data，processing activities often require the linking of datafrom several files.Several different types of database manage
8、ment systems have been developed tosupport these requirements：flat,hierarchical，network,relational,and object-oriented。In flat databases，records are organized according to a simple list of entities；many simpledatabases for personal computers are flat in structure.The records in hierarchical database
9、s areorganized in a treelike structure，with each level of records branching off into a set of smallercategories.Unlike hierarchical databases,which provide single links between sets of records atdifferent levels,network databases create multiple linkages between sets by placing links，orpointers，to o
10、ne set of records in another；the speed and versatility of network databases have ledto their wide use in business.Relational databases are used where associations among files orrecords cannot be expressed by links;a simple flat list becomes one table，or“relation”，andmultiple relations can be mathema
11、tically associated to yield desired information.Objectorienteddatabases store and manipulate more complex data structures,called“objects,which are organizedinto hierarchical classes that may inherit properties from classes higher in the chain；this databasestructure is the most flexible and adaptable
12、。The information in many databases consists of naturallanguage texts of documents；numberoriented database primarily contain information such as statistics,tables，financial data，and raw scientific and technical data.Small databases can be maintained on personal-computersystems and may be used by indi
13、viduals at home.These and larger databases have become-1-计算机与信息学院本科毕业设计（论文）increasingly important in business life.Typical commercial applications include airline reservations，production management,medical records in hospitals,and legal records of insurance companies.Thelargest databases are usually
14、 maintained by governmental agencies，business organizations,anduniversities.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 ofinformation in books，periodicals，and other publish
15、ed literature。Thousands of these publiclyaccessible databases now exist，covering topics ranging from law，medicine，and engineering tonews and current events,games，classified advertisements，and instructional courses.Professionalssuch as scientists，doctors，lawyers,financial analysts，stockbrokers,and re
16、searchers of all typesincreasingly rely on these databases for quick，selective access to large volumes of information.DBMS Structuring TechniquesSequential,direct，and other file processing approaches are used to organize and structure datain single files。But a DBMS is able to integrate data elements
17、 from several files to answer specificuser inquiries for information。That is，the DBMS is able to structure and tie together the logicallyrelated data from several large files。Logical Structures.Identifying these logical relationships is a job of the data administrator。Adata definition language is us
18、ed for this purpose.The DBMS may then employ one of the followinglogical structuring techniques during storage access，and retrieval operations。List structures.In this logical approach，records are linked together by the use of pointers。Apointer is a data item in one record that identifies the storage
19、 location of another logically relatedrecord.Records in a customer master file，for example,will contain the name and address of eachcustomer,and each record in this file is identified by an account number。During an accountingperiod，a customer may buy a number of items on different days.Thus，the comp
20、any may maintainan invoice file to reflect these transactions.A list structure could be used in this situation to show theunpaid invoices at any given time.Each record in the customer in the invoice file.This invoicerecord，in turn，would be linked to later invoices for the customer。The last invoice i
21、n the chainwould be identified by the use of a special character as a pointer.Hierarchical（tree）structures。In this logical approach，data units are structured in multiplelevels that graphically resemble an“upside down”tree with the root at the top and the branchesformed below。Theres a superiorsubordi
22、nate relationship in a hierarchical(tree)structure.Belowthe single-root data component are subordinate elements or nodes,each of which,in turn，“own”one or more other elements（or none)。Each element or branch in this structure below the root hasonly a single owner。Thus，a customer owns an invoice，and t
23、he invoice has subordinate items.The branches in a tree structure are not connected.Network Structures。Unlike the tree approach，which does not permit the connection ofbranches，the network structure permits the connection of the nodes in a multidirectional manner.Thus，each node may have several owner
24、s 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 bybeginning with any record in a file.Relational structures.A relational structure is made up of many tables。The data are stored inthe form of“relation
25、s”in these tables.For example,relation tables could be established to link acollege course with the instructor of the course,and with the location of the class.To find the nameof the instructor and the location of the English class,the course/instructor relation is searched to getthe name（“Fitt”），an
26、d the course/location relation is a relatively new database structuring-2-计算机与信息学院本科毕业设计（论文）approach thats expected to be widely implemented 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 link
27、ed and processed in sequence in one particularapplication.However，in a computer system its quite possible that these records that are logicallycontiguous in one application are not physically stored together。Rather,the physical structure ofthe records in media and hardware may depend not only on the
28、 I/O and storage devices andtechniques used，but also on the different logical relationships that users may assign to the datafound in R1and R2。For example,R1 and R2 may be records of credit customers who haveshipments send to the same block in the same city every 2 weeks.From the shipping department
29、managers perspective,then,R1 and R2 are sequential entries on a geographically organizedshipping report。But in the A/R application,the customers represented by R1 and R2 may beidentified，and their accounts may be processed，according to their account numbers which arewidely separated.In short，then,th
30、e physical location of the stored records in manycomputerbased information systems is invisible to users。Database Management Features of OracleDatabase Management Features of OracleOracle includes many features that make the database easier to manage.Weve divided thediscussion in this section into t
31、hree categories:Oracle Enterprise Manager，addon packs,backupand recovery.Oracle Enterprise ManagerOracle Enterprise ManagerAs part of every Database Server,Oracle provides the Oracle Enterprise Manager（EM），adatabase management tool framework with a graphical interface used to manage database users,i
32、nstances,and features（such as replication）that can provide additional information about theOracle environment.Prior to the Oracle8i database，the EM software had to be installed on Windows 95/98 orNTbased systems and each repository could be accessed by only a single database manager at atime.Now you
33、 can use EM from a browser or load it onto Windows 95/98/2000 or NT-basedsystems。Multiple database administrators can access the EM repository at the same time.In theEM repository for Oracle9i,the super administrator can define services that should be displayed onother administrators consoles，and ma
34、nagement regions can be set up。AddAddon packson packsSeveral optional addon packs are available for Oracle，as described in the following sections.In addition to these database-management packs,management packs are available for OracleApplications and for SAP R/3。(一)standard Management PackThe Standa
35、rd Management Pack for Oracle provides tools for the management of small Oracledatabases(e。g.，Oracle Server/Standard Edition）.Features include support for performancemonitoring of database contention,I/O，load，memory use and instance metrics,session analysis,index tuning,and change investigation and
36、tracking.(二)Diagnostics PackYou can use the Diagnostic Pack to monitor，diagnose，and maintain the health ofEnterprise Edition databases,operating systems,and applications.With both historical and real-timeanalysis，you can automatically avoid problems before they occur.The pack also provides capacityp
37、lanning features that help you plan and track future system-resource requirements.(三)Tuning Pack-3-计算机与信息学院本科毕业设计（论文）With the Tuning Pack，you can optimise system performance by identifying and tuningEnterprise Edition databases and application bottlenecks such as inefficient SQL,poor data design,and
38、 the improper use of system resources.The pack can proactively discover tuning opportunitiesand automatically generate the analysis and required changes to tune the systems.(四)Change Management PackThe Change Management Pack helps eliminate errors and loss of data when upgradingEnterprise Edition da
39、tabases to support new applications.It impact and complex dependenciesassociated with application changes and automatically perform database upgrades。Users caninitiate changes with easy-touse wizards that teach the systematic steps necessary to upgrade。(五)AvailabilityOracle Enterprise Manager can be
40、 used for managing Oracle Standard Edition and/or EnterpriseEdition.Additional functionality is provided by separate Diagnostics,Tuning，and ChangeManagement Packs。Backup and RecoveryBackup and RecoveryAs every database administrator knows,backing up a database is a rather mundane butnecessary task.A
41、n improper backup makes recovery difficult，if not impossible.Unfortunately,people often realize the extreme importance of this everyday task only when it is too lateusuallyafter losing businesscritical data due to a failure of a related system。The following sections describe some products and techni
42、ques for performing database backupoperations。1)Recovery ManagerTypical backups include complete database backups（the most common type）,databasebackups,control file backups，and recovery of the database。Previously，Oracles EnterpriseBackup Utility(EBU）provided a similar solution on some platforms。Howe
43、ver,RMAN，with itsRecovery Catalog stored in an Oracle database,provides a much more complete solution.RMANcan automatically locate,back up,restore,and recover databases,control files，and archived redologs.RMAN for Oracle9i can restart backups and restores and implement recovery window policieswhen b
44、ackups expire.The Oracle Enterprise Manager Backup Manager provides a GUI-basedinterface to RMAN.2)Incremental backup and recoveryRMAN can perform incremental backups of Enterprise Edition databases.Incremental backupsback up only the blocks modified since the last backup of a datafile，tablespace,or
45、 database;thus,theyre smaller and faster than complete backups.RMAN can also perform point-intime recovery,which allows the recovery of data until just prior to a undesirable event.3)Legato Storage ManagerVarious media-management software vendors support RMAN。Oracle bundles Legato StorageManager wit
46、h Oracle to provide mediamanagement services,including the tracking of tapevolumes,for up to four devices。RMAN interfaces automatically with the mediamanagementsoftware to request the mounting of tapes as needed for backup and recovery operations.4)AvailabilityWhile basic recovery facilities are ava
47、ilable for both Oracle Standard Edition and EnterpriseEdition,incremental backups have typically been limited to Enterprise Edition.Choosing between Oracle and SQL ServerChoosing between Oracle and SQL ServerI have to decide between using the Oracle database and WebDB vs。Microsoft SQL Server-4-计算机与信
48、息学院本科毕业设计（论文）with Visual Studio。This choice will guide our future Web projects。What are the strong points ofeach of these combinations and what are the negatives?Lori:Making your decision will depend on what you already have。For instance,if you want toimplement a Webbased database application and yo
49、u are a Windows-only shop,SQL Server andthe Visual Studio package would be fine。But the Oracle solution would be better with mixedplatforms。There are other things to consider，such as what extras you get and what skills are required.WebDB is a content management and development tool that can be used
50、by content creators，database administrators，and developers without any programming experience.WebDB is abrowserbased tool that helps ease content creation and provides monitoring and maintenancetools。This is a good solution for organizations already using Oracle.Oracle also scales better thanSQL Ser