高级数据库系统第一章简介.ppt

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1、Database System Concepts,5th Ed.Silberschatz,Korth and SudarshanSee www.db- for conditions on re-use Chapter 1:IntroductionSilberschatz,Korth and Sudarshan1.2Database System Concepts-5th Edition,May 23,2005Chapter 1:IntroductionnPurpose of Database SystemsnDatabase LanguagesnRelational DatabasesnDat

2、abase DesignnData ModelsnDatabase InternalsnDatabase Users and AdministratorsnOverall StructurenHistory of Database SystemsSilberschatz,Korth and Sudarshan1.3Database System Concepts-5th Edition,May 23,2005Database Management System(DBMS)nDBMS contains information about a particular enterpriselColle

3、ction of interrelated datalSet of programs to access the data lAn environment that is both convenient and efficient to usenDatabase Applications:lBanking:all transactionslAirlines:reservations,scheduleslUniversities:registration,gradeslSales:customers,products,purchaseslOnline retailers:order tracki

4、ng,customized recommendationslManufacturing:production,inventory,orders,supply chainlHuman resources:employee records,salaries,tax deductionsnDatabases touch all aspects of our livesSilberschatz,Korth and Sudarshan1.4Database System Concepts-5th Edition,May 23,2005Purpose of Database SystemsnIn the

5、early days,database applications were built directly on top of file systemsnDrawbacks of using file systems to store data:lData redundancy and inconsistency4Multiple file formats,duplication of information in different fileslDifficulty in accessing data 4Need to write a new program to carry out each

6、 new tasklData isolation multiple files and formatslIntegrity problems4Integrity constraints (e.g.account balance 0)become“buried”in program code rather than being stated explicitly4Hard to add new constraints or change existing onesSilberschatz,Korth and Sudarshan1.5Database System Concepts-5th Edi

7、tion,May 23,2005Purpose of Database Systems(Cont.)nDrawbacks of using file systems(cont.)lAtomicity of updates4Failures may leave database in an inconsistent state with partial updates carried out4Example:Transfer of funds from one account to another should either complete or not happen at alllConcu

8、rrent access by multiple users4Concurrent accessed needed for performance4Uncontrolled concurrent accesses can lead to inconsistenciesExample:Two people reading a balance and updating it at the same timelSecurity problems4Hard to provide user access to some,but not all,datanDatabase systems offer so

9、lutions to all the above problemsSilberschatz,Korth and Sudarshan1.6Database System Concepts-5th Edition,May 23,2005Levels of AbstractionnPhysical level:describes how a record(e.g.,customer)is stored.nLogical level:describes data stored in database,and the relationships among the data.type customer=

10、recordcustomer_id:string;customer_name:string;customer_street:string;customer_city:string;end;nView level:application programs hide details of data types.Views can also hide information(such as an employees salary)for security purposes.Silberschatz,Korth and Sudarshan1.7Database System Concepts-5th

11、Edition,May 23,2005View of DataAn architecture for a database system Silberschatz,Korth and Sudarshan1.8Database System Concepts-5th Edition,May 23,2005Instances and SchemasnSimilar to types and variables in programming languagesnSchema the logical structure of the database lExample:The database con

12、sists of information about a set of customers and accounts and the relationship between them)lAnalogous to type information of a variable in a programlPhysical schema:database design at the physical levellLogical schema:database design at the logical levelnInstance the actual content of the database

13、 at a particular point in time lAnalogous to the value of a variablenPhysical Data Independence the ability to modify the physical schema without changing the logical schemalApplications depend on the logical schemalIn general,the interfaces between the various levels and components should be well d

14、efined so that changes in some parts do not seriously influence others.Silberschatz,Korth and Sudarshan1.9Database System Concepts-5th Edition,May 23,2005Data ModelsnA collection of tools for describing lData lData relationshipslData semanticslData constraintsnRelational modelnEntity-Relationship da

15、ta model(mainly for database design)nObject-based data models(Object-oriented and Object-relational)nSemistructured data model (XML)nOther older models:lNetwork model lHierarchical modelSilberschatz,Korth and Sudarshan1.10Database System Concepts-5th Edition,May 23,2005Data Manipulation Language(DML

16、)nLanguage for accessing and manipulating the data organized by the appropriate data modellDML also known as query languagenTwo classes of languages lProcedural user specifies what data is required and how to get those data lDeclarative(nonprocedural)user specifies what data is required without spec

17、ifying how to get those datanSQL is the most widely used query languageSilberschatz,Korth and Sudarshan1.11Database System Concepts-5th Edition,May 23,2005Data Definition Language(DDL)nSpecification notation for defining the database schemaExample:create table account(account_number char(10),branch_

18、name char(10),balance integer)nDDL compiler generates a set of tables stored in a data dictionarynData dictionary contains metadata(i.e.,data about data)lDatabase schema lData storage and definition language 4Specifies the storage structure and access methods usedlIntegrity constraints4Domain constr

19、aints4Referential integrity(e.g.branch_name must correspond to a valid branch in the branch table)lAuthorizationSilberschatz,Korth and Sudarshan1.12Database System Concepts-5th Edition,May 23,2005Relational ModelnExample of tabular data in the relational modelAttributesSilberschatz,Korth and Sudarsh

20、an1.13Database System Concepts-5th Edition,May 23,2005A Sample Relational DatabaseSilberschatz,Korth and Sudarshan1.14Database System Concepts-5th Edition,May 23,2005SQLnSQL:widely used non-procedural languagelExample:Find the name of the customer with customer-id 192-83-7465selectcustomer.customer_

21、namefromcustomerwherecustomer.customer_id=192-83-7465lExample:Find the balances of all accounts held by the customer with customer-id 192-83-7465selectaccount.balancefrom depositor,accountwhere depositor.customer_id=192-83-7465 anddepositor.account_number=account.account_numbernApplication programs

22、generally access databases through one oflLanguage extensions to allow embedded SQLlApplication program interface(e.g.,ODBC/JDBC)which allow SQL queries to be sent to a databaseSilberschatz,Korth and Sudarshan1.15Database System Concepts-5th Edition,May 23,2005Database DesignThe process of designing

23、 the general structure of the database:nLogical Design Deciding on the database schema.Database design requires that we find a“good”collection of relation schemas.lBusiness decision What attributes should we record in the database?lComputer Science decision What relation schemas should we have and h

24、ow should the attributes be distributed among the various relation schemas?nPhysical Design Deciding on the physical layout of the database Silberschatz,Korth and Sudarshan1.16Database System Concepts-5th Edition,May 23,2005The Entity-Relationship ModelnModels an enterprise as a collection of entiti

25、es and relationshipslEntity:a“thing”or“object”in the enterprise that is distinguishable from other objects4Described by a set of attributeslRelationship:an association among several entitiesnRepresented diagrammatically by an entity-relationship diagram:Silberschatz,Korth and Sudarshan1.17Database S

26、ystem Concepts-5th Edition,May 23,2005Other Data ModelsnObject-oriented data modelnObject-relational data modelSilberschatz,Korth and Sudarshan1.18Database System Concepts-5th Edition,May 23,2005Database Application Architectures(web browser)OldModernSilberschatz,Korth and Sudarshan1.19Database Syst

27、em Concepts-5th Edition,May 23,2005Database Management System InternalsnStorage managementnQuery processingnTransaction processingSilberschatz,Korth and Sudarshan1.20Database System Concepts-5th Edition,May 23,2005Storage ManagementnStorage manager is a program module that provides the interface bet

28、ween the low-level data stored in the database and the application programs and queries submitted to the system.nThe storage manager is responsible to the following tasks:lInteraction with the file manager lEfficient storing,retrieving and updating of datanIssues:lStorage accesslFile organizationlIn

29、dexing and hashingSilberschatz,Korth and Sudarshan1.21Database System Concepts-5th Edition,May 23,2005Query Processing1.Parsing and translation2.Optimization3.EvaluationSilberschatz,Korth and Sudarshan1.22Database System Concepts-5th Edition,May 23,2005Query Processing(Cont.)nAlternative ways of eva

30、luating a given querylEquivalent expressionslDifferent algorithms for each operationnCost difference between a good and a bad way of evaluating a query can be enormousnNeed to estimate the cost of operationslDepends critically on statistical information about relations which the database must mainta

31、inlNeed to estimate statistics for intermediate results to compute cost of complex expressionsSilberschatz,Korth and Sudarshan1.23Database System Concepts-5th Edition,May 23,2005Transaction ManagementnA transaction is a collection of operations that performs a single logical function in a database a

32、pplicationnTransaction-management component ensures that the database remains in a consistent(correct)state despite system failures(e.g.,power failures and operating system crashes)and transaction failures.nConcurrency-control manager controls the interaction among the concurrent transactions,to ens

33、ure the consistency of the database.Silberschatz,Korth and Sudarshan1.24Database System Concepts-5th Edition,May 23,2005Overall System Structure Silberschatz,Korth and Sudarshan1.25Database System Concepts-5th Edition,May 23,2005History of Database Systemsn1950s and early 1960s:lData processing usin

34、g magnetic tapes for storage4Tapes provide only sequential accesslPunched cards for inputnLate 1960s and 1970s:lHard disks allow direct access to datalNetwork and hierarchical data models in widespread uselTed Codd defines the relational data model4Would win the ACM Turing Award for this work4IBM Re

35、search begins System R prototype4UC Berkeley begins Ingres prototypelHigh-performance(for the era)transaction processingSilberschatz,Korth and Sudarshan1.26Database System Concepts-5th Edition,May 23,2005History(cont.)n1980s:lResearch relational prototypes evolve into commercial systems4SQL becomes

36、industry standardlParallel and distributed database systemslObject-oriented database systemsn1990s:lLarge decision support and data-mining applicationslLarge multi-terabyte data warehouseslEmergence of Web commercen2000s:lXML and XQuery standardslAutomated database administrationlIncreasing use of h

37、ighly parallel database systemslWeb-scale distributed data storage systemsDatabase System Concepts,5th Ed.Silberschatz,Korth and SudarshanSee www.db- for conditions on re-use End of Chapter 1Silberschatz,Korth and Sudarshan1.28Database System Concepts-5th Edition,May 23,2005Database UsersUsers are d

38、ifferentiated by the way they expect to interact with the systemnApplication programmers interact with system through DML callsnSophisticated users form requests in a database query languagenSpecialized users write specialized database applications that do not fit into the traditional data processin

39、g frameworknNave users invoke one of the permanent application programs that have been written previouslylExamples,people accessing database over the web,bank tellers,clerical staffSilberschatz,Korth and Sudarshan1.29Database System Concepts-5th Edition,May 23,2005Database AdministratornCoordinates

40、all the activities of the database systemlhas a good understanding of the enterprises information resources and needs.nDatabase administrators duties include:lStorage structure and access method definitionlSchema and physical organization modificationlGranting users authority to access the databasel

41、Backing up datalMonitoring performance and responding to changes4Database tuningSilberschatz,Korth and Sudarshan1.30Database System Concepts-5th Edition,May 23,2005Database ArchitectureThe architecture of a database systems is greatly influenced by the underlying computer system on which the databas

42、e is running:nCentralizednClient-servernParallel(multiple processors and disks)nDistributed Silberschatz,Korth and Sudarshan1.31Database System Concepts-5th Edition,May 23,2005Object-Relational Data ModelsnExtend the relational data model by including object orientation and constructs to deal with a

43、dded data types.nAllow attributes of tuples to have complex types,including non-atomic values such as nested relations.nPreserve relational foundations,in particular the declarative access to data,while extending modeling power.nProvide upward compatibility with existing relational languages.Silbers

44、chatz,Korth and Sudarshan1.32Database System Concepts-5th Edition,May 23,2005XML:Extensible Markup LanguagenDefined by the WWW Consortium(W3C)nOriginally intended as a document markup language not a database languagenThe ability to specify new tags,and to create nested tag structures made XML a grea

45、t way to exchange data,not just documentsnXML has become the basis for all new generation data interchange formats.nA wide variety of tools is available for parsing,browsing and querying XML documents/dataSilberschatz,Korth and Sudarshan1.33Database System Concepts-5th Edition,May 23,2005Figure 1.4Silberschatz,Korth and Sudarshan1.34Database System Concepts-5th Edition,May 23,2005Figure 1.7