山大數(shù)據(jù)庫(kù)系統(tǒng)英語課件01緒論

1、Chapter 1: Introduction Database Management System (DBMS)DBMS contains information about a particular enterpriseCollection of interrelated dataSet of programs to access the data An environment that is both convenient and efficient to useDatabase Applications:Banking: transactionsAirlines: reservatio

2、ns, schedulesUniversities: registration, gradesSales: customers, products, purchasesOnline retailers: order tracking, customized recommendationsManufacturing: production, inventory, orders, supply chainHuman resources: employee records, salaries, tax deductionsDatabases can be very large.Databases t

3、ouch all aspects of our livesUniversity Database ExampleApplication program examplesAdd new students, instructors, and coursesRegister students for courses, and generate class rostersAssign grades to students, compute grade point averages (GPA) and generate transcriptsIn the early days, database app

4、lications were built directly on top of file systemsDrawbacks of using file systems to store dataData redundancy and inconsistencyMultiple file formats, duplication of information in different filesDifficulty in accessing data Need to write a new program to carry out each new taskData isolation mult

5、iple files and formatsIntegrity problemsIntegrity constraints (e.g., account balance 0) become “buried” in program code rather than being stated explicitlyHard to add new constraints or change existing onesDrawbacks of using file systems to store data (Cont.)Atomicity of updatesFailures may leave da

6、tabase in an inconsistent state with partial updates carried outExample: Transfer of funds from one account to another should either complete or not happen at allConcurrent access by multiple usersConcurrent access needed for performanceUncontrolled concurrent accesses can lead to inconsistenciesExa

7、mple: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same timeSecurity problemsHard to provide user access to some, but not all, dataDatabase systems offer solutions to all the above problemsLevels of AbstractionPhysical level: describes how a record

8、 (e.g., customer) is stored.Logical level: describes data stored in database, and the relationships among the data.type instructor = recordID : string; name : string;dept_name : string;salary : integer;end;View level: application programs hide details of data types. Views can also hide information (

9、such as an employees salary) for security purposes. View of DataAn architecture for a database system Instances and SchemasSimilar to types and variables in programming languagesSchema the logical structure of the database Example: The database consists of information about a set of customers and ac

10、counts and the relationship between themAnalogous to type information of a variable in a programPhysical schema: database design at the physical levelLogical schema: database design at the logical levelInstance the actual content of the database at a particular point in time Analogous to the value o

11、f a variablePhysical Data Independence the ability to modify the physical schema without changing the logical schemaApplications depend on the logical schemaIn general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously infl

12、uence others.Data ModelsA collection of tools for describing Data Data relationshipsData semanticsData constraintsRelational modelEntity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Object-relational)Semistructured data model (XML)Other older mod

13、els:Network model Hierarchical modelRelational ModelRelational model (Chapter 2)Example of tabular data in the relational modelColumnsRowsA Sample Relational DatabaseData Manipulation Language (DML)Language for accessing and manipulating the data organized by the appropriate data modelDML also known

14、 as query languageTwo classes of languages Procedural user specifies what data is required and how to get those data Declarative (nonprocedural) user specifies what data is required without specifying how to get those dataSQL is the most widely used query languageData Definition Language (DDL)Specif

15、ication notation for defining the database schemaExample:create table instructor ( ID char(5), name varchar(20), dept_name varchar(20), salary numeric(8,2)DDL compiler generates a set of table templates stored in a data dictionaryData dictionary contains metadata (i.e., data about data)Database sche

16、ma Integrity constraintsPrimary key (ID uniquely identifies instructors)Referential integrity (references constraint in SQL)e.g. dept_name value in any instructor tuple must appear in department relationAuthorizationSQLSQL: widely used non-procedural languageExample: Find the name of the instructor

17、with ID 22222selectnamefrominstructorwhereinstructor.ID = 22222Example: Find the ID and building of instructors in the Physics dept. select instructor.ID, department.buildingfrom instructor, departmentwhere instructor.dept_name = department.dept_name and department.dept_name = Physics Application pr

18、ograms generally access databases through one ofLanguage extensions to allow embedded SQLApplication program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a databaseChapters 3, 4 and 5Database DesignThe process of designing the general structure of the database:Logical Design Dec

19、iding on the database schema. Database design requires that we find a “good” collection of relation schemas.Business decision What attributes should we record in the database?Computer Science decision What relation schemas should we have and how should the attributes be distributed among the various

20、 relation schemas?Physical Design Deciding on the physical layout of the database Database Design?Is there any problem with this design?Design ApproachesNormalization Theory (Chapter 8)Formalize what designs are bad, and test for themEntity Relationship Model (Chapter 7)Models an enterprise as a col

21、lection of entities and relationshipsEntity: a “thing” or “object” in the enterprise that is distinguishable from other objectsDescribed by a set of attributesRelationship: an association among several entitiesRepresented diagrammatically by an entity-relationship diagram:The Entity-Relationship Mod

22、elModels an enterprise as a collection of entities and relationshipsEntity: a “thing” or “object” in the enterprise that is distinguishable from other objectsDescribed by a set of attributesRelationship: an association among several entitiesRepresented diagrammatically by an entity-relationship diag

23、ram:What happened to dept_name of instructor and student?Object-Relational Data ModelsRelational model: flat, “atomic” valuesObject Relational Data ModelsExtend the relational data model by including object orientation and constructs to deal with added data types.Allow attributes of tuples to have c

24、omplex types, including non-atomic values such as nested relations.Preserve relational foundations, in particular the declarative access to data, while extending modeling power.Provide upward compatibility with existing relational languages.XML: Extensible Markup LanguageDefined by the WWW Consortiu

25、m (W3C)Originally intended as a document markup language not a database languageThe ability to specify new tags, and to create nested tag structures made XML a great way to exchange data, not just documentsXML has become the basis for all new generation data interchange formats.A wide variety of too

26、ls is available for parsing, browsing and querying XML documents/dataStorage ManagementStorage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.The storage manager is responsible

27、 to the following tasks: Interaction with the file manager Efficient storing, retrieving and updating of dataIssues:Storage accessFile organizationIndexing and hashingQuery Processing1.Parsing and translation2.Optimization3.EvaluationQuery Processing (Cont.)Alternative ways of evaluating a given que

28、ryEquivalent expressionsDifferent algorithms for each operationCost difference between a good and a bad way of evaluating a query can be enormousNeed to estimate the cost of operationsDepends critically on statistical information about relations which the database must maintainNeed to estimate stati

29、stics for intermediate results to compute cost of complex expressionsTransaction ManagementWhat if the system fails?What if more than one user is concurrently updating the same data?A transaction is a collection of operations that performs a single logical function in a database applicationTransacti

30、on-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.Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database. Database Users and AdministratorsDatabaseDatabase System InternalsDatabase ArchitectureThe architecture of a database systems is greatly influenced by the underlying computer system on which the database is running:CentralizedClient