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1、四 级 数 据 库 重 点 难 点 分 析(Four level database,key and difficultanalysis)Computer four level examination:four level database key anddifficult analysis(Part one)Introduction1.data is a symbolic record of real-world things,aninformation that can be recorded with physical symbols.Data is the symbolic repres
2、entation of information,and is thecarrier;information is the semantic interpretation of data,and it is the connotation.The 2.is the data model of the real world data abstraction,is the formal framework of database system,a set of conceptsand definitions used to describe the data,including datadescri
3、ption,data 1 ink,data manipulation,data semantics anddata consistency concept tool.Satisfy three conditions:simulate the real world morerealistically;easy to understand;easy to realize by computerThree elements:data structure(static link,data structure andthe object itself),data manipulation(a colle
4、ction of dataobjects and operation rules)and integrity constraints(semantic constraints:data model,data within and betweencontact)The 3.model is a description of the logical structure andcharacteristics of all data in the database,a common data viewof al 1 users,also known as logical or conceptual p
5、atterns.Outside the model is the logical structure and characteristicsof local data can see and use the database user description,is associated with a data application logic representation,also known as sub mode,user mode or user view.An internal schema is a description of the physical structureand
6、storage of data in a database,also known as physical orstorage patterns.When the database schema changes,the relationship betweenimage by adjusting the external mode/pattern between theapplications that need not be changed,so as to ensure thelogical data independence between application programs and
7、 thelogical data independenceWhen changing the physical storage structure of database data,by adjusting the model/schema mapping relationship,keep thedatabase model unchanged,the pattern and the application ofthe database system is not changed,ensure the physical dataindependence between application
8、 programs and the physicaldata independence”.4.database is a set of shared data stored in computer,anddatabase management system is a kind of data management systemsoftware.The database system is the software and hardwaresystem after the introduction of the database in the computersystem.It includes
9、 the database,database management systemand database application program.The main functions of 5.DBMS include data definition,datamanipulation,database operation,management and control,database establishment and maintenance.DBMS includes query processor and storage manager.Queryprocessor implements
10、user oriented query,analysis,processingand optimization functions.The storage manager providesinterfaces for users and applications to access the applicationdata stored in the database file.6.models with two-dimensional surface representation betweenthe entity and the entity relation,each object in
11、the realworld corresponds to a row in a table is called a record of eachcolumn in the table(attribute)describe a character class,thevalue of the column(attribute value)described a specificobjective the features of the objects.The advantages and disadvantages:the establishment of theset relationship”
12、,the concept of strict mature;relationship between the entity and the said,is simple and easyto understand;transparent data storage path,independent andsecure better query efficiency is lower than the non relationalmodel.Database application life cycle2.1 software life cycle refers to the entire per
13、iod from whichthe software product starts from its concept and the productis no longer used.Generally includes concept stage,demandphase,design phase,implementation phase,test phase,installation,deployment and delivery phase,operation phaseand maintenance stage.The database application system is the
14、demand for the users of the database application systemexpectations and requirements in function,performance,behavior,design constraints and other aspects:data and dataprocessing,business performance,and other storage securitybackup and recovery.2.2 database application system life cycle model1.wate
15、rfall model principle,project planning,demandanalysis,system design,implementation and deployment,operation,management and maintenance of five parts2.rapid prototyping models and incremental model principlesallow for the gradual and iterative development of DBAS.3.according to the DBAS software comp
16、onents and theirrespective functions,refinement of DBAS analysis and designstage,the introduction of a data organization and storagedesign,data access and processing design,design three designlines,respectively,for DBAS in the design of database,database transaction and application program.4.,the de
17、sign phase is divided into three steps:conceptualdesign,logical design and physical design.Each step coversthree main design 1ines.Requirement analysis and function modeling method3.1 data elements(columns)are the smallest units in dataprocessing.ThreeFigure 2 DFD:data stream(marked with name,arrow)
18、processing,data storage,data source(Heng Yuanzhu)/end point(PRISM)3.3 IDEFO diagram:better understanding of requirements;ICOM(input,control,output,mechanism)code;at least one controland output arrow.A-0;AO(top level diagram);Al;AllComparison of 3.4 DFD and IDEFO:structured analysis idea:fromtop to b
19、ottom,step by step,refinementFigure 1.DFD with the arrow is also called the data flow todescribe the data moving in the direction of data processing,data dependencies between IDEFO map is represented by an arrowdata stream,but does not emphasize the flow or order,emphasison data constraints,arrow ri
20、cher semantics.The 2.DFD model has four elements,and there are only two IDEFOdiagrams:arrows and events3.IDEFO diagrams are more standardized.Its concepts,modelingmethods,drawing rules and so on are explained and stipulatedThe 4.IDEFO model is clearer and easier to understand andcommunicate3.5 advan
21、tages of structured analysis and modeling methods:1)but as early as possible into specific details,from theoverall or macro start to analyze problems,such as the overallstructure of the business system,systems and subsystems.2)graphically graphically model objects that intuitivelyrepresent what func
22、tions the system can accomplish tofacilitate system analysts understanding and describingsystems.3)model objects do not involve too many technical terms,whichmakes it easy for users to understand the model.Database conceptual design and data modeling4.1,the purpose and task of conceptual design:to f
23、ace the realworld,to understand and describe the data requirements in theapplication domain,and to analyze and determine what data thesystem needs to store and process.Process:determine entityset;define connection and connection type;establish businessmodel represented by information model;determine
24、 entity setattribute;optimize information model.4.2 entity sets describe collections of things with the sameattributes,characteristics,and properties;attributesdescribe a particular feature or nature of an entity set4.3,IDEF1X:standard stereotypes(in accordance with theparent instance only calibrati
25、on)(deterministic);non-standard stereotypes(deterministic);classification;uncertaintyRelational database logical design5.1 relational databases:collections of interrelatedrelationships(tables)organized and stored in atwo-dimensional table.Relational databases use relational models to organize,store,
26、process,and manage data in a computer.5.2 master constraint:uniqueness;minimum;cannot take nul1values;and values are uniqueOuter code constraint:if two relations R and S,X is theattribute or attribute group of R,and X is not R code,but Xis S code,then X is R outer code.Or a null value,or equalto the
27、 value of the primary code of a tuple in S.5.3,the content of logical design:define and describe theglobal logical structure of the database,the relation betweendata,the integrality of data,etc.Objective:to get the database schema that can be processed bythe actual database management system.Step by
28、 step:ER diagram transformation relation model;optimization relation model;data integrity design;externalschema designThe static structure of the 5.4 model to describe therelationship between the composed pattern name,attributes,integrity constraints,the relationship is a collection ofrecords in a t
29、able,pay attention to the value of(a set ofpattern instances)is also a reflection of the relationshipmode in a moment.5.5,the integrity of the relationship(integrity constraints):the conditions for the relationship to meet the definition.Role:to define and check the validity and correctness of thein
30、stance contained in the database.Static:main code,extracode,domain(user defined);dynamic:Based on business rules5.6 pseudo transitive rules:X-Y,YW-Z,then XW-Z isestablished.5.7,the main content of the normalized design theory is theparadigm,that is,the condition of the relational schemasatisfying.It
31、 is a guide to the logical design of databasesand a standard to measure the merits of relational schema design.Objective:to eliminate data redundancy and avoid abnormaloperation,the basic process is to decompose the relation.Therelational schema of a lower normal form can be transformed intoa set of
32、 relational patterns of multiple high-level paradigmsthrough the decomposition(projection)method,which is callednormalization.Each attribute of the 5.8 INF:R cannot be subdivided;2NF:INF,and each non primary attribute is completelydependent on the master code.On 1,the elimination of nonprincipal att
33、ributes depends on the partial function of themain code;3NF:INF,and each non principal attribute depends only on themain code.On 2,the dependence of the transfer function of thenon main genus on the main code is eliminated.5.9 ER model transformation relation model:entity set to thesame name;ties in
34、to a relationship,attribute code and linkedto each entity set to the attribute of the relation(1:1,1:n,m:n and N can be taken in);combined with the same relationshipcodes.Storage technology and physical design of database6.1,physical design is based on the specific hardwareenvironment,OS and DBMS co
35、nstraints,based on logical design,design specific data storage structure and access mode.Objective:less space occupation,high access efficiency andlow maintenance cost.The main steps include database logicalmode adjustment,file organization and access design,datadistribution design,security model de
36、sign,systemconfiguration determination and physical model evaluation.6.2 index(Indexing)is a kind of fast file access technology,it will be documented in a certain domain(or attributes)onthe value of the record and the physical address of a directlink,provides a quick access to the file records acco
37、rding tothe domain of the system of record value.An index file is afile organization and access method that supports fast fileaccess using indexing techniques.The index speeds up the query record,but slows the data updatespeed and itself occupies a certain amount of storage space.6.3 file organizati
38、on:how to map the relationship in therelational database to the database file in the operatingsystem and manage the file.File structure:how to map logical records in a DB file to diskblocks in a physical file.File access:according to a certain structure of the DB file,how to check and record the log
39、ic of Tim excision6.4 data dictionary:database description information of allkinds of objects,database management system controlinformation.Including relational schema information,information related to view description,relational storagestructure and access method information,integrity constraints,
40、security related information,database operation statisticsinformation.Effect:DBA used to monitor DBMS and assist management;generalusers can be used to access part of the database structureinformation;the DBS runtime subsystem is frequently used tocomplete the corresponding function of storage and q
41、ueryprocessing.6.5 DBMS,s three integrity control mechanisms:the CHECK clause,assertion,and triggerAssertion statement:Create assertion asserts constraint namecheck.)6.6 stack files:less data and frequent operations;batchloading data(first selected as heap files,and then adjust thefile structure)Seq
42、uential file:query condition defined on lookup code;fasttwo-bit lookupHash file:an equivalent match based on the hash field value,especially the access order is random.Non precision query;nonhash domainB tree and B+tree:large data quantity basic table;focus file:multi table join operation6.7,the ind
43、ex technique uses index file to realize the mappingrelation between the lookup code and the physical address.Anindex file consists of index records,each of the index entriesthat records a particular lookup code value and the physicaladdress of the data file that has the value.When a data recording r
44、equires access to the data file,according to the search code value access index file,find thecorresponding index,and then find out the physical addressdata recorded in the data file from the index entry access datarecords according to this address.6.8 hash technology is a fast file access technology
45、,it usesthe hash function to achieve the direct mapping relationbetween the value of the file record domain and the physicaladdress of the record.When the need for a Si or some file recordlookup code value to access the data file,hash function outputSi as a hash function H input calculated values of
46、 H(SI)isthe physical address of the file record in the data file.6.9 permissions:allows the user for a given database objectcan perform operations(Tim excision,query,new,backup etc.).Function design of database application system7.1 software architecture:software architecture=component,connector,con
47、straint)7.2 software design includes the overall structure of thesystem design,system design,system design and process dataof three aspects(+interface design),from the point of viewof project management,divided into outline design and detaileddesign7.3 application software is divided into database t
48、ransactionsand applications.On the one hand,the latter can coordinatewith database transactions,on the other hand,it can realizefunctions unrelated to database access,such as communicationand human-computer interaction.7.4 transaction:a collection of operations with logicalindependent functions that
49、 implement certain business rules.7.5,the core of the transaction outline design is to identifyand design the transaction logic of the transaction itself,anddesign the data processing flow and structure of thetransaction by using the data oriented programming method.7.6,C/S structure features:data m
50、anagement and dataprocessing are divided into the client and server;the servercan support multiple clients;the client can also accessmultiple servers;client=human-computer interaction+dataprocessingB/S structure features:presentation layer,WEB browser,function layer,WEB application server,data layer