Database TechnologySession II 10:15 - 11:00

Dr S Sudarshan & Dr D B PhatakIIT Bombay

Data Base Technologies

OVERVIEWStorage devicesFiles and Index Structures Legacy Systems and CobolRelational Databases and SQLTransactions and ACID propertiesSystem ArchitecturesSecurity and Audit

Data Base Technologies

Storage DevicesMain memoryvolatile, lost on power failureexpensive and relatively smallHard disknon-volatile, reasonably fast accessrelatively cheap, and largemain storage system for databasesMean time to Failure: ~5 years

Data Base Technologies

RAID SystemsGoal: improve storage reliabilityData stored on multiple disks if one disk fails, data still available on othersEssential for safety of dataHardware RAIDexpensive, very high availabilityfor 24x7 applications (24 hrs X 7 days/wk)Software RAIDcheaper, use if some downtime is allowable

Data Base Technologies

Storing Data on DisksByte: unit of information one characterFile: sequence of bytesFile system:stores multiple files organizes files into directories/folders

Data Base Technologies

File StructureInformation stored within large filesSequential filessorted on a key (e.g., account number)Index needed for efficient accesse.g. find information of account 2345similar to library card catalogs

Data Base Technologies

Traditional File ProcessingCOBOL: Common Business Oriented languageFiles contain sequence of records, e.g. Record per accountComplex program for each taske.g. withdrawal, deposit, average balance, File structures often very complexmotivated by efficiency, but become hard to understand

Data Base Technologies

SEGMENT OF A SAMPLE COBOL PROGRAM Open Input SALARYTABLE-FILE.Perform Varying I from 1 to 11.Move zero to GROUPTOT [I].END-PERFORM.PROCESS-NEXT.Read EMPTAB-FILE At End Go To End-job.- - - - -Add salary to Group tot [K].Go to Process-Next.END-JOB. - - - -

Data Base Technologies

PROGRAMMING PARADIGMS4 GL: What to doSet processing3 GL: How to do (Algorithm)Record by Record Processing2 GL: Algorithm at the lowest levelDetails of Individual Operations

Data Base Technologies

Relational DatabasesMotivation: simplify storage structureseasy to use language for queries/updatesefficiency is job of systemautomatic optimizationLegacy systemsSystems built using COBOL and older data modelsStill in wide use, but declining usage

Data Base Technologies

Relational Databases Provide: Tabular Data model: simple, yet powerfulA Standard Query Language: SQLMature Products with Reliable, Fault-Tolerant Operations availableGood Performance High number of transactions per secondParallel operation for scalability (handle growth)Distributed and Replicated Data BasesInteroperation, High availability

Data Base Technologies

Relational Model: Tabular DataAccountTransactions

Data Base Technologies

Account Number

Name

Address

Balance

23456

D. B.Phatak

A-12, IIT, Powai

40,000,000

23457

Bill Gates

Microsoft Corp

9999,999,999

23458

S.Sudarshan

C-148, IIT Powai

1,000

Date

Acct Num

Debit

Credit

Balance

1/4/99

23458

2000

3000

1/4/99

23456

2000

3000

4/4/99

23456

9000

12000

4/5/99

23456

200000

212000

4/5/99

23458

4000

7000

Querying the Database using SQLselect name, balance from account where name = D. B. Phatak insert into transactions values (3/5/99, cash, 5000, -, 14000)select acct-num, avg(balance) from transactions where date between 1/4/99 and 30/4/99 groupby acct-num

Data Base Technologies

Transactions: ACID PropertiesTransactions: e.g. Debit/credit Problems:Failures (e.g., power, disk storage)Concurrent transactionsSolution:Support for ACID properties

Data Base Technologies

ACID PropertiesAtomicity: Transaction appears to either run completely or not at all -- no partial stateConsistency: Integrity checks (e.g., balance >= 0)Isolation: Locks on data so that transactions do not step on each others toesDurability: Data/updates are never lost

Data Base Technologies

Database Application ClassesOLTP: Online Transaction Processingsupports many small transactionsDecision SupportSummaries/aggregatesOLAP: Online Analytical Processing

Data Base Technologies

Performance IssuesImportant for high volume systemse.g., internet bankingSizing / Performance tuningdeciding on CPUs, memory size, disk size, number of disks, etctuning transaction code to reduce disk I/Oto reduce lock conflicts between concurrent transactionsScalability via parallelismSmoothly handling more traffic as the business grows

Data Base Technologies

Access SecurityAuthenticationIdentifying who a person isPasswordswidely used, but quite insecureSmart cards, biometrics, etcMore on this laterAccess privilegeswho is allowed to do whatAudit trailTrace back what happened

Data Base Technologies

Authorization MechanismsPrivilegese.g., read table, update table, insert row in table, delete row from table, privilege to grant privilegesEach user given specific set of privileges he/she needs Rolesprivileges given to roles (e.g., teller, manager) users authorized to play roles

Data Base Technologies

Audit TrailsDatabase keeps track of all transactions in an audit tablewhat the transaction did, and who ran itMechanisms for tracing back what transactions affected a particular entity (such as an account)

Data Base Technologies

MORE ON SECURITYEncryption, Session KeyData Encryption Standard (DES-3)Shared Private keyRSA, DH AlgorithmsPublic/Private key

Data Base Technologies

SQLSQL is Intergalactic DataspeakStrong Data Definition Language (DDL)Domain DefinitionsIntegrity ConstraintsSecurity & Access Control ProvidedViews, PermissionsInteractive Queries

Data Base Technologies

SQLEmbedded SQL:Use of SQL commands from within 3GL programs (programs in C/COBOL/)Open Data Base Connectivity (ODBC): Standard for client server interconnectivity, using C languageJDBC: Like ODBC, for Java languageSQL Standards: 86, 89, 92, SQL-3 Draft

Data Base Technologies

SQLNo Standards for User Interface Screens (Forms & Menus)ReportsSpecial Tools AvailableNative to ProductIndependent Vendors 24

Data Base Technologies

DATABASE SERVERSMajor playersOracle, IBM DB2, Microsoft SQL Server, Informix, Sybase, IngressWide range of performance, features, and price

Data Base Technologies

Database ArchitecturesCentralizedDumb terminals connected to single serverClient ServerSmarter client machines connect to serverMain work still done at serverParallel ServersWork divided between multiple CPUsDistributedMultiple independent databases in cooperation

Data Base Technologies

EVOLUTION OF CLIENT SERVER COMPUTINGMultiple Computers to Independently Handle Component Tasks of an ApplicationNeed to Partition Tasks Judiciously

Data Base Technologies

TWO TIER PARTITIONING

Data Base Technologies

Distributed Remote Distributed Remote Data Distributed Data

Presentation Presentation Application Logic Management Management

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CLIENT - SERVER TERMINOLOGYService: Provided by the ServerEach Client Is a ConsumerShared Resources : Managed by ServerClient : Initiator of a Request

Data Base Technologies

SERVERSFile Servers : NovellDatabase Servers : SQLTransaction Servers : OLTPTP lite (Stored Procedures)TP heavy (TP monitors)

Data Base Technologies

SERVER FUNCTIONSWait for RequestsHandle Concurrent TransactionsTake care of VIP requestsAssign prioritiesAuthentication, Authorisation Audit trails

Data Base Technologies

CLIENT FUNCTIONSTypically Processes Running on Front-end Machine (PC)Provide User InterfaceSupport Graphics, Multimedia

Data Base Technologies

THREE TIER C/STier One : ClientTier Two : Application ServerTier Three: Database Server

Data Base Technologies

MORE C/S TERMINOLOGYThin or Fat Client Fat Servern-Tier ArchitectureOOUI

Data Base Technologies

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