week 3 september 12

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R. Ching, Ph.D. • MIS Dept. • California State University, Sacramento

Week 3Week 3September 12September 12

• Three-Level ArchitectureThree-Level Architecture• Database Management System (DBMS)Database Management System (DBMS)

• Relational Data ModelRelational Data Model• ViewsViews

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Privacy and ConfidentialityPrivacy and Confidentiality

SSN: 123 45 6789Customer: John K SmithAddress: 1234 Main Street

Dallas, TX 68213

Account: 5432 1234 4567 8901 Credit limit: 20,000Current balance: 9,123.00Employer: Enron Corp.Monthly income: 100,000.00

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Schema and SubschemasSchema and Subschemas

SchemaSchemaSchemaSchema

DBMS SoftwareDBMS SoftwareDBMS SoftwareDBMS Software

Individual Individual ViewsViews

Complete catalog of all data Complete catalog of all data retained in the databaseretained in the database

Manages the databaseManages the database

Physical DatabasePhysical Database

SubschemaSubschemaSubschemaSubschema SubschemaSubschemaSubschemaSubschema SubschemaSubschemaSubschemaSubschema

UserUserUserUser UserUserUserUser UserUserUserUser UserUserUserUser UserUserUserUser UserUserUserUser

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Database EnvironmentDatabase EnvironmentThree Level ArchitectureThree Level Architecture

External External LevelLevel

Conceptual LevelConceptual Level

Internal LevelInternal Level Internal SchemaInternal SchemaInternal SchemaInternal Schema

Physical data Physical data organizationorganization

User’s view of the databaseUser’s view of the database

Community Community viewview

Physical Physical representationrepresentation

Physical storagePhysical storage

Conceptual SchemaConceptual SchemaConceptual SchemaConceptual Schema

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IndependenceIndependence

• Each user should be able to access the same data, but have Each user should be able to access the same data, but have a different customized view of the dataa different customized view of the data

• Users should not have to deal directly with physical Users should not have to deal directly with physical database storage detailsdatabase storage details

• The DBA should be able to change the database storage The DBA should be able to change the database storage structures without affecting the users’ viewsstructures without affecting the users’ views

• The internal structure of the database should be unaffected The internal structure of the database should be unaffected by changes to the physical aspects of storageby changes to the physical aspects of storage

• The DBA should be able to change the conceptual or The DBA should be able to change the conceptual or global structure of the database without affecting all usersglobal structure of the database without affecting all users

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Three-Level ArchitectureThree-Level Architecture

• External LevelExternal LevelDescribes that part of the database that is relevant to a Describes that part of the database that is relevant to a particular userparticular user

• Conceptual LevelConceptual LevelDescribes Describes whatwhat data is stored in the database and data is stored in the database and relationships among the datarelationships among the data

• Internal LevelInternal LevelDescribes Describes howhow the data is stored in the database the data is stored in the database

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Conceptual SchemaConceptual Schema

Internal SchemaInternal SchemaConceptual/internal Conceptual/internal

mappingmapping

SubschemaSubschema SubschemaSubschema SubschemaSubschema

Ext

erna

lE

xter

nal

Con

cept

ual

Con

cept

ual

Inte

rnal

Inte

rnal

Logical data Logical data independenceindependence

Physical data Physical data independenceindependence

External/conceptual External/conceptual mappingmapping

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Internal SchemaInternal SchemaConceptual/Conceptual/

internal mappinginternal mapping

Ext

erna

lE

xter

nal

Con

cept

ual

Con

cept

ual

Inte

rnal

Inte

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Internal SchemaInternal SchemaConceptual/internal Conceptual/internal

mappingmapping

Ext

erna

lE

xter

nal

Con

cept

ual

Con

cept

ual

Inte

rnal

Inte

rnal





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Data IndependenceData Independence

• Logical data independenceLogical data independenceImmunity of external schemas to changes in the conceptual Immunity of external schemas to changes in the conceptual schemaschema

• Physical data independencePhysical data independenceImmunity of the conceptual schema to changes in the Immunity of the conceptual schema to changes in the internal schemainternal schema

““Plug and Play!”Plug and Play!”

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Database EnvironmentDatabase Environment



Individual Individual ViewsViews

Complete catalog of all data Complete catalog of all data retained in the databaseretained in the database


Physical DatabasePhysical Database



Shared and ManagedShared and Managed

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File-Based SystemsFile-Based Systems





FileFileFileFile FileFileFileFile

Each user has Each user has his/her filehis/her file

FileFileFileFileEveryone has access Everyone has access to all data in the fileto all data in the file

FileFileFileFileIntegrity ProblemsIntegrity ProblemsIntegrity ProblemsIntegrity Problems

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Database Languages: DDL vs. DMLDatabase Languages: DDL vs. DML

• Data definition language (DDL)Data definition language (DDL)Used to describe name the entities required for the Used to describe name the entities required for the application and the relationships that may exist between application and the relationships that may exist between the different entitiesthe different entities

– Specify or modify the database schema and subschemasSpecify or modify the database schema and subschemas

• Data manipulation language (DML)Data manipulation language (DML)Provides a set of operations that support the basic data Provides a set of operations that support the basic data manipulation operations the datamanipulation operations the data

– Read and update (i.e., insert, update, delete) the Read and update (i.e., insert, update, delete) the databasedatabase

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ModelsModels

• Represents the real thingRepresents the real thing

• Identifies the components and their interactionsIdentifies the components and their interactions

• Specifies the behaviorSpecifies the behavior

For example...For example...

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Data ModelsData Models

• An integrated collection of concepts for describing and An integrated collection of concepts for describing and manipulating data, relationships between data and manipulating data, relationships between data and constraints on the data in an organizationconstraints on the data in an organization

• Three components:Three components:

– Structural part - set of rules applied to the construction Structural part - set of rules applied to the construction of the databaseof the database

– Manipulative part - defines the types of operations Manipulative part - defines the types of operations allowed on the dataallowed on the data

– Integrity rules - ensures the accuracy of the dataIntegrity rules - ensures the accuracy of the data

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Data ModelsData Models

• Object-basedObject-based– Entity-relationshipEntity-relationship– SemanticSemantic– FunctionalFunctional– Object-orientedObject-oriented

• Record-based (transactions)Record-based (transactions)– RelationalRelational– NetworkNetwork– HierarchicalHierarchical

• PhysicalPhysical– UnifyingUnifying– Frame memoryFrame memory

How data are storedHow data are stored

Transaction-basedTransaction-based

Knowledge-basedKnowledge-based

Object-relationalObject-relational

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Record-Based Data ModelsRecord-Based Data Models

• Relational (Oracle, DB2, Sybase, Informix, SQL 7, Ingres, Relational (Oracle, DB2, Sybase, Informix, SQL 7, Ingres, etc.)etc.)– Based on concepts of mathematical relationsBased on concepts of mathematical relations– Tables, rows, columnsTables, rows, columns

• Network (CODASYL - COnference on DAta SYstem Network (CODASYL - COnference on DAta SYstem Languages) (Image)Languages) (Image)– Many-to-many Many-to-many relationshipsrelationships– Record types, data itemsRecord types, data items

• Hierarchical (IMS)Hierarchical (IMS)– Segment types, fieldsSegment types, fields

In COBOL: files, records, fieldsIn COBOL: files, records, fields

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DatabaseDatabase

DBMSDBMS

Management Management QueriesQueries

Application Application ProgramsPrograms

Other Other SoftwareSoftware

Physical Physical DatabaseDatabase


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Functions of a DBMSFunctions of a DBMS

• Data storage, retrieval and updateData storage, retrieval and update

• User-accessible catalogUser-accessible catalog

• Transaction support Transaction support

• Concurrency control services Concurrency control services

• Recovery servicesRecovery services

• Authorization servicesAuthorization services

• Support for data communicationsSupport for data communications

• Integrity servicesIntegrity services

• Services to promote data independenceServices to promote data independence

• Utility servicesUtility services

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DBMSDBMS

Program Object Program Object CodeCode

Database Database ManagerManager

Dictionary Dictionary ManagerManager

ProgrammersProgrammers UsersUsers DBADBA

DML ProcessorDML Processor Query ProcessorQuery Processor DDL ProcessorDDL Processor

ApplicationApplicationProgramsPrograms

ApplicationApplicationProgramsPrograms QueriesQueriesQueriesQueries DatabaseDatabase

SchemaSchemaDatabaseDatabaseSchemaSchema

Access MethodsAccess Methods File ManagerFile Manager

System BuffersSystem Buffers

DBMSDBMS

Operating Operating SystemSystem

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Database ManagerDatabase Manager

Authorization Authorization ControlControl


Integrity CheckerIntegrity Checker Command Command ProcessorProcessor

Query Query OptimizerOptimizer

Transaction Transaction ManagerManager SchedulerScheduler

Buffer ManagerBuffer ManagerRecovery Recovery ManagerManager

Data ManagerData Manager

Checks user authorizationChecks user authorization

Checks integrity Checks integrity constraintsconstraints

Processes queryProcesses queryDetermines optimal strategyDetermines optimal strategy

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Transfers data between Transfers data between primary and secondary primary and secondary storagestorage

Performs command Performs command operationoperation

Ensures recovery in case of failuresEnsures recovery in case of failures

Manages concurrent operationsManages concurrent operations

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Transfers data between Transfers data between primary and secondary primary and secondary storagestorage

Performs command Performs command operationoperation

Ensures recovery in case of failuresEnsures recovery in case of failures

Manages concurrent operationsManages concurrent operations

Query Query Transaction Transaction Journal Journal Buffered Buffered OS OSQuery Query Transaction Transaction Journal Journal Buffered Buffered OS OS

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System CatalogSystem Catalog

• A repository of information describing the data in the A repository of information describing the data in the database (metadata)database (metadata)

• StoresStores– Names of users authorized to access the DBMSNames of users authorized to access the DBMS– Names of all data items in the databaseNames of all data items in the database

• Types and sizesTypes and sizes• ConstraintsConstraints

– Data items and authorization level granted to each userData items and authorization level granted to each user• Active vs. PassiveActive vs. Passive• Integrated vs. StandaloneIntegrated vs. Standalone

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Relational Data ModelRelational Data Model

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CriteriaCriteria

Relational ModelRelational Model

• ObjectivesObjectives

– A degree of data independenceA degree of data independence

– Address data semantic, consistency and redundancy Address data semantic, consistency and redundancy problemsproblems

– Set-oriented data manipulation languageSet-oriented data manipulation language

• Structured Query Language (SQL)Structured Query Language (SQL)

Data SetData Set

Presen-Presen-tation tation methodmethod

DatabaseDatabase

InformationInformation

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Data SetData Set



Data SetData Set


Data SetData Set


DatabaseDatabase

CriteriaCriteria

Crit

eria

Crit

eria

Criteria

Criteria



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Tuples Tuples (rows)(rows)• CardinalitiyCardinalitiy = =

number of number of tuplestuples

RelationRelation

AttributesAttributes (columns) (columns)• Degree of a relation = number of attributesDegree of a relation = number of attributes

Attrib

ute-

1

Attrib

ute-

1Attr

ibut

e-2

Attrib

ute-

2

Attrib

ute-

n

Attrib

ute-

n

EntityEntity

Domain = all values an attribute can assumeDomain = all values an attribute can assume

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Domain of an AttributeDomain of an Attribute

• Set of allowable values for one or more attributesSet of allowable values for one or more attributes

DomainDomain DomainDomainUnionUnion

ororIntersectionIntersection


Attribute 1Attribute 1 Attribute 2Attribute 2

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Properties of RelationsProperties of Relations

• Distinct (i.e., unique) relation nameDistinct (i.e., unique) relation name

• Each cell contains exactly one atomic (single) value Each cell contains exactly one atomic (single) value

– No repeating groupsNo repeating groups

• Distinct attribute nameDistinct attribute name

• The values of an attribute come from the same domainThe values of an attribute come from the same domain

• Order of attributes has no significanceOrder of attributes has no significance

• Each tuple is distinct (i.e., unique)Each tuple is distinct (i.e., unique)

– No duplicate tuplesNo duplicate tuples

• Order of tuples has no significanceOrder of tuples has no significance

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Unique Identification of a RelationUnique Identification of a Relation

RelationRelation

keykey

SuperkeySuperkey

Candidate keyCandidate key

Primary keyPrimary key

Foreign keyForeign key??

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Identifying a TupleIdentifying a Tuple

• SuperkeySuperkeyAn attribute or a set of attributes that uniquely identifies a tuple An attribute or a set of attributes that uniquely identifies a tuple within a relationwithin a relation

• Candidate keyCandidate keyA super key such that no proper subset is a superkey within the A super key such that no proper subset is a superkey within the relationrelation– Uniquely identifies the tuple (uniqueness)Uniquely identifies the tuple (uniqueness)– Contains no unique subset (irreducibility)Contains no unique subset (irreducibility)

• Primary keyPrimary keyThe candidate key that is selected to identify tuples uniquely The candidate key that is selected to identify tuples uniquely within a relationwithin a relation– Should remain constant over the life of the tupleShould remain constant over the life of the tuple– Most Most efficient efficient way of identifying a tupleway of identifying a tuple

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Finding the Primary KeyFinding the Primary Key

Super KeySuper Key

Candidate KeyCandidate Key

Primary keyPrimary key

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KeysKeys

AttributesAttributes• Catalog numberCatalog number• Record titleRecord title• Artist nameArtist name• Record labelRecord label• UPCUPC

CDs RelationCDs Relation

129341129341

129342129342

129343129343

129344129344

Help!Help!

Hard Day’s NightHard Day’s Night

Sergeant Pepper’sSergeant Pepper’s

Magical Mystery TourMagical Mystery Tour

BeatlesBeatles

BeatlesBeatles

BeatlesBeatles

BeatlesBeatles

ColumbiaColumbia

ColumbiaColumbia

ColumbiaColumbia

ColumbiaColumbia

129345129345 Abbey RoadAbbey Road BeatlesBeatles AppleApple

1-29150-8384-01-29150-8384-0

1-29150-7115-01-29150-7115-0

1-29150-2484-01-29150-2484-0

1-29150-7515-01-29150-7515-0

1-15700-9510-01-15700-9510-0

Superkey?Superkey?Candidate key?Candidate key?Primary key?Primary key?

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Selecting a KeySelecting a Key

• CriteriaCriteria

– An An efficientefficient way of identifying an entity way of identifying an entity

– The attribute (value) remains constant over the life of The attribute (value) remains constant over the life of the entitythe entity

• Never changesNever changes

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Identifying a TupleIdentifying a Tuple

• Foreign keyForeign keyAn attribute or set of attributes within one relation that An attribute or set of attributes within one relation that matches the candidate key of some (possibly the same) matches the candidate key of some (possibly the same) relationrelation

RelationRelation

keykey

keykey

RelationRelation

foreign keyforeign key

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Foreign KeyForeign Key

CDs RelationCDs Relation

129341129341

129342129342

129343129343

129344129344

Help!Help!

Hard Day’s NightHard Day’s Night

Sergeant Pepper’sSergeant Pepper’s

Magical Mystery TourMagical Mystery Tour

BeatlesBeatles

BeatlesBeatles

BeatlesBeatles

BeatlesBeatles

COLCOL

COLCOL

COLCOL

COLCOL

129345129345 Abbey RoadAbbey Road BeatlesBeatles APPAPP

1-29150-8384-01-29150-8384-0

1-29150-7115-01-29150-7115-0

1-29150-2484-01-29150-2484-0

1-29150-7515-01-29150-7515-0

1-15700-9510-01-15700-9510-0

COLCOL

APPAPP

Columbia RecordsColumbia Records

Apple RecordsApple RecordsRecording Label Recording Label

RelationRelation(home relation)(home relation)

Must match!Must match!

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Relational IntegrityRelational Integrity

Constraints placed on the set of values allowed for the Constraints placed on the set of values allowed for the attributes of a relation.attributes of a relation.• Entity integrityEntity integrity

– No attribute of a primary key can be null (every tuple No attribute of a primary key can be null (every tuple must be uniquely identified)must be uniquely identified)

• Referential integrityReferential integrity– If a foreign key exists in a relation, either the foreign If a foreign key exists in a relation, either the foreign

key value must match a candidate key value of some key value must match a candidate key value of some tuple in its home relation, or the foreign key value must tuple in its home relation, or the foreign key value must be wholly null (i.e., no key exists in the home relation)be wholly null (i.e., no key exists in the home relation)

• Enterprise constraints (organizational)Enterprise constraints (organizational)

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Null ValueNull Value

• Absence of any value (i.e., unknown or nonapplicable to a Absence of any value (i.e., unknown or nonapplicable to a tuple)tuple)

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ViewsViews

• A view is a A view is a virtual relation virtual relation or one that does not actually or one that does not actually exist, but exist, but dynamically deriveddynamically derived– Can be constructed by performing operations (i.e., select, Can be constructed by performing operations (i.e., select,

project, join, etc.) on values of existing base relations project, join, etc.) on values of existing base relations • Base relation - a named relation, corresponding to an Base relation - a named relation, corresponding to an

entity in the conceptual schema, whose tuples are entity in the conceptual schema, whose tuples are physically stored in the databasephysically stored in the database

• View - a dynamic result of one or more relational View - a dynamic result of one or more relational operations operating on the base relations to produce operations operating on the base relations to produce anotheranother

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Schema and SubschemasSchema and Subschemas

DBMS

Schema Conceptual LevelConceptual Level

External External LevelLevel

Internal LevelInternal LevelPhysical DatabasePhysical Database

DBMS SoftwareDBMS Software

User User User User User User

Subschema

SomeSome end-user applications end-user applications can be supported by can be supported by viewsviews

Subschema Subschema

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ViewsViews

KeyKeyForeign Foreign

KeyKey KeyKey

CriterionCriterion

Base Relation RBase Relation R Base Relation SBase Relation S

ViewView

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Purpose of ViewsPurpose of Views

• Provides a powerful and flexible security mechanism by Provides a powerful and flexible security mechanism by hiding parts of the database from certain usershiding parts of the database from certain users

• Permits user access in a way that is customized to their Permits user access in a way that is customized to their needsneeds

• Simplify complex operations on the base relationsSimplify complex operations on the base relations

• Designed to support the external model Designed to support the external model

• Provides logical independenceProvides logical independence

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Updating ViewsUpdating Views

• Allowed on views Allowed on views

– Derived from a single base relation, andDerived from a single base relation, and

– Containing the primary key or a candidate keyContaining the primary key or a candidate key

• NOT allowed on viewsNOT allowed on views

– Derived from multiple base relationsDerived from multiple base relations

– Involving aggregations (i.e., summations) or groups Involving aggregations (i.e., summations) or groups operationsoperations

• Vendors may have other constraints on updating viewsVendors may have other constraints on updating views

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week 3 september 12

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