database review 1a

8/13/2019 Database Review 1a

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2. Data Models for Database Systems2 - 1

Data World

- Databaserepresents a real world which is changingcontinuously

-Data model is the procedure for representing a real world

3 Data Worlds

real world(reality) conceptual world(concept) computer world(data)

infornation

modeling

data

modelingobject

propertiesvalues

entity set

attributes

values

record type

field

values


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Data World (cont'd)

Database and Real World

real world conceptual worldinformation

modeling

data

modeling

logical data structure

storeddatabase

data

structuringconsistency

database

design


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Data Model Concepts

Data model- conceptual tools for describing data and data relationship

- specify the overall logical structure of database

Data models fall into three different group : conceptual data model,

logical data model and physical data model.

Conceptual data model (High-level)

- relationship between entity sets, not considering physical storage

device

- human oriented data model

- facilitate database design

- Entity-Relationship (E-R) model

- OO data model


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Data Model Concepts (cont'd)

Logical data model (Representational, Implementation)

- describing relationship between data field (record-based)

- overall logical structure of a database

- high level description of the implementation

- hierachical model

collection of trees

- network model

collection of record types and links, i.e.,graphs- relational model

collection of tables


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Data Model Concepts (cont'd)

Physical data model (Low-level)

- describe how data is stored in the computer

- e.g. record format, record orderings, and access paths

data

modeling

logical, representational model

(logical data structure)

storeddatabase

data

structuringconsistency

physical, low-level model


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E-R Model

- by Peter Chen, 1976

- based on a perception of real world which consists of a set of basic

objects called entitiesand relationshipsamong these objects

-E-R diagram is graphical database structure in E-R model which

is consist of entity set, relationship, attributeand link

Entity- an object that exists and is distinguishable from other objects

- ex) Yoon S. A. with social security number 700123-1684321

- may be abstract, such as a holiday or a concept


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E-R Model (cont'd)

EntitySet

- a set of entites of the same type

- ex) customer: set of all persons having an account at a bank

account: set of all accounts maintained at a bank

- rectangles, which represent entity sets- entity sets need notbe disjoint

a person entity may be an (bank) employee entity,

a customer entity, both, or neither

Attribute

- entity is represented by a set of attributes

- ex) customer entity set's attributes arecustomer-name,

security-number, street, and customer-city



E-R Model (cont'd)

Domain

- a set of permitted values

- ex) domain of customer--name: set of all text strings

of a certain length

Relationship- an association among several entities

- ex) Harris(customer) 401(account)

Relationship Set

- a set of relationships of the same type- {(e1, e2, ... , en) | e1 E1, e2 E2, ... , en En}

- ex) CustAcctdenote association between customersand accounts

- ternary relationship set CAB : Harris, 401, and Redwood



E-R Model (cont'd)

Attribute of Relationship

- relationship set can have attributes

- ex) CustAcct's (Harris, 401) has property {(date, 20 Sept 1995)}



Example



Constraints on Relationship Set

Cardinality ratio constraint

number of entities to which another entity can be associated

- one-to-one : for each entity in either set, there is at mostone associated member of the other set

Emp Depte1e2

e3

e4

.

.

d1

d2

d3

d4

d5

.

..

.

Manages



Constarints on Relationship Set (cont'd)

- many-to-one : each entity in E1(Courses) is associated with at

most one entity in E2(Teachers), but each entity

in E2 can be associated any number of entities in E1

Courses Teacherstaught-by

- many-to-many : no restriction

Countries Productsexport




Participation constraintthe existence of an entity depends on the existence of

the relationship to another entity

- existency dependencythis means that ifyis deleted, so isx

dominant entity,

strong or regular entity

subordinate entity,

weak entity




Account Log Transaction

account# Balance transaction# date amount

462-21-23 3,000 1 11 Oct 1996 +50

262-45-20 6,000 4 12 Oct 1996 +350

645-44-09 5,000 7 12 Oct 1996 - 150

... ...

dominant, strong subordinate, weak


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Keys

it is important to be able to discriminate how entities and

relationships

Superkey

- a set of one or more attribute wich allow us to identifyuniquely an entity in the entity set

- may have unnecessary attributes to distinct

Candidate Key

- minimal superkey

Primary Key

- a candidate key chosen by the DB designer


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E-R Diagram

graphical database structure in E-R model

- rectangle : (strong) entity set

- double rectangle : weak entity set

- ellipse : attribute

- diamond : relationship set- line : (1) link attribute to entity set

(2) link entity set to relationship set

see Slide 2-11


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Reducing E-R diagrams to Tables

(1) Representation of strong entity sets

D1X D2X ..... Dnsee Fig. 2-14, Fig. 2-15 Korth Book

(2) Representation of weak entity sets

{attributes of weak entity set} U {primary key of strong entity set)see Fig. 2-16

(3) Representation of relationship sets

{primary key set} U {attribute of relationship set R)

see Fig. 2-17, Fig 2-18


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Account Log Transaction

account# Balance date transaction# date amount

Reducing E-R diagrams to Tables (Ex)

(1)

(2)

(3)


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Generalization

There are similarities between the checking-accountentity set and

thesaving-account entity set in the sense that they have several

attribute in common. This commonalitycan be expressed by

generalization.

- Creation method : create a high-level entity set from two or more

lower level entity set's common attributes

- Usage : is used to emphasize thesimilaritiesamong lower level

entity type and to hide their differences

- Inheritance: lower level entity set (saving-accountand checking

account) inherit the attributes of higher level entity set (account)


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account

number

Generalization (cont'd)

balance

account

saving-

account

ISA

checking-

account

interest-

reteoverdraft-

amount

saving-account is an

account

account

number

balance

account

number

balance


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Generalization (cont'd)

Transforming E-R diagram including generalization totabular form

(1) Primary key of high-level entity set plus lower level entity sets

account + savings-account, checking-account

(2) Only lower level entity sets

savings-account, checking-account (including higher-level

attributes)


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Aggregation

One limitationof the E-R model is that is not possible to express

relationship among relationships

- Aggregation is anabstraction through which relationships are

treated as high-level entities

hospital

hospitalization

treatment patientsdoctor1 n

m

1


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DATA MODEL TYPES


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Hierarchical Data Model

Basic Concepts and Structure- Hierarchical database consists of a collection of recordswhich

are connected to one another records through links

- record : collection of fields (attributes)

link : inary relstionship (parent-child relationship)* restriction : only one-to-many

subject

studentlecturer

lectureprerequisitesubject

Hierarchical Definition Tree

(subjectdatabase schema)


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Hierarchical Data Model (cont'd)

subject

student

lecturer

lecture (record type)prerequisite

subject

subject Database Tree

(record occurrence)

C100 Database 3

L1 Tue-Thu 2-204L2 Mon-Wed 3-403

S93001 Park E. Y. 90S93002 Hur S. 92

S93002 Lee S. H. 85

P94 Kim C. S. Computer

C99

ordered tree

one-to-many


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Characteristics

- parent-child relationship is one-to-many relationship

- ordered tree (left to right)

- n:m relationship can be represented by two 1:n representations

Restrictions

- all record occurrences except root record, must be connected

to parent record

* need to connect its parent for record insertion

* have to delete all its child record for record deletion- one-to-many relationship : to associate with two its parent,

make another tree (m:n => two 1:n relationship)

Hierarchical Data Model (cont'd)


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Network Data Model

Basic Concepts and Structure- Network database consists of a collection of recordswhich

are connected to one another records through links

but, Data Structure Diagram (DSD) which represent logical

structure of network database, is networkform- extension of hierarchical data model

- CODASYL(Conference on Data Systems Language) DBTG

(Data Base Task Group) proposed the network data model formally

many-to many link is not allowed (implementation problem)

- Network Database System :IDMS (Computer Associates)

TOTAL (Cincom Systems)

IDS II (Honeywell Information Systems)


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Network Data Model (cont'd)

Data Structure Diagram (DSD)

customer

name street city

branch

name assets city

number balance

account

CustAcct BrncAcct


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Network Data Model (cont'd)

Set Occurrence (database value)

Kim Daesin Pusan

Chung Choongmu Seoul

Lee Hanbat Taejon

Uam 5,000,000 Pusan

Namsan 2,000,000 Ulsan

305 500

226 336

177 205

155 62

402 100

408 300

1: nrelationship

graph


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Relational Data Model

Background- Proposed by E. F. Codd (1970, ACM TODS)

- Non-procedual database language (easy to use)

- Standard database language : SQL

* ISO, ANSI, X/Open* SQL, SQL89, SQL2, SQL3, ....

- Theoretical background (mathematics-based)

- Relational DBMSs :

Oracle - 2nd largest S/W maker in the world

Informix - UNIX RDBMS special group

Sybase - Client/Server DBMS

Ingres - ?


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Relational Data Model (cont'd)

OverviewRelational model = structure + constraints + operation

Structure

- Domain : set of atomic values

- Relational scheme : set of attribute names- Relation : any subset of the Cartesian product of domains

of attributes int relation scheme

Set of Tuples

Employee E# Ename City

10 Smith LA

20 James NY

Workfor Ename Dname

Smith Physics

James Mathematics


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- Terminologies

table : relation

row : tuple

column : attribute

- Arity(degree)number of attribute in the relation

- Tuple

ordered list of values from domain D1, D2, ... , Dn

mapping from attribute names to values in the domainsex) (10, Smith, LA)

m(E#) = 10, m(Ename) = Smith, m(City) = LA


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Integrity Constraints

- Entity integrity constraint

no primary key can be null

- Referential integrity constraints (foreign key constraints)

foreign key : set of attributes which is the primary keyof another relation

(ex) Dept = (Dname, Manager, Budget)

Employee = (Ename, Bdate, Salary,Dname)

Every value of the foreign key must existin the set of thecorresponding primary key values of another relation(Dept)

foregin key


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Operation

- Operation to manipulate a relation is needed

- There are two types of operation, Relational Algebra and

Relational Calculus

Relational Algebra (How)

query is expressed by applying specialized algebraic

operators operators => SQL

Relational Calculus (What)

query is describes a desired set of tuples by specifying apredicate the tuples must satisfy => QUEL, QBE



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Object-Oriented Data Model

Shortcomings of the Conventional Database Technology

- Too simple for modeling complexnested entities

- A limited set of atomic data types

- No frequently usefulsemanticconcepts

-Impedance mismatchbetween programming languageand database language

- Inappropriate for long-duration transactions necessary in

interactive, cooperative design environments (CAD)

- Unacceptable for various types of computer-intensiveapplications


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Object-Oriented Data Model (cont'd)

Additional Features of the Next-Generation Database

Systems

- Represent and manipulate complex nested objects

- Store and retrieve arbitary long data- Define and manipulate arbitary data types

- Represent and manipulate varioussemantic modeling concepts

- Specify rulesand extented constraints to support inferencing

and constraint management

- Manage long-duration cooperative transactions


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Object-Oriented Approach

- in Programming language

from SIMULA-67 (K. Nygard, Norway)

Smalltalk, Eiffel, C++, Java

- in Artificial Intelligencefrom introduction of FRAME

KEE, ART

- in Database

from semantic data modelE-R, EE-R, SDM, DAPLEX


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Core Modeling Concepts

- Object and Object Identifier

object = data + operation

- Attribute and Methodsattribute : specified property to represent an object

method : an operation of an object ( = code)

- Encapsulation and Message passing

encapsulation : the data of an object can only be accessed viathe methods of the objects

message : a request to perform an operation

Balance

5000

Accountobject

deposit

withdraw

A#

100


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- Classclass : a templatefrom which objects with the same

representation and the same behavior can be created

- Class Hierarchy and Inheritance

inheritance : a mechanism which allows a new class to beincrementally defined from an existing class


object 1object 2

class

instantiation instantiation


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Object-Oriented Database Concepts

Name Age Salary

Lee 25 500,000data part

operation part (hire, change Age, change Salary)

EMPLee is an EMP object

Balance

5000

Accountobject

pay-interest A#

100

: all 6%

: $1000 -> 5%$1000 -> 6%

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