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IST 210

1

Databases and DBMSs

Todd S. BacastowJanuary 2005

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IST 210 Evolution

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IST 210 Ways of storing data

Files (1960) (ancient times)

Databases

Hierarchical (1970)

Network (1970)

Relational (1980)

Object (1990)

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IST 210 File terms

Record

data items related to a single logical entity (e.g.a students information) or row in a table

Field a place for a data item in a record (first name

field in a student record) or a column in a table

File

a sequence of records of the same type (thetable)

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IST 210 File structures

3 Smith Jane A

1 Wood Bob C

2 Kent Chuck B

4 Boone Dan B

ID Last First Grade

record

fieldA file: STUDENT

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IST 210 File organization

Serial

new records appended

Sequential

records ordered in file, usually according toa numeric key

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Serial

list of entries in

which the orderof entry into thelist determinesthe order of thelist

3 Smith Jane A

1 Wood Bob C

2 Kent Chuck B

4 Boone Dan B

ID Last First Grade

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Search of a simple

list entails goingthrough each recorduntil the query issatisfied (linear

search), which isinefficient

3 Smith Jane A

1 Wood Bob C

2 Kent Chuck B

4 Boone Dan B

ID Last First Grade

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Sequential

list of entriesordered in someway (e.g.numerically oralphabetically)

1 Wood Bob C

2 Kent Chuck B

3 Smith Jane A

4 Boone Dan B

ID Last First Grade

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Search of an

orderedsequential list canuse a searchmethod

1 Wood Bob C

2 Kent Chuck B

3 Smith Jane A

4 Boone Dan B

ID Last First Grade

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Indexes provide a reference to records based on an indexfield, which is ordered

Boone *

Kent *

Smith *

Wood *

1 Wood Bob C

2 Kent Chuck B

3 Smith Jane A

4 Boone Dan B

ID Last First GradeLast Pointer

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IST 210 Problems with files

Redundancy number of files grows with

applications, and data isduplicated

Inconsistency data is updated in one

applications files, but not inanothers

Maintenance problems changes to data structures

mean changes to manyprograms

Difficulty combining data business needs may mean

users want data fromdifferent applications

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IST 210 Other ways to organize

Data model

A data model is a particular way of conceptually organizingmultiple data files in a database

Other common models

Hierarchical

Network

Relational

Object

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IST 210 Network model

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IST 210 Network data model

Relationships:

one-to-one one-to-many many-to-one many-to-many

Class

Student

Grade

Instructor

ID Department

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IST 210 Network data model

Advantages

flexible, fast, efficient

Disadvantages

Complex

Restructuring can be difficult because ofchanging all the pointers

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IST 210 Hierarchical database model

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IST 210 Hierarchical data model

Parent-child

relationship: one-to-one

one-to-many

Class

Student

Grade

Instructor

ID Department

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IST 210 Hierarchical data model

Advantages

easy to search

add new branches easily Disadvantages

Must establish the types of search prior to

development of the hierarchical structure

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IST 210 Summary

Hierarchical and network data models havegenerally been replaced by the relational data

model Relational databases dominate the database

market Oracle

Informix SQL Server

DB2

..

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IST 210 Relational database model

Stores both

Data about realworld objects(entities) intables

Relationships

between thetables

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IST 210 Relational database

Fields (columns) in thetable store attributes. Each attribute has a

specific domain.

Tuples (or records orrows) in the table storeinformation. Each tuple is a unique

instance of an object.

Tables are composed ofa set of tuples. A table is also called a

relation.

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IST 210 Records

Each record represents a logical entity (e.g. astudent)

Each field represents an attribute of thelogical entity

1 Wood Bob C IST357

2 Kent Chuck B IST115

3 Smith Jane A IST357

4 Boone Dan B IST357

ID Last First Grade Class

Student

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IST 210 Keys

Each table has a primary key, one field (or acombination of fields) that has a unique value foreach and every record in the table

IDis the primary keyin this table (two

students may shareeither a last or firstname)

1 Wood Bob C IST357

2 Kent Chuck B IST1153 Smith Jane A IST357



Student

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IST 210 Relating tables

Tables can be related (joined) together based on their keys The idea is to decompose into separate tables with no

redundancy and to provide a capability to reassemble with noinformation loss

1 Wood Bob C IST357

2 Kent Chuck B IST1153 Smith Jane A IST357



Student

IST357 48 Jones

IST115 120 Brower

IST20 120 Fountain

Class

Name #Stud Instructor

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1 Wood Bob C IST357





Student

IST357 48 Jones

IST115 120 Brower

IST20 120 Mennis

Class


Primary key Primary keyForeign key

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1 Wood Bob C IST357





Student

IST20 120 Brower

IST115 120 Jones

IST357 48 Jones

Class


Jones 332

Brower 517

Instructor

Name Office

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IST 210 DBMS Schema

Ultimately data in databases is stored infiles, but their structure is hidden

Conceptual Schema

External Schema

Internal Schema

The view on data used byapplication programs.

The logical model of data that is

separate from how it is used.

The physical storage of data infiles and indexes.

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IST 210 RDBMS Features

Data Definition Language(DDL)

Data Manipulation Language

(DML) Integrity Constraints

Transaction Management

Concurrency

Security Tuning of Storage

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IST 210 Data integrity and validation (Constraints)

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IST 210 Relationships

Link betweenentities.

A relationship maydefine constraints.

E.G, a person canonly have one SSN.

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IST 210 Advantages of RDBMS

Eliminate unnecessary duplication of data

Enforce data integrity through constraints

Changes to conceptual schema need not

affect external schema

Changes to internal schema need not affectthe conceptual schema

Many tools are available to manage thedatabase

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IST 210 Disadvantages of RDBMS

To store objects (e.g., drawings) in arelational database, the objects have to be

flattened into tables

e.g., a digital representation of a parcel must beseparated from the behaviour of other parcels

Complex objects have to be taken apart andthe parts stored in different tables

When retrieved from the database, the objecthas to be reassembled from the parts indifferent tables

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IST 210 Other Types of DBMS

Object DBMS

store objects as objects

designed to handle complex nested objectsfor graphical and multimedia applications

Object-relational DBMS

hybrid databases that can store data in

tables but can also store objects in tables

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IST 210 Object DBMS

ODBMS have theadvantage thatobjects can be

stored directly Object databases

are closely linkedto programminglanguages withways of navigatingthrough thedatabase

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IST 210 Summary

Commonword

Textbookword

Alternateword

Object word

Table Relation File or Data set

(old)

Object class

Column Attribute Field Object field

Domain Domain Range ofpossible values

Datatype,subtype

Row Tuple Record Object instance

Primary key Primary key Key of therecord

Object identifier

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