1 databases and database management systems

7/30/2019 1 Databases and Database Management Systems

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DatabasesandDatabase Management Systems

Based on Chapters 1-2 inFundamentals of Database Systems

by Elmasri and Navathe, Ed. 4


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Introduction to Database Systems 2

NOTES

1 Basic Definitions

2 Example of a Database

3 Main Characteristics ofDatabase Technology

4 Additional Benefits ofDatabase Technology

5 When Not to Use aDBMS

6 Data Models6A. History of data

Models

7 Schemas versusInstances

8 Three-SchemaArchitecture

9 Data Independence

10 DBMS Languages11 DBMS Interfaces

12 DBMS ComponentModules13 Database System

Utilities14 Classification of DBMSs


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Types of Databases andDatabase Applications

Numeric and Textual Databases

Multimedia Databases(store images, audio

clips, and video streams digitally).

Geographic Information Systems (GIS) (store

and analyze maps, weather data and satellite

images)

Data Warehouses and Online analyticalprocessing (OLAP)

Real-time and Active Databases (control

industrial and manufacturing process)


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Database Management System

(DBMS)

Collection of interrelated data

Set of programs to access the data

DBMS contains information about a particular

enterprise DBMS provides an environment that is both

convenientand efficientto use.



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Database Management System (DBMS)

Database Applications: Banking: all transactions

Airlines: reservations, schedules

Universities: registration, grades

Sales: customers, products, purchases

Manufacturing: production, inventory, orders, supply chain

Human resources: employee records, salaries, tax deductions

Databases touch all aspects of our lives


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Purpose of Database System

In the early days, database applicationswere built on top of file systems

Drawbacks of using file systems to store

data: Data redundancy and inconsistency

Multiple file formats, duplication of information in different files

Difficulty in accessing data

Need to write a new program to carry out each new task

Data isolation multiple files and formats

Integrity problems

Integrity constraints (e.g. account balance > 0) become part of

program code

Hard to add new constraints or change existing ones


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Purpose of Database Systems(Cont.)

Drawbacks of using file systems (cont.) Atomicity of updates

Failures may leave database in an inconsistent state with partial

updates carried out

E.g. transfer of funds from one account to another should eithercomplete or not happen at all

Concurrent access by multiple users

Concurrent accessed needed for performance

Uncontrolled concurrent accesses can lead to inconsistencies

E.g. two people reading a balance and updating it at the sametime

Security problems

Database systems offer solutions to all the

above problems


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1.Basic Definitions

Database:

A collection of related data.

Data:

Known facts that can be recorded and have an

implicit meaning.


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Basic Definitions

Mini-world:

Some part of the real world about which data is

stored in a database.

For example, student grades and transcripts at auniversity.


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Basic Definitions

Database Management System(DBMS) :

A software package/ system to facilitate the

creation and maintenance of a computerized

database.


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Basic Definitions

Database System:

The DBMS software together with the data itself.

Sometimes, the applications are also included.

Database System

= Data + DBMS + (Program)


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A simplifieddatabasesystemenvironment.


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Typical DBMS Functionality (1/2)

Define a database :

in terms of data types, structures and constraints

Construct or Load the Database on a

secondary storage medium

Manipulating the database :

querying, generating reports, insertions, deletions

and modifications to its content Concurrent Processing and Sharing by a set

of users and programs yet, keeping all data

valid and consistent


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Typical DBMS Functionality (2/2)

Other features:

Protection or Security measures to prevent

unauthorized access

Active processing to take internal actions ondata

Presentation and Visualization of data


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2. Example of a Database(with a Conceptual Data Model)

Mini-world for the example:

Part of a UNIVERSITY environment.

Entities

Relationships


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Some mini-world entities:

STUDENTs

COURSEs

SECTIONs (of COURSEs)

(academic) DEPARTMENTs

INSTRUCTORs


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University database


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Some mini-world relationships:

SECTIONs are of specific COURSEs

STUDENTs take SECTIONs

COURSEs have prerequisite COURSEs INSTRUCTORs teach SECTIONs

COURSEs are offered by DEPARTMENTs

STUDENTs major in DEPARTMENTs


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NOTE:

The above could be expressed in the

ENTITY-RELATIONSHIP data model.


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3. Main Characteristics ofDatabase Technology

1) Self-contained nature of a database system

2) Insulation between programs and data

3) Data Abstraction

4) Support of multiple views of the data

5) Sharing of data and multiuser transaction

processing


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Self-contained nature of adatabase system

A DBMS catalogstores the description of thedatabase.

The description is called meta-data.

This allows the DBMS software to work withdifferent databases.


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Insulation between programs anddata

Called program-data independence.

Allows changing data storage structures and

operations without having to change the

DBMS access programs.


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Data Abstraction

A data model is used to hide storage details

and present the users with a conceptual view

of the database.


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Support of multiple views of thedata

Each user may see a different view of the

database, which describes only the data of

interest to that user.


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The STUDENT TRANSCRIPT view.


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Internal storage format for aSTUDENT record


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Sharing of data and multiusertransaction processing

allowing a set of concurrent users to retrieve

and to update the database.

Concurrency control within the DBMS

guarantees that each transactionis correctlyexecuted or completely aborted.

OLTP (Online Transaction Processing) is a

major part of database applications.


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4. Additional Benefits of DatabaseTechnology

Controlling redundancy in data storage and in development andmaintenance efforts.

Sharing of data among multiple users.

Restricting unauthorized access to data.

Providing multiple interfaces to different classes of users. Representing complex relationships among data.

Enforcing integrity constraintson the database.

Providing backupand recoveryservices.

Potential for enforcing standards.

Flexibility to change data structures.

Reduced application development time.

Availability of up-to-date information.

Economies of scale.


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Actors on the scene

Person involve day to day use of a database.

To define, construct and manipulates the DB.

Called as Actors on the scene.

1. DBA (Database Administrator )

Many people use the same resources.

Chief administrator to overseer's and manages

these resources. Primary resource is DB

Secondary resource is DBMS and related s/w.



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DBA is responsible to administrate these

resources.

Responsible for authorizing access to DB,

coordinating, monitoring its uses , acquiring s/w

and h/w resources.



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Database Designer

Identifying the data to be stored in DB.

Choosing appropriate structure to represent and

store this data. Communicate with DB user to understand their

request and create a design that meets these

requirement.



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End User

Access DB for querying, updating and generating

reports.

1. Casual end user Occasionally access DB

Use sophisticated DB query language.

Middle or high level mangers or other occasional

browser.



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Naive or parametric end user

Constantly querying and updating DB.

Using standard types of queries and updates called

canned transaction

Sophisticated end user

Engineers

Scientists

Business analysts Use DB to implement their applications to meet their

computer requirements



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Standalone user

Personal DB by using ready made program package.

Menu based or graphic base interface.



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System analysts and application

programmers (s/w engineers)

System analysts

Determine the requirements of end users especiallynave and parametric end user

Develop specification for canned transcation.

Application programmer

Implement specification as program. Test, debug, document and maintain these canned

transcation.



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Worker Behind the Scene

Work to maintain the DB system environment

but not actively interested in DB itself.

DBMS system designer and implementers Design and implement the DBMS modules and

interface as s/w packages.



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Tool developers

Design and implements tool.

s/w packages that facilitate DB modeling and

design. Improves performance.

Operators and maintenance personnel

Responsible for actual running and maintenance

of the H/W and S/W environments for DB system.


Hi t i l D l t f


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Historical Development ofDatabase Technology

Early Database Applications:

The Hierarchical and Network Models were

introduced in mid 1960s and dominated during

the seventies. A bulk of the worldwide database processing still

occurs using these models.


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Historical Development of DatabaseTechnology

Relational Model based Systems:

The model that was originally introduced in

1970 was heavily researched and

experimented with in IBM and theuniversities.

Relational DBMS Products emerged in the

1980s.

Historical Development of


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Historical Development ofDatabase Technology

Object-oriented applications:

OODBMSs were introduced in late 1980s and

early 1990s to cater to the need of complex data

processing in CAD and other applications. Their use has not taken off much.


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Historical Development of DatabaseTechnology

Data on the Web and E-commerceApplications:

Web contains data in HTML (Hypertext markup

language) with links among pages. This has given rise to a new set of applications

and E-commerce is using new standards like XML

(eXtended Markup Language).


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Extending Database capabilities

New functionality is being added to DBMSs inthe following areas:

Scientific Applications

Image Storage and Management Audio and Video data management

Data Mining

Spatial data management

Time Series and Historical Data Management


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5 When not to use a DBMS

Main inhibitors (costs) of using a DBMS

When a DBMS may be unnecessary

When no DBMS may suffice

Main inhibitors (costs) of using a


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Main inhibitors (costs) of using aDBMS:

High initial investment and possible need foradditional hardware.

Overhead for providing generality, security,

recovery, integrity, and concurrency control.

When a DBMS may be


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When a DBMS may beunnecessary:

If the database and applications are simple,well defined, and not expected to change.

If there are stringent real-time requirements

that may not be met because of DBMSoverhead.

If access to data by multiple users is notrequired.


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When no DBMS may suffice:

If the database system is not able to handlethe complexity of data because of modeling

limitations

If the database users need special operationsnot supported by the DBMS.


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6. Data Models

Data Model:

A set of concepts to describe the structure of a

database, and certain constraints that the

database should obey.


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6. Data Models

Data Model Operations:

Operations for specifying database retrievals and

updates by referring to the concepts of the data

model.

Operations on the data model may include basicoperationsand user-defined operations


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Categories of data models:

Conceptualdata models

(high-level, semantic)

Physicaldata models

(low-level, internal)

Logical(representational, Implementation)data models

(record-oriented)


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Conceptual data models

Provide concepts that are close to the waymany users perceive data.

Also called entity-based or object-based data

models. Use concepts such as entities, attributes and

relationship.


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Physical data models:

Provide concepts that describe details of howdata is stored in the computer.

storage structure

Define record formats, record orderings and accesspath.

Access path

Structure that makes the search for particular

database records efficient.


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Implementation data models:

Also called logical data model

Provide concepts that fall between the above

two, balancing user views with some

computer storage details.


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6A. HISTORY OF DATA MODELS

Relational Model

Network Model

Hierarchical Data Model

Object-oriented Data Model(s

Object-Relational Models


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Relational Model:

proposed in 1970 by E.F. Codd (IBM), firstcommercial system in 1981-82.

Now in several commercial products

DB2, ORACLE,

SQL Server,

SYBASE, INFORMIX.


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Object-Relational Models :

Most Recent Trend.

Started with Informix Universal Server.

Exemplified in the latest versions of Oracle-

10g, DB2, and SQL Server etc. systems.


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7. Schemas versus Instances

Database Schema: The description of a database.

Includes

descriptions of the database structure and the constraints that should hold on the

database.

Schema Diagram: A diagrammatic display of (some aspects of) a

database schema.


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Schema diagram for University database


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Database Instance: The actual data stored in a database at a

particular moment in time .

Also called database state(oroccurrence orsnapshot or instances).


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Database State: Refers to the content of a database at a moment

in time.

Initial Database State: Refers to the database when it is loaded

Valid State:

A state that satisfies the structure and constraintsof the database.


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8. Three-Schema Architecture

Proposed to support DBMS characteristics of: Program-data independence.

Support of multiple views of the data.

Use of catalog to store the database description(schema).


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8. Three-Schema Architecture

Defines DBMS schemas at three levels : Internal schema

Conceptual schema

External schemas


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The three-schema architecture.


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Conceptual schema

Conceptual schemaat the conceptual level todescribe the structure and constraints for the

whole database.

Hide the details of physical structure andconcentrates on describing entities, data

types, relationships, user operations and

constraints.

Uses a conceptual or an implementation

data model.


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External schemas

External schemasat the external level todescribe the various user views.

Usually uses the same data model as the

conceptual level.


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Three-Schema Architecture

Mappings among schema levels are alsoneeded.

Programs refer to an external schema, and

are mapped by the DBMS to the internalschema for execution.


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9 Data Independence

Logical Data Independence The capacity to change the conceptual schema

without having to change the external schemas

and their application programs.

Physical Data Independence

The capacity to change the internal schema

without having to change the conceptual schema.


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Data Independence

When a schema at a lower level is changed,only the mappings between this schema andhigher-level schemas need to be changed ina DBMS that fully supports data

independence. The higher-level schemas themselves are

unchanged.

Hence, the application programs need not bechanged since the refer to the externalschemas.


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10. DBMS Languages

Data Definition Language (DDL)

Data Manipulation Language (DML)

Data Control Language (DCL)


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Data Definition Language (DDL):

Used by the DBA and database designers tospecify the conceptual schema of adatabase.

In many DBMSs, the DDL is also used todefine internaland external schemas(views).

In some DBMSs, separate storage definition

language (SDL) and view definition language(VDL) are used to define internal and external

schemas.

Data Manipulation Language


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p g g(DML):

Used to specify database retrievals andupdates.

DML commands (data sublanguage) can be

embedded in a general-purpose programminglanguage (host language), such as C, COBOL,

PL/1 or PASCAL.

Alternatively, stand-alone DML commands can be

applied directly (query language).


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DBMS Languages

High Level or Non-procedural Languages: e.g., SQL, are set-oriented and specify what data

to retrieve than how to retrieve. Also called

declarative languages.

Low Level or Procedural Languages:

record-at-a-time; they specify how to retrieve

data and include constructs such as looping.


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11. DBMS Interfaces

Menu-based interfaces for web clients orbrowsing

Forms-based interfaces

Graphical user interfaces Natural language interfaces

Speech input and output

Interfaces for parametric users


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DBMS Interfaces

Interfaces for the DBA: Creating accounts, granting authorizations

Setting system parameters

Changing schemas or access path

Component modules of a DBMS and


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Component modules of a DBMS andtheir interactions.


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13. Database System Utilities

To perform certain functions such as: Loading data stored in files into a database.

Backing up the database periodically on tape.

Reorganizing database file structures. Report generation utilities.

Performance monitoring utilities.

Other functions, such as sorting , user monitoring ,

data compression , etc.


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Data dictionary / repository:

Used to store schema descriptions and otherinformation such as design decisions,application program descriptions, userinformation, usage standards, etc.

Active data dictionary is accessed by DBMSsoftware and users/DBA.

Passive data dictionary is accessed byusers/DBA only.


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14. Classification of DBMSs

Based on data model

Other classifications


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Based on the data model used:

Traditional: Relational,

Network,

Hierarchical. Emerging:

Object-oriented,

Object-relational.


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Other classifications:

Single-user (typically used with micro- computers)vs. multi-user (most DBMSs).

Centralized (uses a single computer with onedatabase) vs. distributed (uses multiple computers,

multiple databases) Distributed Database Systems have now come to be

known as client server based database systems becausethey do not support a totally distributed environment, butrather a set of database servers supporting a set of clients.

Example of a Datab

ase


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p

(with a Logical Data Model)

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