Lecture 1 Database Systems - Walailak...

DATABASE SYSTEMS Lecture 1: Introduction to DBs 1

Lecture 1

Database Systems

ITM661 – Database Systems

• T. Connolly, and C. Begg, “Database Systems: A Practical Approach to Design, Implementation, and Management”, 5th edition,

Addison-Wesley, 2009. 6th edition, Addison-Wesley, 2014, ISBN: 0-132-94326-3, (International Edition).

• R. Elmasri and S. B. Navathe, “Fundamentals of Database Systems”, 5th ed., Pearson, 2007, ISBN: 0-321-41506-X.


TextbooksDatabase Systems: A Practical Approach to Design,

Implementation, and Management

By T. Connolly, and C. Begg,

6th edition, Addison-Wesley, 2014

ISBN: 0-132-94326-3

OR

5th edition, Addison-Wesley, 2009

ISBN-10: 0-321-60110-6,

ISBN-13: 978-0-321-60110-0

Fundamentals of Database Systems

By R. Elmasri and S. B. Navathe,

6th edition, Pearson (Addison & Wesley), 2010,

ISBN: 0-136-08620-9

http://wps.pearsoned.co.uk/ema_uk_he_connolly_datasys_4


Office Hours and Grading Content

Database and applications;

Database system development lifecycle;

Data modeling;

Relational model;

Database languages;

Design methodology;

Normalization;

Monitoring and tuning the operational systems.

Grading: Attendance 8%

Assignment/project 20% (TT)

Project 12% (SB)

Class activities 10% (SB)

Midterm 25% (TT)

Final 25% (SB)

ITS322 - DBMSs Lecture 1: Introduction to DBs and DB Env. 4

Course Outline

DATABASE SYSTEMS 4Lecture 1: Introduction to DBs


Lecture 1 Introduction to

Databases Systems

ITM661 – Database Systems

• T. Connolly, and C. Begg, “Database Systems: A Practical Approach to Design, Implementation, and Management”, 5th edition,

Addison-Wesley, 2009. 6th edition, Addison-Wesley, 2014, ISBN: 0-132-94326-3, (International Edition).

• R. Elmasri and S. B. Navathe, “Fundamentals of Database Systems”, 5th ed., Pearson, 2007, ISBN: 0-321-41506-X.


Objectives

Some common uses of database systems

The characteristics of file-based systems

The problems with the file-based approach

The benefits of database approach

The meaning of the terms database, database

systems, database management system (DBMS)

The typical functions of a DBMS

The advantages and disadvantages of DBMSs


Objectives

The major components of the DBMS environment

The personnel involved in the DBMS environment

Difference between data administration and database administration

Types of database systems

System Catalog and Information Resource Dictionary System (IRDS)

Purposes and the origin of the 3-level database architecture

Concepts and types of data models

Functions and components of a DBMS


Data Versus Information

Data constitute building blocks of information

Information produced by processing data

Information reveals meaning of data

Good, timely, relevant information key to

decision making

Good decision making key to organizational

survival


Where is Database?

The database (DB) is now such an integral part our day-to-day life that often we are not aware we are using one.

Ex: supermarket, credit card, travel agent, library, insurance, security systems, university.First applications focused on clerical tasks

Requests for information quickly followed

File systems developed to address needs

Data organized according to expected use

Data Processing (DP) specialists computerized manual file systems


Types of Databases and DB Applications

Traditional Applications:

Numeric and Textual Databases

More Recent Applications:

Multimedia Databases

Geographic Information Systems (GIS)

Data Warehouses

Real-time and Active Databases

Many other applications


File-based Systems

The file-based system is the predecessor of the

database system. Decentralized

A collection of application programs that perform

services for the end users (e.g. reports).

Each program defines and manages its own data.

File-based systems were an early attempt to

computerize the manual filing system.

The related topics: storage, security, indexing,

cross-reference, processing


Simple File-based System


File-based Processing


File-based System Critique (I)

File-based System Data Management

Requires extensive programming in third-generation

language (3GL)

Time consuming

Makes ad hoc queries impossible

Leads to islands of information

Data Raw Facts

Field Group of characters with specific meaning

Record Logically connected fields that describe a person, place, or thing

File Collection of related records


File-based System Critique (II)

Data Dependence

File structure is defined in the program code.

Change in file‟s data characteristics requires

modification of data access programs

Must tell program what to do and how

Makes file systems cumbersome from programming

and data management views

Structural Dependence

Change in file structure requires modification of related

programs


File-based System Critique (III)

Field Definitions and Naming Conventions

Flexible record definition anticipates reporting requirements

Selection of proper field names important

Attention to length of field names

Use of unique record identifiers

Data Redundancy

Different and conflicting versions of same data

Results of uncontrolled data redundancy

Data anomalies

Data inconsistency


File-based System Critique (IV)

Separation and isolation of data

Each program maintains its own set of data. Users of

one program may be unaware of potentially useful data

held by other programs.

Incompatible file formats

Programs are written in different languages, and so

cannot easily access each others files.

Fixed Queries/Proliferation of application

programs

Programs are written to satisfy particular functions.

Any new requirement needs a new program.


Database Approach

Arose because:

Definition of data was embedded in application

programs, rather than being stored separately and

independently.

No control over access and manipulation of data

beyond that imposed by application programs.

Result - the database and Database Management

System (DBMS).


Database Management

Database is shared, integrated computer structure

housing:

End user data

Metadata

Database Management System (DBMS)

Manages Database structure

Controls access to data

Contains query language


Database

A shared collection of logically related data (and

a description of this data), designed to meet the

information needs of an organization.

System catalog (data dictionary or metadata)

provides the description of the data to enable

program–data independence.

Logically related data comprises entities,

attributes, and relationships of an organization's

information.


Database Systems & DBMS

Database System

A system that occupies a database as a basic storage

Provides the following advantages over file-based

systems

Eliminates inconsistency, data anomalies, data dependency,

and structural dependency problems

Stores data structures, relationships, and access paths

Database Management Systems (DBMS)

A software system that enables users to define, create,

and maintain the database and which provides

controlled access to this database.


Simplified Database System Environment


Database vs. File Systems


DBMS Manages Interaction


Database Management System (DBMS)


Typical DBMS Functionality

Define a particular database in terms of its data types,

structures, and constraints

Construct or Load the initial database contents on a

secondary storage medium

Manipulating the database:

Retrieval: Querying, generating reports

Modification: Insertions, deletions and updates to its content

Accessing the database through Web applications

Processing and Sharing by a set of concurrent users and

application programs – yet, keeping all data valid and

consistent


Typical DBMS Functionality

Other features:

Protection or Security measures to prevent

unauthorized access

“Active” processing to take internal actions on data

Presentation and Visualization of data

Maintaining the database and associated programs over

the lifetime of the database application

Called database, software, and system maintenance


Functions of a DBMS (I)

Data Storage, Retrieval and Update.

Must furnish users with the ability to store, retrieve,

and update data in the database.

A User-Accessible Catalog.

Must furnish a catalog in which descriptions of data

items are stored and which is accessible to users.

Transaction Support

Must furnish a mechanism to ensure that either

(1) all the updates corresponding to a given transaction are made

or

(2) none of them are made.


Functions of a DBMS (II)

Concurrency Control Services

Must furnish a mechanism to ensure that database is

updated correctly when multiple users are updating the

database concurrently.

Recovery Services

Must furnish a mechanism for recovering the database

in the event that the database is damaged in any way.

Authorization Services & Security management

Must furnish a mechanism to ensure that only

authorized users can access the database.


Functions of a DBMS (III)

Support for Data Communication

Must be capable of integrating with communication software.

Integrity Services & Security management Must furnish a means to ensure that both the data in the

database and changes to the data follow certain rules.

Services to Promote Data Independence

Must include facilities to support the independence of programs from the actual structure of the database.

Utility Services

Should provide a set of utility services.


Functions of a DBMS (IV)

Data transformation and presentation

Backup and recovery management

Database language and application

programming interfaces

A view mechanism.

Provides users with only the data they want

or need to use.


Components of a DBMS

1. Query processor

2. Database manager (DM)

3. File manager

4. DML preprocessor

5. DDL compiler

6. Catalog manager


Components of Database Manager (DM)

1. Authorization control

2. Command processor

3. Integrity checker

4. Query optimizer

5. Transaction manager

6. Scheduler

7. Recovery manager

8. Buffer manager


Advantages of Using DB Approach (I)

Controlling redundancy in data storage and in

development and maintenance efforts.

Sharing of data among multiple users.

Restricting unauthorized access to data.

Providing persistent storage for program Objects

Object-oriented DBMSs

Providing Storage Structures (e.g. indexes) for

efficient Query Processing


Advantages of Using DB Approach (II)

Providing backup and recovery services.

Providing multiple interfaces to different classes

of users.

Representing complex relationships among data.

Enforcing integrity constraints on the database.

Drawing inferences and actions from the stored

data using deductive and active rules


Additional Implications of DB Approach (I)

Potential for enforcing standards:

This is very crucial for the success of database

applications in large organizations.

Standards refer to data item names, display formats,

screens, report structures, meta-data (description of

data), Web page layouts, etc.

Reduced application development time:

Incremental time to add each new application is

reduced.


Additional Implications of DB Approach (II)

Flexibility to change data structures:

Database structure may evolve as new requirements are

defined.

Availability of current information:

Extremely important for on-line transaction systems

such as airline, hotel, car reservations.

Economies of scale:

Wasteful overlap of resources and personnel can be

avoided by consolidating data and applications across

departments.


Disadvantages of DBMS

Complexity

Size

Cost of DBMS

Additional hardware costs

Cost of conversion

Performance

Higher impact of a failure


When not to use a DBMS Main inhibitors (costs) of using a DBMS:

High initial investment and possible need for additional hardware.

Overhead for providing generality, security, concurrency control,

recovery, and integrity functions.

When a DBMS may be unnecessary:

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 DBMS overhead.

If access to data by multiple users is not required.

If the database system is not able to handle the complexity of data

because of modeling limitations

If the DB users need special operations not supported by the DBMS.


Example of a DB

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

Note: The above entities and relationships are typically

expressed in a conceptual data model, such as the

ENTITY-RELATIONSHIP data model (learn more later)


A Simple Database (I)


A Simple Database (II)


Main Characteristics of the DB Approach

Self-describing nature of a database system:

A DBMS catalog stores the description of a particular

database (e.g. data structures, types, and constraints)

The description is called meta-data.

This allows the DBMS software to work with different

database applications.

Insulation between programs and data:

Called program-data independence.

Allows changing data structures and storage organization

without having to change the DBMS access programs.


A Simplified Database Catalog


Main Characteristics of DB Approach (I)

Data Abstraction:

A data model is used to hide storage details and

present the users with a conceptual view of the

database.

Programs refer to the data model constructs rather

than data storage details

Support of multiple views of the data:

Each user may see a different view of the database,

which describes only the data of interest to that

user.


Main Characteristics of DB Approach (II)

Sharing of data and multi-user transaction

processing: Allowing a set of concurrent users to retrieve from and to

update the database.

Concurrency control within the DBMS guarantees that each

transaction is correctly executed or aborted

Recovery subsystem ensures each completed transaction has

its effect permanently recorded in the database

OLTP (Online Transaction Processing) is a major part of

database applications. This allows hundreds of concurrent

transactions to execute per second.


Hardware

Can range from a PC to a network of computers.

Software

DBMS, operating system, network software (if necessary) and also

the application programs.

Data

Used by the organization and a description of this data called the

schema.

Procedures

Instructions and rules that should be applied to the design and use

of the database and DBMS.

People

DBMS Environment(Major components)


Database Users Users may be divided into

Actors on the Scene

Those who actually use and control the database content,

and those who design, develop and maintain database

applications.

Data Administrator (DA)

Database Administrator (DBA)

Database Designers (Logical and Physical)

Application Programmers

End Users (native and sophisticated)

Workers Behind the Scene

Those who design and develop the DBMS software and

related tools, and the computer systems operators.


Users in DB System Environment


Data Administration vs. Database Administration

Data Administration

The management of the data resource, which includes

database planning, development and maintenance of

standards, policies and procedures, and conceptual and

logical database design.

Database Administration

The management of the physical realization of a

database application, which includes physical database

design and implementation, setting security and

integrity controls, monitoring system performance, and

reorganizing the database, as necessary.


Data Administration Tasks


Database Administration Tasks


DA and DBA – Main Task Differences.


Database System Types

Single-user vs. Multi-user Database

Desktop

Workgroup

Enterprise

Centralized vs. Distributed

Usage Purpose

Production or transactional

Decision support or data warehouse

Multi-user DBMS Architecture

Teleprocessing

File-server

Client-server


Teleprocessing

Traditional architecture.

Single mainframe with a number of terminals

Trend is now towards downsizing.


File-server

File-server is connected to several workstations

across a network.

Database resides on file-server.

DBMS and applications run on each workstation.

Disadvantages include:

Significant network traffic.

Copy of DBMS on each workstation.

Concurrency, recovery and integrity control more

complex.


File-server Architecture


Client-server

Server holds the database and the DBMS.

Client manages the user interface and runs

applications.

Advantages include:

Wider access to existing databases.

Increased performance.

Possible reduction in hardware costs.

Reduction in communication costs.

Increased consistency.


Client-server Architecture


Alternative Client-server Topologies


Summary of Client-server Functions


DBMS Server

Provides database query and transaction services to the clients

Relational DBMS servers are often called SQL servers, query servers, or transaction servers

Applications running on clients utilize an Application Program Interface (API) to access server databases via standard interface such as:

ODBC: Open Database Connectivity standard

JDBC: for Java programming access

Client and server must install appropriate client module and server module software for ODBC or JDBC


Two Tier Client-Server Architecture

A client program may connect to several DBMSs,

sometimes called the data sources.

In general, data sources can be files or other non-

DBMS software that manages data.

Other variations of clients are possible: e.g., in

some object DBMSs, more functionality is

transferred to clients including data dictionary

functions, optimization and recovery across

multiple servers, etc.


Three Tier Client-Server Architecture

Common for Web applications

Intermediate Layer called Application Server or Web

Server:

Stores the web connectivity software and the business logic part

of the application used to access the corresponding data from the

database server

Acts like a conduit for sending partially processed data between

the database server and the client.

Three-tier Architecture Can Enhance Security:

Database server only accessible via middle tier

Clients cannot directly access database server


Three-tier client-server architecture

Three-Tier Client-Server

Client side presented two problems preventing

true scalability:

„Fat‟ client, requiring considerable resources on client‟s

computer to run effectively.

Significant client side administration overhead.

By 1995, three layers proposed, each potentially

running on a different platform.

Pearson Education © 2014 66


Advantages:

„Thin‟ client, requiring less expensive hardware.

Application maintenance centralized.

Easier to modify or replace one tier without affecting others.

Separating business logic from database functions makes it

easier to implement load balancing.

Maps quite naturally to Web environment.


Transaction Processing Monitors

Program that controls data transfer between

clients and servers in order to provide a consistent

environment, particularly for Online Transaction

Processing (OLTP).

69Pearson Education © 2014

TPM as middle tier of 3-tier client-server



System Catalog

A repository of information (metadata) describing

the data in the database.

Typically stores:

Names of authorized users.

Names of data items in the database.

Constraints on each data item.

Data items accessible by a user and the type of access.

It is used by modules such as:

Authorization Control.

Integrity Checker.


Information Resource Dictionary System (IRDS)

Response to an attempt to standardize data dictionary

interfaces.

An IRDS is a software tool that can be used to control and

document an organization‟s information resources.

It provides a definition for the tables that comprise the

data dictionary and the operations that can be used to

access these tables.

Objectives:

Extensibility of data

Integrity of data

Controlled access to data


IRDS Services Interface


Three-Level Architecture of a DB system (Objective)

All users should be able to access same data.

A user's view is immune to changes made in other views.

Users should not need to know physical database storage

details.

DBA should be able to change database storage structures

without affecting the users' views.

Internal structure of database should be unaffected by

changes to physical aspects of storage.

DBA should be able to change conceptual structure of

database without affecting all users.


ANSI-SPARC Three-level Architecture


ANSI-SPARC Three-level Architecture

External Level

Users' view of the database. Describes that part of

database that is relevant to a particular user.

Conceptual Level

Community view of the database. Describes what data

is stored in database and relationships among the data.

Internal Level

Physical representation of the database on the

computer. Describes how the data is stored in the

database.


Difference between Three levels


Data Independence and the ANSI-SPARC 3-level Architecture


Data Independence

Logical Data Independence

The capacity to change the conceptual schema without having to

change the external schemas and their associated application

programs.

Conceptual schema changes e.g. addition/removal of entities.

Should not require changes to external schema or rewrites of

application programs.

Physical Data Independence

The capacity to change the internal schema without having to

change the conceptual schema.

Internal schema changes e.g. using different file organizations,

storage structures/devices.

Should not require change to conceptual or external schemas.


Historical Development of DB Tech. (I)

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, particularly, the hierarchical model.

Relational Model based Systems:

Relational model was originally introduced in 1970, was heavily

researched and experimented within IBM Research and several

universities.

Relational DBMS Products emerged in the early 1980s.


Historical Development of DB Tech. (II)

Object-oriented and emerging applications:

Object-Oriented Database Management Systems (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.

Many relational DBMSs have incorporated object database

concepts, leading to a new category called object-relational

DBMSs (ORDBMSs)

Extended relational systems add further capabilities (e.g. for

multimedia data, XML, and other data types)


Historical Development of DB Tech. (III)

Data on the Web and E-commerce Applications:

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).

Script programming languages such as PHP and JavaScript allow generation of dynamic Web pages that are partially generated from a database.

Also allow database updates through Web pages


Extending Database Capabilities

New functionality is being added to DBMSs in the following areas:

Scientific Applications

XML (eXtensible Markup Language)

Image Storage and Management

Audio and Video Data Management

Data Warehousing and Data Mining

Spatial Data Management

Time Series and Historical Data Management

The above gives rise to new research and development in incorporating new data types, complex data structures, new operations and storage and indexing schemes in database systems.


Data Models (I)

Data Model:

A set of concepts to describe the structure of a database, the

operations for manipulating these structures, and certain

constraints that the database should obey.

Data Model Structure and Constraints:

Constructs are used to define the database structure

Constructs typically include elements (and their data types)

as well as groups of elements (e.g. entity, record, table), and

relationships among such groups

Constraints specify some restrictions on valid data; these

constraints must be enforced at all times


Data Models (II)

Collection of concepts for describing data, relationships

between data and constraints on the data in an

organization.

Data Model comprises:

A structural part

Consisting of a set of rules according to which databases can be

constructed.

A manipulative part

Defining the types of operations that are allowed on the data

(update/retrieving data from the DB or changing the DB structure).

Possibly a set of integrity rules

Ensuring that the data is accurate.


Data Models (III)

Data Model Operations:

These operations are used for specifying database

retrievals and updates by referring to the constructs of

the data model.

Operations on the data model may include basic model

operations (e.g. generic insert, delete, update) and user-

defined operations (e.g. compute_student_gpa,

update_inventory)


Data Models (IV) – Levels of Data Models

Conceptual (high-level, semantic) data models:

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

(Also called entity-based or object-based data models.)

Physical (low-level, internal) data models:

Provide concepts that describe details of how data is stored in the

computer.

These are usually specified in an ad-hoc manner through DBMS

design and administration manuals

Implementation (representational, logical) data models:

Provide concepts that fall between the above two, used by many

commercial DBMS implementations (e.g. relational data models

used in many commercial systems).


Data Models (V) – Types of Data Models

Types of Data Models

Record-based Data Models

Object-based Data Models

Physical Data Models

The first two models are used to describe data at

the conceptual and Logical levels, the latter is for

the internal level.


Data Models (VI)

Record-based Data Models Hierarchical Data Model

Network Data Model

Relational Data Model

Object-based Data Models Entity-Relationship

Object-Oriented

Semantic or Functional

Physical Data Models Physical data models describe how data is stored in the computer,

representing information such as record structures, record orderings, and access paths

There are not as many physical data models as logical data models, the most common ones being the unifying model and the frame memory


Implementation Data Models

1st generation

2nd generation

3nd generation


Hierarchical Data Model (I)

Initially implemented in a joint effort by IBM and

North American Rockwell around 1965. Resulted in

the IMS family of systems.

IBM‟s IMS product had (and still has) a very large

customer base worldwide

Hierarchical model was formalized based on the IMS

system

Other systems based on this model: System 2k (SAS

inc.)


Hierarchical Data Model (II)

Logically represented by an upside down tree Each parent can have many children

Each child has only one parent


Hierarchical Data Model (III)

Advantages:

Conceptual simplicity, simple to construct and operate

Corresponds to a number of natural hierarchically

organized domains, e.g., organization (“org”) chart

Language is simple:

Uses constructs like GET, GET UNIQUE, GET NEXT,

GET NEXT WITHIN PARENT, etc.

Database security and integrity, Data independence,

Efficiency


Hierarchical Data Model (IV)

Disadvantages:

Navigational and procedural nature of processing

Database is visualized as a linear arrangement of

records

Little scope for "query optimization“

Complex implementation, programming and use

complexity

Difficult to manage and lack of standards

Lacks structural independence

Implementation limitations


Network Data Models (I)

The first network DBMS was implemented by

Honeywell in 1964-65 (IDS System).

Adopted heavily due to the support by CODASYL

(Conference on Data Systems Languages)

(CODASYL - DBTG report of 1971).

Later implemented in a large variety of systems -

IDMS (Cullinet - now Computer Associates), DMS

1100 (Unisys), IMAGE (H.P. (Hewlett-Packard)),

VAX -DBMS (Digital Equipment Corp., next

COMPAQ, now H.P.).


Network Data Model (II)

Each record can have multiple parents Composed of sets

Each set has owner record and member record

Member may have several owners


Network Data Model (III) – Another Example


Network Data Model (IV)

Advantages:

Able to model complex relationships and represents semantics of add/delete on the relationships.

Can handle most situations for modeling using record types and relationship types.

Language is navigational; uses constructs like FIND, FIND member, FIND owner, FIND NEXT within set, GET, etc.

Programmers can do optimal navigation through the database.

Conceptual simplicity

Data access flexibility

Promotes database integrity

Data independence

Conformance to standards


Network Data Model (V)

Disadvantages:

Lack of structural independence

Navigational and procedural nature of processing

System complexity, Database contains a complex array

of pointers that thread through a set of records.

Little scope for automated “query optimization”


Relational Data Model (I)

Proposed in 1970 by E.F. Codd (IBM), first commercial

system in 1981-82.

Now in several commercial products (e.g. DB2,

ORACLE, MS SQL Server, SYBASE, INFORMIX).

Several free open source implementations, e.g. MySQL,

PostgreSQL

Currently most dominant for developing database

applications.

SQL relational standards: SQL-89 (SQL1), SQL-92

(SQL2), SQL-99, SQL3, …


Relational Data Model (II)

Represented by a collection of tables (row/column)

Tables related by sharing common entity characteristic(s)


Relational Data Model (III)

Advantages

Structural independence

Improved conceptual simplicity

Easier database design, implementation, management, and use

Ad hoc query capability with SQL

Powerful database management system

Disadvantages

Substantial hardware and system software overhead

Poor design and implementation is made easy

May promote “islands of information” problems


Entity Relationship Data Model

Complements the relational data model concepts

Represented in an entity relationship diagram (ERD)

Based on entities, attributes, and relationships


Entity Relationship Data Model

Advantages

Exceptional conceptual simplicity

Visual representation

Effective communication tool

Integrated with the relational database model

Disadvantages

Limited constraint representation

Limited relationship representation

No data manipulation language

Loss of information content


Object-Oriented Data Model (I)

Several models have been proposed for implementing in a

database system.

One set comprises models of persistent O-O

Programming Languages such as C++ (e.g., in

OBJECTSTORE or VERSANT), and Smalltalk (e.g., in

GEMSTONE).

Additionally, systems like O2, ORION (at MCC - then

ITASCA), IRIS (at H.P.- used in Open OODB).

Object Database Standard: ODMG-93, ODMG-version

2.0, ODMG-version 3.0.


Object-Oriented Data Model (II)

Objects or abstractions of real-world entities are

stored

Attributes describe properties

Collection of similar objects is a class

Methods represent real world actions of classes

Classes are organized in a class hierarchy

Inheritance is ability of object to inherit attributes and

methods of classes above it


Object-Oriented Data Model (III)

Advantages

Adds semantic content

Visual presentation includes semantic content

Database integrity

Both structural and data independence

Disadvantages

Lack of OODM

Complex navigational data access

Steep learning curve

High system overhead slows transactions


OO Model vs. ER Model


Object-Relational Data Model

Most Recent Trend. Started with Informix

Universal Server.

Relational systems incorporate concepts from

object databases leading to object-relational.

Exemplified in the latest versions of Oracle-10i,

DB2, and SQL Server and other DBMSs.

Standards included in SQL-99 and expected to be

enhanced in future SQL standards.


Database Languages

Data definition language (DDL)

Permits specification of data types, structures and any data

constraints. All specifications are stored in the database.

Allows users to describe and name entitles, attributes and

relationships required for the application.

Data manipulation language (DML)

General enquiry facility (query language) of the data.

Provides basic data manipulation operations on data held in the

database.

Procedural DML - allows user to tell system exactly how to

manipulate data.

Non-Procedural DML - allows user to state what data is needed

rather than how it is to be retrieved.


Database Languages

Fourth Generation Language (4GL)

Query Languages

Forms Generators

Report Generators

Graphics Generators

Application Generators

There is no consensus about what constitutes a 4GL.

Compared with a 3GL, which is procedural, a 4 GL is

non-procedural.

The user defines what is to be done, not how.


DBMS Languages (DDL vs. DML)

Data Definition Language (DDL):

Used by the DBA and database designers to specify the

conceptual schema of a database.

In many DBMSs, the DDL is also used to define

internal and external schemas (views).

In some DBMSs, separate storage definition language

(SDL) and view definition language (VDL) are used to

define internal and external schemas.

SDL is typically realized via DBMS commands provided to

the DBA and database designers


DBMS Languages

Data Manipulation Language (DML):

Used to specify database retrievals and updates

DML commands (data sublanguage) can be embedded

in a general-purpose programming language (host

language), such as COBOL, C, C++, or Java.

A library of functions can also be provided to access the

DBMS from a programming language

Alternatively, stand-alone DML commands can be

applied directly (called a query language).


Types of DML

High Level or Non-procedural Language:

For example, the SQL relational language

Are “set”-oriented and specify what data to retrieve

rather than how to retrieve it.

Also called declarative languages.

Low Level or Procedural Language:

Retrieve data one record-at-a-time;

Constructs such as looping are needed to retrieve

multiple records, along with positioning pointers.


DBMS Interfaces

Stand-alone query language interfaces

Example: Entering SQL queries at the DBMS

interactive SQL interface (e.g. SQL*Plus in ORACLE)

Programmer interfaces for embedding DML in

programming languages

User-friendly interfaces

Menu-based, forms-based, graphics-based, etc.

Middleware

Middleware is a generic term used to describe

software that mediates with other software and

allows for communication between disparate

applications in a heterogeneous system.

The need for middleware arises when

distributed systems become too complex to

manage efficiently without a common

interface.

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Cloud Computing

The National Institute of Standards and

Technology (NIST) provided a definition.

Defined as “A model for enabling ubiquitous,

convenient, on-demand network access to a

shared pool of configurable computing

resources (e.g. networks, servers, storage,

applications, and services) that can be rapidly

provisioned and released with minimal

management effort or service provider

interaction.”

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Transaction Processing Monitors TP monitor is a program that controls data transfer between

clients and servers in order to provide a consistent environment,

particularly for online transaction processing (OLTP).

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Web Services and Service-Oriented Architectures

Web service is a software system designed to

support interoperable machine-to-web service

machine interaction over a network.

Web services share business logic, data, and

processes through a programmatic interface

across a network.

Developers can add the Web service to a Web

page (or an executable program) to offer

specific functionality to users.

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Web Services/Service-Oriented Architectures

Web services approach uses accepted

technologies and standards, such as:

XML (extensible Markup Language).

SOAP (Simple Object Access Protocol) is a

communication protocol for exchanging structured

information over the Internet and uses a message

format based on XML. It is both platform- and

language-independent.

WSDL (Web Services Description Language) protocol,

again based on XML, is used to describe and locate a

Web service.

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Web Services/Service-Oriented Architectures

UDDI (Universal Discovery, Description, and

Integration) protocol is a platform independent, XML-

based registry for businesses to list themselves on the

Internet.

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Service-Oriented Architectures (SOA)

A business-centric software architecture for

building applications that implement business

processes as sets of services published at a

granularity relevant to the service consumer.

Services can be invoked, published, and

discovered, and are abstracted away from the

implementation using a single standards-based

form of interface.

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Distributed DBMSs

A distributed database is a logically

interrelated collection of shared data (and a

description of this data), physically distributed

over a computer network.

A distributed DBMS is the software system

that permits the management of the

distributed database and makes the

distribution transparent to users.

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Distributed DBMSs

A DDBMS consists of a single logical database

split into a number of fragments.

Each fragment is stored on one or more computers

(replicas) under the control of a separate DBMS,

with the computers connected by a network.

Each site is capable of independently processing

user requests that require access to local data (that

is, each site has some degree of local autonomy)

and is also capable of processing data stored on

other computers in the network.

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Data Warehousing

A data warehouse was deemed the solution to meet the

requirements of a system capable of supporting decision

making, receiving data from multiple operational data sources.

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Cloud Computing

The National Institute of Standards and

Technology (NIST) provided a definition.

Defined as “A model for enabling ubiquitous,

convenient, on-demand network access to a

shared pool of configurable computing

resources (e.g. networks, servers, storage,

applications, and services) that can be rapidly

provisioned and released with minimal

management effort or service provider

interaction.”

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Cloud Computing – Key Characteristics

On-demand self-service

Consumers can obtain, configure and deploy cloud

services without help from provider.

Broad network access

Accessible from anywhere, from any standardized

platform (e.g. desktop computers, laptops, mobile

devices).

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Resource pooling

Provider’s computing resources are pooled to serve

multiple consumers, with different physical and

virtual resources dynamically assigned and

reassigned according to consumer demand.

Examples of resources include storage, processing,

memory, and network bandwidth.

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Rapid elasticity

Provider’s capacity caters for customer’s spikes in

demand and reduces risk of outages and service

interruptions. Capacity can be automated to scale

rapidly based on demand.

Measured service

Provider uses a metering capability to measure

usage of service (e.g. storage, processing,

bandwidth, and active user accounts).

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Cloud Computing – Service Models

Software as a Service (SaaS):

Software and data hosted on cloud. Accessed

through using thin client interface (e.g. web

browser). Consumer may be offered limited user

specific application configuration settings.

Examples include Salesforce.com sales management

applications, NetSuite’s integrated business

management software, Google’s Gmail and

Cornerstone OnDemand.

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Platform as a Service (PaaS)

Allows creation of web applications without

buying/maintaining the software and underlying

infrastructure. Provider manages the

infrastructure including network, servers, OS and

storage, while customer controls deployment of

applications and possibly configuration.

Examples include Salesforce.com’s Force.com,

Google’s App Engine, and Microsoft’s Azure.

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Infrastructure as a Service (IaaS)

Provider’s offer servers, storage, network and

operating systems – typically a platform

virtualization environment – to consumers as an on-

demand service, in a single bundle and billed

according to usage.

A popular use of IaaS is in hosting websites.

Examples Amazon’s Elastic Compute Cloud (EC2),

Rackspace and GoGrid.

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Cloud Computing – Comparison of Services

Models

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Benefits of Cloud Computing

Cost-Reduction: Avoid up-front capital expenditure.

Scalability/Agility: Organisations set up resources on an as-

needs basis.

Improved Security: Providers can devote expertise &

resources to security; not affordable by customer.

Improved Reliability: Providers can devote expertise &

resources on reliability of systems; not affordable by

customer.

Access to new technologies: Through use of provider’s

systems, customers may access latest technology.

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Benefits of Cloud Computing

Faster development: Provider’s platforms can

provide many of the core services to accelerate

development cycle.

Large scale prototyping/load testing: Providers

have the resources to enable this.

More flexible working practices: Staff can access

files using mobile devices.

Increased competitiveness: Allows organizations to

focus on their core competencies rather than their

IT infrastructures.

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Risks of Cloud Computing

Network Dependency: Power outages, bandwidth issues and

service interruptions.

System Dependency: Customer’s dependency on

availability and reliability of provider’s systems.

Cloud Provider Dependency: Provider could became

insolvent or acquired by competitor, resulting in the

service suddenly terminating.

Lack of control: Customers unable to deploy technical or

organisational measures to safeguard the data. May result

in reduced availability, integrity, confidentiality,

intervenability and isolation.

Lack of information on processing transparency

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Cloud-based database solutions

As a type of Software as a Service (SaaS),

cloud-based database solutions fall into two

basic categories:

Data as a Service (DaaS) and

Database as a Service (DBaaS).

• Key difference between the two options is

mainly how the data is managed.

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DBaaS

Offers full database functionality to application

developers.

Provides a management layer that provides

continuous monitoring and configuring of the

database to optimized scaling, high availability,

multi-tenancy (that is, serving multiple client

organizations), and effective resource allocation in

the cloud, thereby sparing the developer from

ongoing database administration tasks.

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DaaS:

Services enables data definition in the cloud and

subsequently querying.

Does not implement typical DBMS interfaces (e.g.

SQL) but instead data is accessed via common APIs.

Enables organization with valuable data to offer

access to others. Examples Urban Mapping

(geography data service), Xignite (financial data

service) and Hoovers (business data service.)

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Multi-tenant cloud database-shared server,

separate database server process architecture.

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Multi-tenant cloud database-shared DBMS

server, separate databases.

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Multi-tenant cloud database-shared DBMS

server, separate databases.

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Multi-tenant cloud database–shared database,

separate schema architecture.

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A DBMS is partitioned into several software

components (or modules), each of which is

assigned a specific operation. As stated

previously, some of the functions of the DBMS

are supported by the underlying operating

system.

The DBMS interfaces with other software

components, such as user queries and access

methods (file management techniques for

storing and retrieving data records).

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Components of a DBMS (Continued)

Query processor is a major DBMS component

that transforms queries into a series of low-

level instructions directed to the database

manager.

Database manager (DM) interfaces with user-

submitted application programs and queries.

The DM examines the external and conceptual

schemas to determine what conceptual records

are required to satisfy the request. The DM

then places a call to the file manager to

perform the request.

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File manager manipulates the underlying

storage files and manages the allocation of

storage space on disk. It establishes and

maintains the list of structures and indexes

defined in the internal schema.

DML preprocessor converts DML statements

embedded in an application program into

standard function calls in the host language.

The DML preprocessor must interact with the

query processor to generate the appropriate

code.

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DDL compiler converts DDL statements into a

set of tables containing metadata. These tables

are then stored in the system catalog while

control information is stored in data file

headers.

Catalog manager manages access to and

maintains the system catalog. The system

catalog is accessed by most DBMS components.

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Components of DB Manager (DM)

Components of the DB Manager

Authorization control to confirm whether the

user has the necessary permission to carry out

the required operation.

Command processor on confirmation of user

authority, control is passed to the command

processor.

Integrity checker ensures that requested

operation satisfies all necessary integrity

constraints (e.g. key constraints) for an

operation that changes the database.

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Query optimizer determines an optimal strategy

for the query execution.

Transaction manager performs the required

processing of operations that it receives from

transactions.

Scheduler ensures that concurrent operations

on the database proceed without conflicting

with one another. It controls the relative order

in which transaction operations are executed.

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Recovery manager ensures that the database

remains in a consistent state in the presence of

failures. It is responsible for transaction

commit and abort.

Buffer manager responsible for the transfer of

data between main memory and secondary

storage, such as disk and tape.

The recovery manager and the buffer manager

also known as (aka) the data manager. The

buffer manager aka the cache manager.

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