SALEH database lect2

8/6/2019 SALEH database lect2

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CS200 Database Systems

CS200 DATABASE SYSTEMS

LECTURE1INTRODUCTION

InstructorALLY .S. Nyamawe, [email protected] +255 715 016 580
mailto:[email protected]:[email protected]


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Cont...

chances are that our activities will involvesomeone or some computer program accessing adatabase. Even purchasing items from a

supermarket nowadays in many cases involvesan automatic update of the database that keepsthe inventory of supermarket items.

These interactions are examples of what we

may call traditional database applications, inwhich most of the information that is stored andaccessed is either textual or numeric.


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Database Definition

Databases and database technology are having amajor impact on the growing use of computers. Itis fair to say that databases play a critical role inalmost all areas where computers are used,including business, electronic commerce,engineering, medicine, law, education, and library

science, etc.Generally, A database is a collection of related

data.


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Cont...

By data, we mean known facts that can berecorded and that have implicit meaning. Forexample, consider the names, telephone numbers,

and addresses of the people you know. You mayhave recorded this data in an indexed address

book, or you may have stored it on a hard drive,using a personal computer and software such asMicrosoft Access, or Excel. This is a collection ofrelated data with an implicit meaning and hence isa database.


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Cont...

Also, A database can be defined as collection ofinformation organized in such a way that it canbe accessed easily.

ExamplesTracking customer ordersMaintaining Employees Records.Maintaining Students Information


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Database Properties

A database has the following implicit properties:A database represents some aspect of the real world,

sometimes called the miniworld or the universe ofdiscourse. Changes to the miniworld are reflected in

the database.A database is a logically coherent collection of data

with some inherent meaning. A random assortment ofdata cannot correctly be referred to as a database.

A database is designed, built, and populated with datafor a specific purpose. It has an intended group of usersand some preconceived applications in which theseusers are interested.


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History of Databases

Manual systems

File Processing Systems (FPS)

Database Management systems (DBMS)


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Manual Systems

Structure

Information can be stored in dedicated room or inseparate offices.

Room or office will be furnished with shelves.Different shelves will hold Records for different

subjects.

Records will be stored in hard flat files, each filewill carry one record.

Each file will have a specific number to identify it.

A person will use the file number to retrieve the

specific file (record).


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Manual Systems

User

File keeper

Files Cabinet


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Information stored as groups of records in separatefiles

File processing systems consisted of a few data filesand many application programs

Each file called a soft flat file

Flat file contain processed information for onespecific function

Use of programming languages to write applications

Little flexibility

High maintenance

Many limitations


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Limitations of File ProcessingSystems

Separate and isolated data.

Data redundancy.

Program - data interdependence involvingfile formats and access techniques.

Difficulty in representing data from theusers view.

Data inflexibility.


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Database Management systems(DBMS

A program that allows users to define, create,manipulate, store, maintain, retrieve, and process the

data in a database in order to produce meaningful

information.

Focus on information representationData stored as records in various database files that can

be combined to produce meaningful information for users

DBMS controls all functions of capturing, processing,

storing, retrieving data and generates various forms of dataoutput

Manages access by multiple users and multiple programsto a common store of data


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Cont..


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DBMS overcomes all Limitationsof FPS.

Eliminates separation and isolation of data

Reduces data redundancy

Eliminates dependence between programs and

data

Allows for representation of data from usersview

Increases data flexibilitySuperior flexibility and security over spreadsheet

applications


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Characteristics of a DBMS

Computerized record-keeping system

Contains facilities that allow the user to:

Add, delete files, Insert, retrieve, update,and delete data

Collection of databases; each can be used forseparate purposes or combined

Examples of DBMS are: Sql server, Ms Access,MySql, Oracle.


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Functions and Uses of a DBMS

To store data

To organize data

To control access to dataTo protect data

To provide decision support

To provide transaction processing


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Components of a DBMS

users/programmers

application programs/queries

software to process queries/programs

software to access stored data

stored database

definition

(meta -data)

stored

database


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Architecture of a DBMS

user queries

storage manager

stored database

definition

(meta-data)

stored

database

schema modifications modifications

query processor

transaction

manager


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Overview of DBMS Components

Stored Database and Meta-data: The stored databaseresides on secondary and tertiary devices. (At anygiven moment some portion of the database will also

be mirrored in cache, but we will ignore this for the

moment.)Meta-data is data about data. In this case the meta-data is

a description of the data components of the database.Offsets of fields within records. Typing information.

Schema information. Index information and so forth.For a given database, a DBMS may maintain many

different indices designed to provide fast access to randomdata.


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Cont...

Storage Manager: In a simple database system,the storage manager is nothing more than thefile system of the underlying OS. In larger

systems, for the purposes of efficiency, theDBMSs normally control storage on the diskdirectly.

The storage manager consists of two basiccomponents (1) the buffer manager, and (2) thefile manager.


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Cont...

File Manager: Keeps track of the location of files on the disksand obtains the block or blocks containing a file on requestfrom the buffer manager. Disks are typically blocked into

regions of contiguous space ranging between 212

and 214

bytes (between roughly 4000 to 16,000 bytes/block).

Buffer Manager: Handles main memory. It obtains blocks ofdata from the disk, via the file manager, and chooses a pageof main memory in which to store the block. The paging

algorithm will determine how long a page will remain inmain memory. However, the transaction manager can alsoforce a page in main memory to be returned to disk.


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Cont...

Query Manager: Turns a query or databasemanipulation, which may be expressed at avery high level (e.g., SQL) into a sequence

of request for stored data such as specifictuples of a relation or parts of an index to arelation.

Often the hardest part of query processing is

query optimization, which involves theformulation of a good query executionstrategy.


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Cont...

Transaction Manager: There are certain guarantees thata DBMS must make when performing operations on adatabase. These guarantees are often referred to as theACID properties.

Atomicity: all of a transaction is executed or none of itis executed.

Consistency: data cannot be in a inconsistent state.

Isolation: concurrent transactions must be isolated from

each other both in effect and in visibility.Durability: changes to the database caused by a

transaction must not be lost even if the system failsimmediately after the transaction completes.


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Database Design

For the system to be acceptable to the end-users, the database design activity is crucial.

A poorly designed database will generate

error that may lead to bad decisions beingmade, which may have serious repercussionsfor the organization. On the other hand, a well-

designed database produces, in an efficient way,a system that provides the correct informationfor the decision-making process to succeed.


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Roles in the Database Environment

Data and Database AdministratorsThe Data Administrator (DA) is responsible for the

management of the data resource including database planning, development and maintenance of standards,

policies and procedures, and conceptual/logical databasedesign.

The Database Administrator (DBA) is responsible for the physical realization of the database, including physicaldatabase design and implementation, security and integritycontrol, maintenance of the operational system, and ensuringsatisfactory performance of the applications for users. Therole of the DBA is more technically oriented than that of theDA.


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Database Administrator

A database administrator (DBA) controls andmanages the database.

Functions of a DBAMake decisions concerning the content of thedatabase

Plan storage structures and access strategies

Provides support to usersDefines security and integrity checks

Interprets backup and recovery strategies.

R l i th D t b E i t


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Roles in the Database Environment(Cont..)

Database DesignersIn large db design projects, we can distinguish between two

types of designers: logical database designers and physicaldatabase designers.

Logical database designers are concerned with identifyingthe data (the entities and attributes), the relationshipsbetween the data, and the constraints on the data that will bestored in the database.

Physical database designers are highly dependent on thetarget DBMS, and there may be more than one way ofimplementing a mechanism. The physical db designer mustbe fully aware of the functionality of the target DBMS.


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Cont...

Application DevelopersOnce the database has been implemented, the

application programs that provide the required

functionality for the end-users must beimplemented. This is the responsibility of theapplication developers.


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Cont...

End UsersEnd users are the clients for the database and can be

broadly categorized into two groups based upon how theyutilize the system.

Nave users are typically unaware of the DBMS.They access the database through specially writtenapplication programs which attempt to make theoperations as simple as possible. They typically knownothing about the database or the DBMS.

Sophisticated users are familiar with the structure ofthe database and the facilities offered by the DBMS. Theywill typically use a high-level query language like SQL to perform their required operations and may even write their

own application programs.

Advantages and Disadvantages


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Advantages and Disadvantagesof a DBMS

Advantages:Centralized data reduces management problemsData redundancy and consistency are controllable

Program - data interdependency is diminishedFlexibility of data is increased

More information from the same amount of data

Sharing of data

Improved data integrityImproved security

Enforcement of standards


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Cont...

Disadvantages:Reduction in speed of data access time

Requires special knowledgePossible dependency of application

programs to specific DBMS versions


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More DBMS Advantages

control of data redundancy economy of scale

data consistency

more information from same data

amount of data available

sharing of data

improved data integrity

improved data security

enforcement of standards

balance of conflicting requirements

improved data accessibility

increased productivity

improved maintenance

increased concurrency

improved backup and recovery

improved responsiveness


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More DBMS Disadvantages

complexity

size

cost of DBMSs

additional hardware costs

cost of conversion

performance (specific cases)

higher impact of failure

complexity

size

cost of DBMSs

additional hardware costs

cost of conversion

performance (specific cases)

higher impact of failure

Th L l f Ab t ti i


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Three-Levels of Abstraction in a

Database System

View 1View 1 View 2View 2 View nView n

user 1 user 2 user n

external level

Conceptual

Schema

Conceptual

Schema

conceptual level

internal level

physical data organization

Internal

Schema

Internal

Schema

dbdb

external to

conceptualmapping

conceptual to

internal

mapping


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The External Level

The external level is the users view of the database.This level describes that part of the database which is

relevant to each user.The external level consists of a number of different

external views of the db. Each user has a view of thereal world represented in a form that is familiar for thatuser.

The external view includes only those entities,

attributes, and relationships in the real world that theuser is interested in. Other entities, attributes, andrelationships may exist, but the user will be unaware thatthey even exist.


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The External Level Cont...

It is often the case that different external views willhave different representations of the same data.Example: one view may represent dates in the form of

(month, day, year) while another view may represent dates

in the form of (day, month, year).Some views may include derived or calculated data. Thisis data that is not actually stored in the database as such,

but created when needed.

Example: one view may need to see a persons age.However, this is probably not a stored value in the db sinceit would require daily updates. Rather, it is probablyderived from stored data representing the persons date of

birth and the current date.


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The Conceptual Level

The conceptual level is the community view of the database.This level describes whatdata is stored in the database and therelationships among the data.This is the level at which the logical structure of the entire

database as seen by the DBA is contained. It represents a

complete view of the data requirements of the organization that isindependent of any storage considerations.

The conceptual level supports each external view, in that anydata available to a user must be contained in, or derivable from,the conceptual level.

This level contains no storage-dependent details. For example, an entity may be defined as represented byan integer data type at this level, but the number of bytes itoccupies is not specified at this level.


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The Internal Level

The internal level represents the physicalrepresentation of the database on the computer. Thislevel describes howthe data is stored in the database.The internal level describes the physical

implementation necessary to achieve optimal runtimeperformance and storage space utilization.It covers the data structures and file organizations

used to store the data on the storage devices.

It interfaces with the OS access methods (filemanagement techniques for storing and retrievingdata records) to place the data on the storage devices,

build indexes, retrieve the data, and so on.

Th Ph i l L l


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The Physical Level

Below the internal level is the physical level that may bemanaged by the OS under the direction of the DBMS.

The functions of the DBMS and the OS at the physicallevel are not clear cut and will vary from system to

system.Some DBMSs take advantage of many of the OS access

methods, while others will use only the most basic onesand create their own file organizations.

The physical level below the DBMS consists of itemsonly the OS knows, such as exactly how the sequencing isimplemented and whether the fields of internal recordsare stored as contiguous bytes on the disk.

D t I d d


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Data Independence

One of the major objectives of the three-levelarchitecture is to provide data independence, whichmeans that the upper levels are unaffected by changesto lower levels.

There are two types of data independence: logicalandphysical.Logical data independence refers to the immunity of

the external schemas to changes in the conceptual

schema.Physical data independence refers to the immunityof the conceptual schema to changes in the internalschema.


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Data Independence(cont.)

View 1View 1 View 2View 2 View nView n

user 1 user 2 user n

external level

ConceptualSchema

ConceptualSchema

conceptual level

internal level

physical data organization

Internal

Schema

Internal

Schema

dbdb

logical data independence

physical data independence

D t b L


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Database Languages

A data sublanguage consists of two parts: a Data DefinitionLanguage (DDL) and a Data Manipulation Language (DML).The DDL is used to specify the database schema and the DML

is used to both read and update the database.These languages are called data sublanguages because they do

not include constructs for all computing needs such asconditional or iterative statements, which are provided by thehigh-level programming languages.Most DBMSs have a facility for embedding the sublanguage ina high-level programming language such as COBOL, Pascal,

C, C++, Java, or Visual Basic which is then called the hostlanguage.Most data sublanguages also provide a non-embedded or

interactive version of the language to be input directly from a

terminal.

D t D fi iti L (DDL)


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Data Definition Language (DDL)

A Data Definition Language is a language thatallows the DBA or user to describe and name theentities, attributes, and relationships required forthe application, together with any associated

integrity and security constraints.The result of the compilation/execution of the DDLstatements is a set of tables stored in special filescollectively referred to as the system catalog. Thesystem catalog is also commonly referred to as thedata dictionary ordata directory.

D t M i l ti L (DML)


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Data Manipulation Language (DML)

A Data Manipulation Language is a language thatprovides a set of operations to support the basic datamanipulation operations on the data held in thedatabase.

DML operations usually include the following: insertion of new data into the database. modification of data stored in the database. retrieval of data contained in the database. deletion of data from the database.The part of the DML that involves data retrieval iscalled aquery language.

DMLs (cont )


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DMLs (cont.)

DMLs are distinguished by their underlying retrievalconstructs. We can distinguish two basic types of DMLs:procedural and non-procedural.Procedural DMLs are languages in which the user informsthe system whatdata is required and exactly howto retrieve

that data. Non-procedural DMLs are languages in which the userinforms the system only ofwhatdata is required and leavesthe how to retrieve the data entirely up to the system.

It is common for procedural DMLs to be embedded in high-level programming languages.Procedural DMLs tend to be more focused on individual

records while non-procedural DMLs tend to operate on sets ofrecords.

Fourth Generation Languages


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Fourth Generation Languages

There is no consensus as to what constitutes a4GL. In essences it is a shorthand programminglanguage. What requires several hundred lines of

code in a 3GL will require only a few lines ofcode in a 4GL.3GLs are procedural while 4GLs are non-

procedural.

4GLs include spreadsheets and databaselanguages.

SQL and QBE are examples of 4GLs.

Types of Databases


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Types of Databases

Flat Databases

Relational Database

Flat Databases


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Flat Databases

A single kind of record with a fixed number offields.

a way of organizing all information in a single

table.

suitable for extremely simple databases.

inherit data redundancy

Relational Database


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Relational Database

Data stored in a collection of columns androws called a table, or a relation

Tables may be electronically linked via akey field containing common data

Easy to add, delete and modify the data

and the table structures

Relational Database


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Relational Database

Summary


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Summary

In this lecture we defined a database as a collection ofrelated data, where data means recorded facts. A typicaldatabase represents some aspect of the real world and isused for specific purposes by one or more groups of users.

A DBMS is a generalized software package forimplementing and maintaining a computerized database.The database and software together form a databasesystem. We identified several characteristics thatdistinguish the database approach from traditional file-

processing applications.We discussed about database history and it's types as wellas it's users (a DBA, DA etc).

Challenge


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Challenge

Discuss the capabilities that should be providedby a DBMS.

Discuss the main characteristics of the database

and how it differs from traditional file systems.Why would you choose a database system

instead of simply storing data in operating systemfiles? When would it make sense not to use a

database system?

Questions


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Questions

Documents

SALEH database lect2