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Data

Data is a collection of facts, such as values or measurements.

It can be numbers, words, characters, symbols,measurements, observations or even just descriptions ofthings.

Data is the lowest level of abstraction, information is the nextlevel, and finally, knowledge is the highest level among allthree

Data on its own carries no meaning. For data to becomeinformation, it must be interpreted and take on a meaning by

a human or machine.

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Why data matters

As organizations continue to struggle to maintain competitiveadvantage, information becomes the key component inenabling executives and decision makers to make informeddecisions based on a 360-degree view of the organizationand its various operational processes.

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Data files

Each application generates a specific file type Read by an identical application produced by the

same vendor. Some applications do have import and export

facilities to allow a range of different formats tobe produced or read,

The specific issues with any data file relate tothe following:

-Version number of the application-Structure of data

e.g. student data file in an institute

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Data Processing

Data processing is the act of handling or manipulating data insome fashion.Regardless of the activities involved in it,

processing tries to assign meaning to data. Thus, the ultimate

goal of processing is to transform data into information.

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Information

Knowledge derived from study, experience (bythe senses), or instruction.

Communication of intelligence.

"Information is any kind of knowledge that isexchangeable amongst people, about things,facts, concepts, etc., in some context." *

"Information is interpreted data" (Data operatedin such a way as to display information)

e.g. if student is new to institute or not

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Why Information?

Information is critical

Information is a resource

-It is scarce

-It has a cost

-It has alternative uses

-cost factor involved if one does not process

information Ensure effective and efficient decision making

leading to prosperity of organization

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DATA

INFORMATION

KNOWLEDGE

Levels of Abstraction of Data , Information and

Knowledge

"Information is

interpreted data"

Raw Facts

Knowledge derived fromstudy, experience (by

the senses)

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Qualitative vs Quantitative Data

Data can be qualitative or quantitative.

Qualitative data is descriptive information (it describes something).

Quantitative data, is numerical information (numbers).

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Variables

Variables hold or store DataBasic Types of variables

Logical

Numeric - Integer, Float String or Text Variable

Mixed Variables (Data Structures)

- Complex data structures. To store records ofmixed types.Eg: AXEMP001 (Alphanumeric), Sailesh Singh (Text),20,000 (Numeric)

10(Numeric)

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Data files

Data Storage Flat files Data Base Management Systems

Flat files

Plain text fileBefore 1960s, when the concept of DBMS

was not there, flat text files were used as

databases, and programmers wroteprograms to store or retrieve data indata files

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Advantages of files as databases

Cheap - Using a flat file database costs practically nothing because data is storedas text files. No software is required other than the program that needs to accessthe data.

Platform Independent - Since text files are universally accepted by all serverplatforms, there is no problem moving your database from one server to another.

Very Simple to Understand - Records in a flat file are stored in one straight lineand are separated by delimiters.

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Disadvantages of Using FlatFiles

: Low Security - No security feature is built into a textfile. It can be opened for viewing by anyone whohappens to know where to look.

Data Redundancy- Duplication of same data indifferent files.- Wastage of storage space, since duplicated data isstored.-Errors may be generated due to updating of the same

data in different files.-Time in entering data again and again is wasted.-Computer Resources are needlessly used.-It is very difficult to combine information

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Data Inconsistency- Conflicting data in files.

(Example)

Suppose that in STUDENT file it is indicated that Roll no= 10

has opted for 'Computer course but in RESULT file it isindicated that Roll No. =10 has opted for 'Accounts' course.

Low Reliability & Integrity - Flat files are very prone to data

corruption especially if the size of the database grows beyondwhat the server resources are prepared to handle.

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Limited Data Structuring - As mentionedpreviously, records are stored as lines of text.This does not offer the flexibility of creating"relationships" between data whether within oneflat file or across several.

Difficult to Integrate with Other Programs -Once a flat file is created for use by oneprogram, it is impossible to have anotherprogram use it. This is because the succeedingprograms need to conform to the structure of theflat file

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What Is a DBMS?

Database - A very large, integrated collection

of data or facts. E.g.The information in aphone book is an example of a database.The database is the information stored on thepages of the book, not the book itself

A Database Management System (DBMS)isa software package designed to store andmanage databases. Typical examples of

DBMSs include Oracle, Microsoft Access,

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Advantage of DatabaseTechnology

Redundancy controlled (normalization)Efficientdata processing and storage

Data integrity and avoid inconsistencies

Integrity constraints Sharing data by many applications- Good fordecision support system

Data security

Standards can be enforced in datarepresentation, naming of variables anddocumentation

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Advantage of DatabaseTechnology

Data centralization- Shared by manydepartments

Data independence-Changes in structureof data files do not affect applicationprogram

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Disadvantage of DatabaseTechnology

Complex- Database administrator requiredfor maintenance

Costly to purchase and install

Since it is centralized high impact onorganization because of failure

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Structure of a DBMS

A typical DBMS has alayered architecture.

The figure does not

show the concurrencycontrol and recoverycomponents.

This is one of several

possible architectures;each system has itsown variations.

Query Optimizationand Execution

Relational Operators

Files and Access Methods

Buffer Management

Disk Space Management

DB

These layers

must consider

concurrency

control andrecovery

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Department Technician

Employees Equipment

Maintenance

Records

RDBMS

Model

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Motivation: Why databasemanagementsystems?

Database management systems (DBMSs)are very good at organizing and managinglarge collections of persistent data.

e.g. finding a particular book in a typicaluniversity library if the library does notkeep the books arranged in any particular

order or if the library has no indexes.

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Using a big collection of unorganizedthings is practically impossible. Structureturns data into information.

Persistencemeans that the data existpermanently; they do not disappear whenthe computer is shut off.

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Shift from computationto information

at the low end? scramble to webspace (amess!)

at the high end? scientific applications

Datasets increasing in diversity and volume.

Digital libraries, interactive video, Human

Genome project.

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DBMSs : data all in one place and easy to get to.

DBMSs help protect data from unauthorizedaccess

DBMSs help protect data from accidentalcorruption or loss due to:

-hardware failures such as power outages and

computer crashes-software failures such as operating systemcrashes

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Motivation: Why relational databasemanagement systems?

Concurrency Control

DBMSs allow concurrent access, meaning that asingle data set can be accessed by more than

one user at a time virtually all commercial database applications

require the data entry staff to have access to thedatabase simultaneously. E.g. an airlinereservation system cannot restrict access to thedatabase to a single travel agent.

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These problems can cause the databaseto be corrupted or for a users interfaceprogram to never complete its query.

e.g. if there are no traffic lights or stopsigns -chaos

RDBMSs provide mechanisms to prevent

concurrent access problems; thesemechanisms are collectively calledconcurrency control.

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Concurrent data access introducesunwanted problems caused by two usersmanipulating exactly the same data at

exactly the same time.

Logical data independence: Protectionfrom changes in logicalstructure of data.

Physical data independence: Protectionfrom changes in physicalstructure of data.

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Distributed RDBMS

A distributedDBMS allows a single database tobe split apart such that its pieces reside atgeographically separated sites.

this can provide performance improvements byeliminating transmitting the data across arelatively slow long distance communicationchannel (its a lot faster to have the database onhard drive than to access it across an Ethernetor via a modem)

this can reduce concurrency control problems bygiving each user that part of the database whichthey need rather than having all the userscompete for access to the whole database

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RDBMS characteristics

RDBMSs are not necessarily meant for dataanalysis; that is more the job of a spread sheetor some other special-purpose analysis tool.

RDBMSs are general-purpose tools. It isbasically irrelevant to the DBMS what is storedwithin it. Software design principles suggest de-coupling domain specific analysis packagesfrom the DBMS to keep the division of laborclear.

RDBMSs are very good at retrieving a relativelysmall portion of the database and passing italong for detailed analysis by a tool designed forthat purpose.

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RDBMS characteristics

RDBMSs often allow integrity constraints to be imposedon the data to insure validity and consistency. When anintegrity constraint applies to a table, all data in the tablemust conform to the corresponding rule.

E.g. TABLE Dept .ADD PRIMARY KEY (Deptno); Then,create a rule that every department listed in theemployee table must match one of the values in thedepartment table: alter table Emp ADD FOREIGN KEY(Deptno) REFERENCES Dept_tab (Dept no); When you

add a new employee record to the table, automaticcheck that its department number appears in thedepartment table

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Referential Integrity Rules

A rule defined on a key (a column or set of columns) inone table that guarantees that the values in that keymatch the values in a key in a related table (thereferenced value).

Referential integrity also includes the rules that dictatewhat types of data manipulation are allowed onreferenced values and how these actions affectdependent values. The rules associated with referentialintegrity are:

Restrict: Disallows the update or deletion of referenceddata.

Set to Default: When referenced data is updated ordeleted, all associated dependent data is set to a default

value.

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Referential integrity rules

Cascade: When referenced data isupdated, all associated dependent data iscorrespondingly updated. When a

referenced row is deleted, all associateddependent rows are deleted

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Data integrity constraints

Null Rule0A null is a rule defined on a single column that allows ordisallows inserts or updates of rows containing a null(the absence of a value) in that column.

Unique Column Values- A unique value defined on a column (or set of columns)

allows the insert or update of a row only if it contains aunique value in that column (or set of columns).

Primary Key Values-A primary key value defined on a key (a column or set of

columns) specifies that each row in the table can beuniquely identified by the values in the key.

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Other integrity constraints

Validation rules e.g.This integrity constraintenforces the rule that no row in this table cancontain a numeric value greater than 10,000 inthis column. If an INSERT or UPDATE

statement attempts to violate this integrityconstraint, then returns an error message.

CHECK Integrity Constraints

ACHECK

integrity constraint on a column or set ofcolumns requires that a specified condition betrue or unknown for every row of the table..Usually Boolean expression evaluated using thevalues in the row being inserted or updated.

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Levels of Abstraction in DBMS

Many views, single conceptual(logical)schemaand physical

schema.

Views describe how users

see the data-Filedescription,recorddescription

Conceptual schema defineslogical structure

Physical schemahowcomputer views data onsecondary device

Physical Schema

Conceptual Schema

View 1 View 2 View 3

Disk

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Summary

DBMS used to maintain, query large datasets. Benefits include recovery from system crashes,

concurrent access, quick applicationdevelopment, data integrity and security.

Levels of abstraction give data independence.

A DBMS typically has a layered architecture.

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Fundamental Concepts and Terminology

Data are facts. Some facts are more importantto than others. Some facts are importantenough to warrant keeping track of them in aformal, organized way.

Data" is a broad concept that can include thingssuch as pictures (binary images), programs, andrules. Informally, dataare the things you want tostore in a database

Data mining: applied to large volumes of data todiscover trends and patterns.

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Metadata

Meta means "about," so metadata is"about data," or, more specifically,"information about data." Metadata thatdescribes the fields and formats of

databases and data warehouses. Databasecontains fields such as Name, Address,City, and so on. Metadata names thesefields, describes the size of the fields, and

may put restrictions on what can go in thefield ( data schema) (for example,numbers only).

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Data Repository

A repository is a structure that stores andprotects data. (Database+metadata)

Repositories provide the following

functionality: add (insert) data to the repository

retrieve (find, select) data in the repository

delete data from the repository Some repositories allow data to be

changed, to be updated.

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Data Warehouse

Central repository of all data which anorganizations various business systems

collect.e.g. financial data used for

planning,marketing, contracting anddecision-making

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Data Repository

Repositories are like a bank vault. They existmainly to protect their contents from theft andaccidental destruction.

Security: repositories are typically passwordprotected, many have much more elaboratesecurity mechanisms.

Robustness: Accidental data loss is safeguardedagainst via the transactionmechanism.

A transactionis a sequence of databasemanipulation operations.

Data warehouse is the main repository of an

organization's historical data -management's

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Queries

Many DBMSs provide a user interface consistingof some sort of formal language.

A data definition language(DDL) is used to

specify which data will be stored in the databaseand how they are related. E.g. create table ordrop table

A data manipulation language(DML) is used

to add, retrieve, update, and delete data in theDBMS.

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Queries

A queryis often taken as a statement or groupof statements in either a DDL or a DML orboth. Some researchers view queries as read-

only operations, no data modifications areallowed e.g. Codd

A query languageis a formal language thatimplements a DDL, a DML, or both. Examples

of query languages include SQL (StructuredQuery Language),

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Database report

A database report presents informationretrieved from a table or query in apreformatted, attractive manner. Reporting

Services uses a SQL Server database forinternal storage. Microsoft Access can beused to create non-interactive HTML

reports. This is the easiest way to presentdatabase information on the Web.

D t M d l

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Data Models

A data modelis mathematical formalismconsisting of two

A notation for describing data, and

A set of operations used to manipulatethat data.

A data model is a way of organizing a

collection of facts pertaining to a systemunder investigation.

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Data models

Different models provide differentconceptualizations of the world; they havedifferent outlooks and different

perspectives. There is no universally agreed upon best

data model. The most common ones are

presented

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Overview of Database Design

Entity-Relationship Model

The ER model envisions the world ascomprised of entitiesthat are associated

with each other by relationships. All ofthe entities of a particular type arecollected together into entity sets. Anentity-relationship model (ERM) is anabstract conceptual representation ofstructured data;

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Overview of Database Design

What are the entitiesand relationshipsin theenterprise?

What information about these entities and

relationships should we store in the database? What are the integrity constraintsthat hold?

A database `schema?in the ER Model can berepresented pictorially (ER diagrams).

Can map an ER diagram into a relationalschema.

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Entities

Entities are distinguishable real-world objectssuch as employees, maps, airplanes, or busschedules.

-Distinguishable means that all entities can beuniquely identified.

-Entities have common attributes that definewhat it means to be such an entity.

-For any given real-world object, differentmodelers can choose different sets of attributesof the object that are of interest to their particularsituation.

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Relationship

A relationship Association among two or more entities.An association is a business component that defines arelationship between two entity objects based oncommon attributes. Relationship Set: Collection ofsimilar relationships.

Notation: two entity sets A and Bthat stand inrelationship r is written A rB.

Types of Relationship

One-One: if A rBand r is one-one then each entity of B

is in relationship with at most one entity of A and vice-versa. e.g. if CAPTAINcommands VESSEL andcommands is one-one then, in model, each vessel hasat most one captain and each captain commands atmost one vessel at a time.

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Types of Relationship

Many-one : if A rBand r is many-one then eachentity of A is in relationship with at most oneentity of Bbut not vice-versa. e.g. if CREWassigned-toVESSEL and assigned-to is

many-one then, in this model, a vessel hasmany crew members but a crew member isassigned to only one vessel.

Many-many if A r Band r is many-many then

each entity of A can be in relationship with anynumber of Bentities and vice-versa. if VESSELpatrols REGIONand patrols is many-manythen, in our model, a vessel patrols many

regions and a region is patrolled by many ships.

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ER model

isa -relationships: if A isa Bthen A is aspecialization of B, or, conversely, Bis ageneralization of A.

For example, if CAPTAINisa CREWthen,in model, captains have all the attributesof crew members but not vice versa.

The isa relationship allows hierarchies tobe established among entity sets.

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ER model basics

Consider Works: An employee can workin many departments; a dept can havemany employees.(one-many)

In contrast, each dept has at most onemanager, according to the key constrainton Manages.

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Primary and foreign key

Primary and Foreign key constraints are andwhat they are used for:

Primary Key:

A primary key is a field or combination of fieldsthat uniquely identify a record in a table, so thatan individual record can be located withoutconfusion.

Foreign Key: A foreign key (sometimes called a referencing

key) is a key used to link two tables together.Typically you take the primary key field from one

table and insert it into the other table where it

Primary and foreign key

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Primary and foreign keyconstraints

primary key constraint is a rule that says thatthe primary key fields cannot be null and cannotcontain duplicate data.

A foreign key constraint specifies that the datain a foreign key must match the data in theprimary key of the linked table.This system iscalled referential integrity, it is to ensure that

the data entered is correct and not orphaned(i.e. there are no broken links between data inthe tables)

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RDBMS

A relational database management systemisa DBMS based on the relational model asdefined by Codd.

There is no commercially available DBMS thatfully implements the relational model as definedby (Codd 1990). .

Advantages of the Relational Model

-queries can be automatically compiled,executed, and optimized without resorting toprogramming

-correctness: the semantics of the relational

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