Lesson I Database Management Systems - XTEC · DBMS DBMS vs File-based Systems ... DBMS Elements A...

Lesson I

DatabaseManagement Systems

2

IN THIS LESSON YOU WILL LEARN…

� The concept and importance of information .

� What an information system is and its components.

� The structure of data files and the drawbacks of file-based system .

� What a database is and the advantages of using a database management system .

� The meaning of data model and a list of the main data models in use.

� The three layer architecture for databases.

� The different users of a database.

1. Information

2. Information Systems

3. File-based IS

4. Database Management Systems (DBMS)

5. Data Modelling

6. ANSI/SPARK Architecture

Information

1. INFORMATION1.1 Introduction

1.2 Importance

1.3 Information vs Computer Science

1.4 Quality of Information

1.5 Properties of Information

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INFORMATIONIntroduction

� Nowadays, the amount of information we areexposed to is huge.

e.g: weather prediction, horoscopes, traintimetable...

� All areas of human development need to manipulate information.

� This information is changing constantly.

Why isinformationso important?

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INFORMATIONImportance

� In our society the information has become a very important resource.

� In addition, all organisations need to saveand access data.

Relevant and timely information is essential to make decisions .

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INFORMATIONInformation vs Computer Science

� In Catalan and Spanish the term computerscience comes from the French word:

informatiqueinformation automatique

That is what we are interested in!!

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INFORMATIONInformation vs Data

� Data are the record of facts. It can be only series of numbers or characters with no meaning.

� Information implies that the data have beenprocessed so that they mean something for the recipient.

Activity 1.1Information vs Data

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INFORMATIONQuality of Information

� Information is considered high-quality if itpermits the recipient to make the best decision.

� The quality of the information is moreimportant than its quantity.

� There are a set of properties that allow you to assess the quality of the information.

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INFORMATIONProperties of Information

- reported in time

- understandable

- up to date

- reliable to the user

- safe

- relevant

- accurate

- complete

- transmitted to theright person

It’s not possible to get all of them!!

Activity 1.2Quality ofInformation

1. Information


3. File-based IS


5. Data Modelling


InformationSystems

2. INFORMATION SYSTEMS2.1 Concept

2.2 Components

2.3 Connection between Components and Objectives

2.4 Analysis and Design

2.5 Automated Information Systems

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INFORMATION SYSTEMSConcept

� Companies and organisations have an infrastructure that allows the information to be manipulated quickly and easily.

Organisation’sINFORMATION SYSTEM (IS)

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INFORMATION SYSTEMSComponents

� An information system is made up of:

– information– users– physical support– working procedures

Can you guess what each of these components is?

Who decides on the information system?

2. INFORMATION SYSTEMS2.1 …

2.2 Components– Information

– Users

– Physical Suport

– Working Procedures

2.3 …

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INFORMATION SYSTEMSInformation

� It’s the most important component of the systems.

Which information must be stored?



– Users

– Physical Suport


2.3 …

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INFORMATION SYSTEMSUsers

� People that insert, manipulate or use the information to carry out their tasks.

Who is manipulating

the information?



– Users

– Physical Suport


2.3 …

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INFORMATION SYSTEMSPhysical Support

� All devices used to communicate, process and store information.

Which physical elements will be used to manipulate the

information?

Are computerspart of thephysicalsupports in allIS?

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� It’s possible to find information systems that only use basic tools to manipulate information.

� Nowadays computers have replaced those old tools.

Although they are not essential!!

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INFORMATION SYSTEMPhysical Support

data file

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INFORMATION SYSTEMPhysical Support

� We are interested in IS that do use computers to manipulate information.

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The databasesystems are theheart of all currentIS because theyallow to managelarge amounts of data.



– Users

– Physical Suport


2.3 …

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INFORMATION SYSTEMSWorking Procedures

� The IS must help to achieve the general objectives of the company.

� So, the managers decide a set of workingguidelines that they consider more efficientand useful.

How should things be done?

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INFORMATION SYSTEMSConnection between Componentsand Objectives

� The working procedures determine the:

– necessary information

– involved users

– necessary physical support

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INFORMATION SYSTEMSConnection between Componentsand Objectives

� The working procedures also have to adapt to the available elements:

– information

– characteristics of the users

– existing technology

What is the role of a databaseexpert in a non-automated IS?

Activity 1.3

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INFORMATION SYSTEMS

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INFORMATION SYSTEMSAnalysis and Design

databases

application programs

information system

Activity 1.4Identifying the components of an IS

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INFORMATION SYSTEMSAutomated Infomation Systems

� An automated IS is made up of the followingelements:

– information

– working procedures

– users

– software

– hardware

– administrator

Is it the only physical support used?

1. Information


3. File-based IS


5. Data Modelling


File-basedInformationSystems

3. FILE-BASED IS’s3.1 Files

3.2 Concept

3.3 Separate Application Programs

3.4 Drawbacks

3.5 Database

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FILE-BASED INFORMATION SYSTEMSFiles

� The computer’s RAM memory is volatile.

� The file is a high-level structure provided by the operating system that keeps the data in mass storage.

� Different types of files store different types of information.

� We are interested in data files and database files.

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FILE-BASED INFORMATION SYSTEMSConcept

� Data files are used to store the information.

� In the same company or organisation, thereare several programs that perform servicesfor the final users.

� Each program defines and manages its owndata.

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FILE-BASED INFORMATION SYSTEMSSeparate Application Programs

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SEPARATE PROGRAMSExample

� Consider two departments in our college:

-admissions office-personnel

� Both of them need to keep information about the teachers but the information required is slightly different.

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SEPARATE PROGRAMSExample

This approach has several limitations!!

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FILE-BASED INFORMATION SYSTEMSDrawbacks

- Data dependence

- Incompatible file formats

- Security problems

- Data redundancy …

What are these disadvantages about?

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FILE-BASEDIS DRAWBACKSData Dependence

� If some modifications have to be made in thedata, then the application program has to be rewritten.

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FILE-BASEDIS DRAWBACKSIncompatible File Formats

� The structure of the file depends on theapplication programming language.

e.g. the structure of the files generated by C and Visual Basic may be different.

o The incompatibility of such files makes it difficult to process them together.

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FILE-BASEDIS DRAWBACKSSecurity Problems

� There are no mechanisms to control thedifferent permissions on the users.

� In case of a system crash it also becomeshard to recover the data to a consistent state.

3. FILE-BASED IS’s…

3.4 Drawbacks– Data Dependence

– Incompatible File Formats

– Security Problems

– Data Redundancy

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FILE-BASEDINFORMATION SYSTEMSData Redundancy

� Data redundancy means duplication of data.

� Data redundancy leads to:

-wastage of storage space

-more laborious updating process

- loss of data integrity!!

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LOSS OF DATA INTEGRITYExample

� Let’s imagine that one of the teachers moves to another address:

BUT..

Files with contradictory information!!

What of thepreviousdisadvantages isthe worst?

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To solve theproblems mentionedbefore...

databasesystems

A database is a well-organised collection of data that is related in a meaningful way.

How do databasesystems solvethe problemsmentioned?

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DATABASEDefinition

� All the data needed by the organisation are in the database.

� All users access a single place to get theinformation they need.

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DATABASEIntegrated Information

1. Information


3. File-based IS


5. Data Modelling


DatabaseManagement Systems

4. DBMS4.1 Concept4.2 Data Access4.3 Advantages4.4 DBMS vs File-based

Systems4.5 Drawbacks4.6 Elements4.7 Languages4.8 Users

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DATABASE MANAGEMENT SYSTEMConcept

� A DBMS is a collection of programs thatpermits the user to create and manipulatedatabases.

� The DBMS provides the interface betweenthe database and the programs that accessthe data.

Do you know any DBMS?e.g: Access, MySQL, Oracle, Postgress, ...

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DBMSData Access

What are theadvantages ofhaving all thedata in a single place?

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DBMSAdvantages

- Data dependence

- Incompatible file formats

- Security problems

- Data redundancy

- Data independence

- Data standardization

- Security tools

- Controlled redundancy

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ADVANTAGES DBMSData Independence

� Data independence means independencebetween application program and data.

� When the data representation changes, it is not necessary to change the applicationprogram.

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ADVANTAGES DBMS Data Standardisation

� There’s a greater degree of data standardization within the organisation.

� The users are obliged to use the same data definitions.

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ADVANTAGES DBMSControlled Redundancy

� Since the data are recorded only once:

– data need less space

– the data updating process is easier

– there’s no data inconsistency!!

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ADVANTAGES DBMSSecurity Utilities

� Access to data can be restricted so that only authorised users may see or manipulate it.

� Backup copies of data need to be made regularly to recover in case of system failure.

4. DBMS…4.3 Advantages

– Data Independence– Data Standardisation– Controlled Redundancy– Security Utillities

4.4 DBMS vs File-based Systems

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DBMSDBMS vs File-based Systems

FILE-BASED SYSTEM DBMS SYSTEM

Data dependence Data independence

Incompatible file formats Data standardization

Data redundancy Controlled redundancy

Security problems Backup and recovery utilitiesRestricted authorized access

Activity 1.5Advantagesof a DBMS

Is there anydisadvantage ofusing a DBMS?

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DBMSDisadvantages

� The enterprise may be assuming additional risks in the following areas:

– the cost of using DBMS

– data integrity

– data quality

– confidentiality, privacy and security

– enterprise vulnerability

Activity 1.6Disadvantagesof a DBMS

What can you do with a DBMS?

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DBMSElements

� A practical database package tipicallyprovides utilities for:

- Design and maintenance of database structures

- Formulation of queries- Design of forms- Design of reports- Contruction of macros and

programs

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DBMSLanguages

� The DBMS has languages and procedures to communicate with the database.

– Data Definition Language (DDL)

– Data Manipulation Language (DML)

What is the purpose of these languages?

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DBMS LANGUAGESData Definition Language

� It operates on the data structures.

� It is used to:

- define a database

- modify its structure

- destroy it when you no longer need it

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DBMS LANGUAGESData Manipulation Language

� It operates on the data.

� There are four things that you can do with data:

– store the data– change the stored data– remove data from the database– retrieve data from a database

Activity 1.7DBMS Languages

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DBMSUsers

� A database involves a group of people:

– database designer

– database users

– database administrator

What are these people in charge of?

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USERS OF A DBMSDatabase Designer

� The database designer is responsible for:

– Identifying the data to be stored in thedatabase.

– Choosing an appropriate structure to represent and store the data.

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USERS OF A DBMSDatabase Administrator

� The objectives of DBA are:

- To control the access to the database

- To restore a consistent state of the databasefrom a system failure

- To standardize the use of databases

- To support the development and maintenanceof database application programs

- To ensure all the documentation is up-to-date

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USERS OF A DBMSDatabase Users

� They are people who need information from thedatabase to carry out their tasks.

Application programmers:

Write application programs and interact with the database through a host language like Pascal or C

End users

- Specialized end users- Non-experienced final users

Database users

1. Information


3. File-based IS


5. Data Modelling


Data Modelling

5. DATA MODELLING5.1 Concept of Modelling5.2 Why Modelling?5.3 Meaning of Data

Modelling5.4 Advantages5.5 Difficulties

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MODELLINGConcept

� A model of something is a representation thatshares certain relevant features with theoriginal.

e.g. An actual physical scale modelA musical score

A plan of a house

A set of equations

Can you give examples of models?

Why modelling?

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MODELLINGWhy Modelling?

� Models are useful because the characteristicsof the real system can be analysed bystudying the nature and behaviour of themodel.

� Models can give an accurate description.

There’s no ambiguity!!

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DATA MODELLINGMeaning

� We need techniques that allow us to representa conceptual view of the informationinvolved in information systems.

� Data models are also concerned about theprocessing of data and the definition of operations on these.

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DATA MODELLINGMeaning

The real system to be modelled usually refers to a company or organisation.

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DATA MODELLINGAdvantages

� The use of data models provides a betterunderstanding of the nature of information.

� They enable a better design of databasesystems.

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DATA MODELLINGDifificulties

� One difficulty in data modelling is thedifference between the human view of an IS and the way it has to be implemented withinthe computer.

� To solve this, we can view the architecture of a database as a series of levels that providedifferent degrees of abstraction.

1. Information


3. File-based IS


5. Data Modelling


ANSI/SPARK Architecture

6. ANSI/SPARK ARCHITECTURE6.1 Concept6.2 Levels of Abstraction6.3 Logical Level6.4 Pysical Level6.5 Schemas6.6 Types of Data Models6.7 Data Independence

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ANSI/SPARC DATA MODELConcept

� Proposed by ANSI/SPARC for databasesystems.

� The data in a DBMS is represented at threelevels of abstraction.

� There’s a schema at each of these levels.

� A schema is the structure of the database, described in a formal language supported by the DBMS.

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ANSI/SPARC DATA MODELLevels of Abstraction

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ANSI/SPARK DATA MODEL

To do this we need...

DATA MODELS

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DATA MODELSTypes

� There is a large number of data models:

– Hierarchical Model

– Network Model

– Relational Model

– Entity-Relationship Model

– Object-Oriented model

– ...

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ANSI/SPARC DATA MODELLevels of Abstraction

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ANSI/SPARC DATA MODELLogical Level

� The “reality” of the information system is represented to obtain a conceptual schema .

� From this schema, it’s described what data arestored.

� The logical schema contains the organisationof the data into tables and columns.

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ANSI/SPARC DATA MODEL

ER model

Relational model

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ANSI/SPARK DATA MODELPhysical Level

� It describes how the data relations described in the conceptual schema will be physically storedusing a particular DBMS.

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ANSI/SPARC DATA MODELExternal Level

� It is the highest level of abstraction.

� An external schema is the view that theindividual user of the database has.

Users are not allowed to access all theinformation in the database

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LOGICAL LEVELConceptual Schema

� The real-world information system is represented to obtain a conceptual schema .

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CONCEPTUAL SCHEMAExample

Entity-relationship diagram

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LOGICAL LEVELLogical Schema

� From this schema, it’s described what data arestored.

� The logical schema contains the organisationof the data into rows and columns.

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LOGICAL SCHEMAExample

TEACHER (id, name, address )

SUBJECTS (code, name, hours, id_teacher)

foreign key: id_teacher �TEACHERS

Relational Model

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LOGICAL SCHEMAExample

TEACHER (id, name, address )

SUBJECTS (code, name, hours, id_teacher)

foreign key: id_teacher �TEACHERS

id name address

12 Fox BCN

25 McKewan BCN

80 Fox GRN

code name hours id_teacher

C1 OS 240 25

C2 NET 180 25

C3 DB 60 12

TEACHERS SUBJECTS

tables

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DATA MODELSTypes

SCHEMA MODEL

Conceptual Schema (real-world)

Entity-Relationshipmodel (ERM)

Logical Schema (data description)

-Relational model-Hierarchical model-Network model

Internal Schema(implementation of tables) �

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DATA MODELSHierarchical Model

� Formed the basis of the earliest databases.

� Organised data were arranged on a top-downstructure.

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DATA MODELSNetwork Model

� It was a more general representation of thehierachical model with no distiction betweenparent and child.

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DATA INDEPENDENCE

� Data independence means that the changes in the way the data are structured and storeddon’t affect the programs.

– Physical data independece

– Logical data independence

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DATA INDEPENDENCEPhysical Data Independence

� It is the ability to modify physical schemawithout causing the conceptual schema or application programs to be rewritten.

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DATA INDEPENDENCEPhysical Independence

PHYSICAL INDEPENDENCE

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DATA INDEPENDENCELogical Data Independence

� It’s the ability to modify the conceptual schemawithout having to change the externalschemas or application programs.

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DATA INDEPENDENCEPhysical vs Logical Data Independence

LOGICAL INDEPENDENCE

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DATA INDEPENDENCEPhysical vs Logical Data Independence

PHYSICAL INDEPENDENCE

LOGICAL INDEPENDENCE

Lesson I Database Management Systems - XTEC · DBMS DBMS vs File-based Systems ... DBMS Elements A...

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