04_05 modeling and design framework

8/7/2019 04_05 Modeling and Design Framework

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Session 04 and 05

Database SystemModeling and design Framework

TUE 23/11/2010


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K ey Terms cont.

Database System

A database, a database managementsystem and appropriate hardware andpersonnel.

number,Designation

Hoursworked, Pay

rateInsurance,

Pension


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Database System: Hardware

Set of physical devices on which a

database resides. It consists of oneor more computers, disk drives, CRTterminals, printers, tape drives,connecting cables and other auxiliary and connecting hardware.


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Database System: Hardware cont.

Client

Client

Server

TAPEPrinter


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Database System: Software

A database software includes two types of software General-purpose database management

software, usually called the databasemanagement system (DBMS)

Application software that uses DBMS

facilities to manipulate the database toachieve a specific business function, such asproviding reports or documents, which canbe used by users.


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Database System: Software cont.

Application software is generally writtenstandard programming language such as

C, or it may be written in a language(commonly called a fourth-generationlanguage) supplied with the DBMS.

These programs utilise the commandlanguage of the DBMS and make use of the information contained in the datadictionary.


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Database System: Software cont.

User Interface Language, menus and other facilities by

which users interact with various systemcomponents, such as application programs,the DBMS

Computer-aided software engineering(CASE) tools Automated tools used to design databases

and application programs.


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Data Dictionary/Directory(Repository)

A subsystem that keeps track of the definitions of all data items in the database.

relationships that exists between variousdata structures.

indexes that are used to access data quickly.

screen and report format definitions thatmay be used by various applicationprograms.


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Data DictionaryDefinitions of data items in the databaseincludes:

Elementary-level data items (fields),

group and record-level data structures, and

files or relational tables.


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Data that describe the properties orcharacteristics of data.Some of these properties include data definitions,data structures and rules or constraints. Itemname, the data type, length, minimum andmaximum allowable values (where appropriate)and a brief description of each data item.

Metadata allow database designers and users tounderstand what data exist, what the data mean.Data without clear meaning can be confusing,misinterpreted.

Metadata


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E.g.Data Item ValueName Type Length Min Max DescriptionName Character 30 Employee NameID Number 9 Employee No.Dept Character 10 Dept. No.Age Integer 2 18 60 Employee Age

Name Character 15 Dept. NameManager Number 9 Mgr. Emp. No.

Employee No. (ID) uniqueManager is an employee of the organisation

Metadata


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Database System: People

Two different types of people ( users andpractitioners ) are concerned with thedatabase.

Users who need information from the database to

carry out their primary businessresponsibility

e.g. Executives, managers, staff, clericalpersonnel


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Database System: People cont.

Practitioners

people responsible for the database

system and its associated applicationsoftware.

e.g. Database administrators, analysts,programmers, database and systemdesigners, information systems managers.


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Components of a Database System

Four components: People, H/W, S/W, Data

Practitioners (analysts and databasedesigners) in consultation with usersidentify data needs and design databasestructures to accommodate these needs.

The database structures are specified tothe DBMS through the data dictionary.


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Components of a DBS cont.

DATAB

ASE

DATADICTIONARY/DIRECTORY

ApplicationPro gram

ApplicationPro gram

ApplicationPro gram

DB MS

Computer Terminals

PRINTER

Analyst

User


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K ey Terms cont.Database Management System

Systems software that facilitates the

management of a database.E.g. Oracle, Access, SQL Server


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Database Management System(DB MS)

DBMS

An application software thatorganises data into records in oneor more databases and allowsorganising, accessing and sortingof the data in a variety of formats.


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DB MS cont.

Relational DBM S M ost common type of DBM S.

D ata elements are stored indifferent tables made up of rowsand columns. Relates data in

different tables through the useof common data element(s).


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Components of a DBMS

DATABASE

DATADICTIONARY/DIRECTORY

USER

PROGRA MM ER

Data Dictionary/Directory

SubsystemSecurity and

Inte gritySubsystem

Database AccessSubsystem

User Query and

Reportin g Facilities

ApplicationPro gram

Development

Facilities

DB MS

USER

PROGRA MM ER


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Data Security

The database is a valuable resourceneeding protection.

The DBMS provides database securityby limiting access to the database toauthorised personnel.

Authorised users will generally berestricted as to the particular data theycan access and whether they can updateit.


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Data Security

Access is often controlled by passwordsand by data views, which are definitionsof restricted portions of the database.

1

Data items

2 3 4


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Data Integrity

The integrity and consistency of thedatabase are protected via constraints onvalues that data items can have and bybackup and recovery capabilitiesprovided within the DBMS.

Data constraint definitions aremaintained in the data dictionary.


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Data Integrity

Backup and recovery are supported bysoftware that automatically logs changesto the database and provides for a meansof recovering the current state of thedatabase in case of system failure.


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Concurrent Data Access

One of the chief functions of the DBMSis to support the access, retrieval andupdate of data in the database.

The DBMS provides the physicalmechanisms allowing multiple users toaccess a variety of related data quicklyand efficiently.


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User-Oriented Data Manipulation

DBMS provides user-oriented datamanipulation tools.

Easy-to-use query languages allow usersto formulate queries and request one-time reports directly from the database.

Often query languages will containfacilities to format the results of queriesas reports.


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Data Manipulation

Report generators have more powerfulreporting facilities than those in thequery language.


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Application Development

The DBMS commonly providessignificant assistance to the applicationprogrammer. Tools for screen, menu and report

generation

application generators

compilers

data and view definition facilities


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Modern database systems providelanguage components that are muchmore powerful than those of traditionallanguages, making the programmingprocess itself considerably more efficient. Developer 2000/PowerBuilder for Oracle

Visual Basic for Microsoft SQL server


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Database ApplicationsD atabases range from those for a

single user with a desktop computer to those on mainframe computerswith thousands of users.

Personal databases

Workgroup databases

Departmental databases

Enterprise databases


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Personal Computer DatabasesD esigned to support one user with a

standard alone PC.

E.g. a sales person keeping track of this customer information withcontact details.


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Workgroup DatabasesA relatively small team of people (less

than 25) who collaborate on thesame project or application.

E.g. a software development teammaintaining a list of softwareobjects.


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Department DatabasesA department is a functional unit of an

organisation. It is larger than aworkgroup.

D epartment databases are designed tosupport the various functions andactivities of a department.

E.g. a personnel database that is designedto track data concerning employees, jobs,skills and job assignments.


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Enterprise DatabasesAn enterprise is one whose scope is

the entire organisation or enterprise.

Such databases are intended tosupport organisation-wideoperations and decision making.

E.g. a large health care organisation thatoperates a group of medical centre'sincluding hospitals, clinics and nursinghomes.


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Enterprise Databases cont.An enterprise database does support

information needs from manydepartments. The most importanttype of enterprise database today iscalled a data warehouse.

Data warehouse

An integrated decision support databasewhose content is derived from the variousoperational databases.


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Database Environment

Marketing Purchasing

Accounting

Marketin g

Sales Advertisin g

Accountin g

AccountsReceivable

AccountsPayable

Corporate Database


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3 Level ANSI/SPARC Architecture

ANSI SPARC is an acronym for the American National StandardInstitute Standard Plannin g and Requirements Committee.A standard three level approach to database desi gn has been a greed.

- External level- Conceptual level- Internal level (includes physical data stora ge)

The 3 Level Architecture has the aim of enablin g users to access thesame data but with a personalized view of it. The distancin g of theinternal level from the external level means that users do not need toknow how the data is physically stored in the database. This levelseparation also allows the Database Administrator (DBA) to chan gethe database stora ge structures without affectin g the users' views.

Made databases more independent of applicationBecame a standard for the or ganisation of DB MS


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3 LevelsExternal Users and Applications view of data

Conceptual Logical Data Model

Physical Physical data Model


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External (Sub) Schema defines the external view of data

as seen by a user or program

Conceptual Schema defines the logical view of dataas seen by all users and programs

Physical (Internal) Schema defines the physical view of data

as seen by a DBMS


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user a user i /program j program x

sub-schema a sub-schema i sub-schema z

conceptual schema

physical schema

3 Level Architecture

Databases


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Name (20 characters) Address (40 characters)

NID (10 char) Designation (15 char)

Physical View

database

A.B.C. Rudra Prasad | 222 , Gole Road, Pune |

65 037 069 0V | Lecturer

The DBMS must know exact physical location precise physical structure

Employee record


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Physical ViewPhysical view provides the disk drives,physical addresses, indexes and pointers.Physical Database Design is theresponsibility of the DatabaseAdministrator (DBA). No user is concernedwith this view.

Physical devices to contain the dataAccess methods to retrieve and update datamaintain and improve database performance


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database

Logical View

Address 222 , Galle Road, Colombo

The user/application mustknow

existence logical reference Employee

Name A.B.C. De Silva

Designation Senior Lecturer

NID 65 037 069 0V


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Logical ViewThis is a single logical description of alldata elements and their relationships.It is the result of the conceptual designwhich involves analysis of all usersinformation needs and data definitionof data items needs to meet them.

SQL CREATE TABLE statement isused to define the data elements.


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database

External View

Department Dept. of Computer Science

The user/application see authorised data

own formatLecturer

Name A.B.C. De Silva

Designation Senior Lecturer Age 35


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External View

This consists of user views of thedatabase.

Each definable user group will have itsown view of the database.Each of these views gives a user-

oriented description of the dataelements and relationships of which theview is composed.


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A logical description of some portion of the database that is required by a userto perform some task.

E.g. Benefit application user will viewpart of the employee data, excludingdata such as date of birth and salary.

User View


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External View

It can be derived directly from theconceptual schema.

The collection of all user views is theexternal level.SQL CREATE VIEW statement is used

to create these views and SQL GRANTstatement is used to restrict its use to auser group.


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External Views Allows to hide unauthorised data

e.g. s alary, dob

provide user viewe.g. view employee n ame, de s ig n atio n ,departme n t data taken from employee and

departmen

t files derive new attributes

e.g. age derived from dob or n id

External View cont.


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External Views Allows to change unit of measurement

e.g. show age in years or months define security levels

e.g. update access to employee fileread-only to departme n t file

External View cont.


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Mapping between Levels

DBMS map or translate from one levelto another.

External ConceptualConceptual Physical

Database exists in reality only at theinternal level.


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user a user i /program j program x

sub-schema a sub-schema i sub-schema z

conceptual schema

physical schema

Databases

DDL

SDDL

DML/SQL

Practitioners:DBA

Users


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Data Definition Language (DDL)- is the language component of a DBMS

that defines each data element as itappears in the database.

Sub-Schema Data Definition Language(SDDL)

- is the language component of a DBMSthat defines data elements as it shouldappear to the end users andprogrammers.

Practitioners:DBA


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Data Manipulation Language (DML)- is a language associated with a DBMS

that is employed by end users and

programmers to manipulate data in thedatabase.

Structured Query Language (SQL)

- pronounced as sequel, is the standarddata manipulation for relational DBMSs.

User


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Characteristics of Early DBMS

Centralised Storage ManagementTransaction ManagementRecovery FacilitiesSystem Maintained Access Paths


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Characteristics of Modern DBMSQuery processing and optimisationTransaction management

Concurrency controlDatabase recoveryDatabase security and authorisation

Distributed databasesData warehousing and data mining


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Function of a DBMSFunctions of a DBMS are concerned with

providing efficient flexible dataprocessing capabilities withoutcompromising data validity.

Main Functions are: Shared data

Control redundancy Data integrity Data security


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Capabilities of a DBMS

Capabilities vary considerable, but basicoperations are:Data definitionData entryData manipulationData display


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AdvantagesProgram-data independenceMinimal data redundancyImproved data consistencyImproved data sharingIncreased productivity of applicationdevelopmentEnforcement of standardsImproved data qualityImproved data accessibility and responsivenessReduced program maintenance

Database Approach


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The separation of data descriptions(metadata) from the application programsthat use the data.

In the database approach data descriptionsare stored in a central location called thedata dictionary. This property allows anorganisations data to change and evolve(within limits) without changing theapplication program that process the data.

Program-Data/Data Independence


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Data files are integrated into a single,logical structure. Each primary fact isrecorded (ideally) in only one place in thedatabase.

E.g. Employee data not with the payroll andbenefit files.

Note: Data redundancy is not eliminated

entirely. Some data items will appear inmore than one place (e.g. employee no.) torepresent the relationship with others.

Minimal Data Redundancy


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By eliminating (or controlling) dataredundancy, we greatly reduce theopportunities for inconsistency.

E.g. employee address is stored only onceand hence we cannot have disagreementon the stored values.Also, updating data values is greatlysimplified and have avoid the wastedstorage space.

Improved Data Consistency


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A database is designed as a sharedcorporate resource. Authorised usersare granted permission to use the

database, and each user (or group of users) is provided one or more userviews to facilitate this use.

E.g. employee data common to payroll,benefit applications will be sharedamong different users.

Improved Data Sharing


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A major advantage of the databaseapproach is that it greatly reduces thecost and time for developing new

business applications. Programmer could concentrate on the

specific functions required for the newapplication, without having to worry aboutdesign or low-level implementation details;as related data have already been designedand implemented.

Increased Productivity of



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DBMS provides a number of high-levelproductivity tools such as forms and reportgenerations and high-level languages that

automate some of the activities of databasedesign and implementation.

Increased Productivity of

Application Development cont.


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When the database approach is implementedwith full management support, the databaseadministration function should be grantedsingle-point authority and responsibility forestablishing and enforcing data standards.

Standards include naming conventions, dataquality standards and uniform procedures foraccessing, updating and protecting data.

Powerful set of tools for developing andenforcing these standards are available for someDBMS.

Enforcement of Standards


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A number of tools and processes are available toimprove data quality. Database designers can specify integrity

constraints that are enforced by the DBMS. One of the objectives of a data warehouse

environment is to clean up operational databefore they are placed in the data warehouse.

ConstraintA rule that cannot be violated by database users.

Improved Data Quality


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With relational database, end users withoutprogramming experience can often retrieve anddisplay data, even when it crosses traditionaldepartmental boundaries.

English-like query language SQL and query toolssuch as Query-By-Example provide suchfacilities.

Improved Data Accessibilityand Responsiveness


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Stored data are changed frequently forvariety of reasons such as new data itemstypes are added, and data formats change(e.g. date format from two-digit to fourdigit).

Data independence allows to reduce theprogram maintenance time.

Reduced ProgramMaintenance


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DisadvantagesDBMS are more vulnerable than file-basedsystem because of the centralised nature of

a large integrated database.If a failure occurs the recovery process ismore complex and some times may resultsin lost transactions.Hardware, software and personnel cost arehigher for DBMS.

Database Approach

04_05 modeling and design framework

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