Introduction to DBMS

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Introduction to DBMS

• Instructor Ebru SEZEResezer_at_ata.cs.hun.edu.tr

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• ENTITY SET Set of similiar objects
• Employees of companies is employee entitiy
  set
• ATTRIBUTE Description of entities
• For employee entity number, name, deptno,
  age, adr, salary..etc are attributes.
• RECORDStores whole information of an entity
• Fixed /variable length records
• Fixed/variable type records (Ex.
  ThesisLesson Stage Of BS)
• FILE Organization of whole datas of one entity
  set
• Employee file is keeps all employees
  record

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• Size of file
• Operation on Files
• Read
• Write
• Types Of Acces
• Sequential
• Random (Direct)
• KEY One or more field to used for retrieve or
  sort file
• Primary Key One or more field which van take
  unique value for an entity
• External Key Key which is composed aspects of
  physical storage of record

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Introduction to Information Sys

• Electronic form of data must be
• in collection
• organized
• stored
• They must be permanently
• Maintained
• Quickly updated and show changes
• Two main aspect of info sys.
• Capacity to management to perform necessary
  functions
• Availability of informations

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DATABASE

• Database Collection organization of related
  data
• Represents some aspects of real world called
  miniworld
• Logically coherent collection fo data. Random
  assortment of data con not reffered as db.
• Designed, builtin populated with data for
  specific purposes
• Table Basic logical unit for store data.
• Stores whole information of an entity set
• Defined by name and coloumns (attribute) set
• Can be altered after creation
• You can think that
• Info. of entity set is stored in files in
  physical structure , in tables in logical
  structure

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Sample Tables
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What Is a DBMS?

• A Database Management System (DBMS) is a software
  package designed to store and manage databases.
• With DBMS
• Supports large volumes
• Data independence and efficient access.
• Reduced application development time.
• Data integrity and security.
• Concurrent access, recovery from crashes.

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Structure of a DBMS
These layers must consider concurrency control
and recovery

• A typical DBMS has a layered architecture.
• The figure does not show the concurrency control
  and recovery components.
• This is one of several possible architectures
  each system has its own variations.

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Sample Database
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Levels of Abstraction

• Many views, single conceptual (logical) schema
  and physical schema.
• Views describe how users see the data.
  
• Conceptual schema defines logical structure
• Physical schema describes the files and indexes
  used.

View 1
View 2
View 3
Conceptual Schema
Physical Schema
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Exp University Database

• Conceptual schema
• Students(sid string, name string, login
  string,
• age integer, gpareal)
• Courses(cid string, cnamestring,
  creditsinteger)
• Enrolled(sidstring, cidstring, gradestring)
• Physical schema
• Relations stored as unordered files.
• Index on first column of Students.
• External Schema (View)
• Course_info(cidstring,enrollmentinteger)

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Data Independence

• Applications insulated from how data is
  structured and stored.
• Logical data independence Protection from
  changes in logical structure of data.
• Physical data independence Protection from
  changes in physical structure of data.

• One of the most important benefits of using a
  DBMS!

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People who deal with databases

• Database implimentors
• End users and DBMS vendors
• DB application programmers
• E.g. smart webmasters
• Database administrator (DBA)
• Designs logical /physical schemas
• Handles security and authorization
• Data availability, crash recovery
• Database tuning as needs evolve

Must understand how a DBMS works!
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Important Reason for looking inside db

• DBAs must know underlying technology to make
  decision
• (System installing, parameter setting)
• Decide best configuration of an application

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Database Languages(ext.)

• DDL define logical physical external schemas
• DMLquerying and updating db instances
• Host Languages C, C, Fortran..etc
• Tools
• Use interface of designers to form DML query
• Oracle designer, Power designer