Data Base Organization and File Structure Chapter 1

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Data Base Organization and File Structure
Chapter 1

• Suresh Choubey, Ph.D.

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Chapter 1 Introduction

• What is a data database?
• A database is a collection of very large
  integrated collection of related data
• Data are facts about people, event and other
  entities that can be recorded and that have
  implicit meaning, e.g., name, address and
  telephone of all people we know

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Chapter 1 Introduction

• Characteristics of a database?
• A database is logically coherent collection of
  data with some inherent meaning
• A database is designed, built and populated with
  data for a specific purpose
• A database represents some aspect of real world,
  called mini world (models real world enterprise)
• Entities, relationship

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Chapter 1 Introduction

• What is a database management system?
• Database management systems (DBMS) is a
  collection of programs that enables users to
  create (store) and maintain a database. It
  involves design, construction (storage of data)
  and manipulation
• Database systems DBMS database

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Chapter 1 Introduction

• Characteristics of database approach
• Self-contained nature of database systems
• Data meta data constraints on data are stored
  together in system catalog
• Application programs are independent of data
• Insulation between programs and data
• DBMS access programs are independent of files
• This property is called program-data independence

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Chapter 1 Introduction

• Characteristics of database approach(Cont. .)
• Data abstractionDBMS gives conceptual
  representation of data, e.g. data model
• Support of multiple views of data
• Different users have differing views of database
• Virtual data can be derived

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Chapter 1 Introduction

• Intended use of DBMS approach
• Controlled redundancy
• Redundancy causes duplication of efforts, wastage
  of storage space and inconsistency
• Controlled redundancy may be useful in saving
  access time as some controlled data are stored at
  more than one place
• Sharing of data
• Requires concurrency control measures

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Chapter 1 Introduction

• Intended use of DBMS approach (Cont. .)
• Restricting unauthorized access
• DBMS provides security and authorization
  subsystems
• Providing multiple interfaces
• Query language for casual users, programming
  language for application programmers, forms for
  pragmatic users, menu driven interfaces for
  native users and natural language interfaces

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Chapter 1 Introduction

• Intended use of DBMS approach (Cont. .)
• Representing complex relationships among data
• Enforcing Integrity constraints
• Providing backup and Recovery from crashes
• Potential for enforcing standards
• Flexibility can add changes in mini world
• Reduced application development time

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Chapter 1 Introduction

• Intended use of DBMS approach (Cont. .)
• Availability of up-to-date information
• Economics of scale
• Permits consolidation of data and application
• Uniform data administration

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Chapter 1 Introduction

• Disadvantages of DBMS approach
• High cost due to high initial investment for h/w
  and s/w and incorporation of sub-systems for
  security, concurrency control, recovery and
  integrity function
• Security Problems
• Initial development time

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Chapter 1 Introduction

• File Vs databases (Slide from text book author)
• Application must stage large datasets between
  main memory and secondary storage (e.g.,
  buffering, page-oriented access, 32-bit
  addressing, etc.)
• Special code for different queries
• Must protect data from inconsistency due to
  multiple concurrent users
• Crash recovery
• Security and access control

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Chapter 1 Introduction

• Why study databases ? (Slide from text book
  author)
• Shift from computation to information
• at the low end scramble to webspace (a mess!)
• at the high end scientific applications
• Datasets increasing in diversity and volume
• Digital libraries, interactive video, Human
  Genome project, EOS project
• ... need for DBMS exploding

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Chapter 1 Introduction

• Why study databases ? (Slide from text book
  author)
• DBMS encompasses most of CS
• OS, languages, theory, AI, multimedia, logic

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Chapter 1 Introduction

• Personnel
• DBA responsible for database and DBMS, account
  allocation, security maintenance
• Database designers
• Identify data and design data structures
• Identify views and combine them
• DBMS designers and implementers

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Chapter 1 Introduction

• Personnel (Cont. .)
• End users access database for querying,
  updating and generating reports
• Casual end users
• Naïve or parametric end users use canned
  transactions
• Sophisticated end users
• Tool developers
• Operators and maintenance personnel

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Chapter 1 Introduction

• DBMS can be network, relational, hierarchical and
  others
• DBMS can also be single-user or multi-user
• DBMS can be centralized or distributed (DDBMS)
• homogeneous(use same DBMS s/w at multiple sites)
• Heterogeneous (use s/w to access several
  autonomous pre-existing database)

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Chapter 1 Introduction

• Data Models
• Is a set of concepts that describes the structure
  of the database (i.e., data types, relationship
  and constraints that should hold on data)
• Is a set of operators for specifying retrievals
  and updates on database
• Provides abstraction

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Chapter 1 Data Models

• A schema is a description of a particular
  collection of data, using the a given data model
• The relational model of data is the most widely
  used model today
• Main concept relation, basically a table with
  rows and columns
• Every relation has a schema, which describes the
  columns, or fields

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Chapter 1 Data Models Cocepts

• High level called object based models
• Entity - is an object hat is represented in the
  database
• Attribute is a property that describes some
  aspects of object
• Relationship
• Implementation Level record-based data models
  such as relational and network
• Physical data models describes how data is
  stored in the computer by representing
  information such as record formats, record
  orderings and access path

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Chapter 1 Data Models

• Database SchemasIs the description of database.
  Schema diagrams are used to represent it. Schema
  diagram consists of schema construct. e.g.,
  Student

• It does not change frequently
• Called INTENSION
• Database Instance Data in database at a
  particular time or occurrence or state
• called EXTENSION

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Chapter 1 DBMS Architecture (Three schema or
ANSI-SPARC)
External view - 1
External level or view level
External View - n
External/Conceptual mapping
Conceptual Schema
Conceptual level
Conceptual/Internal mapping
Internal Schema
Internal level
Stored database
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Chapter 1 Data Models

• Many views, single conceptual (logical) schema
  and physical schema
• External View contains n view, each view schema
  describing view of one user
• Conceptual View describes structure of whole
  database for a community of users
• Internal View describes physical storage
  structure of database
• Provides abstraction

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Chapter 1 Data Models

• Mapping required to map users request to
  conceptual to internal to stored database and
  then back after formatting it to suit the users
  view of database
• Data Independence Capacity to change the
  conceptual schema without having to change
  external schema or application programs
• Applications insulated from how data is
  structured and stored

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Chapter 1 Data Models

• Logical Data Independence Protection from
  changes in logical structure of data
• Physical Data Independence Protection from
  changes in physical structure of data

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Chapter 1 Data Models

• Physical Data Independence Physical data
  independence capacity to change the internal
  schema without having to change the conceptual
  (or external) schema
• Change to reorganize physical files by creating
  additional access structures
• Mapping information is stored in catalog
• Disadvantages Overhead when compiling or
  executing a query or program ? inefficiency in
  DBMS

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Chapter 1 Data Models

• Example 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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Chapter 1 DBMS Languages

• DDL can be used to define conceptual and
  internal schema in DBMS, where there is no strict
  separation
• DDL is used to specify conceptual and SDL to
  specify internal where there is separation
• VDL is used to specify user views and their
  mapping to conceptual
• VDL statements can be compiled separately or can
  be imbedded in a programming language

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Chapter 1 DBMS Languages

• DML is used for retrieval, insertion, deletion
  and modification of data
• High level or non-procedural DML
• Can be used to specify complex database operation
• Called set-at-a-time or set oriented DML
• Low level or procedural DML
• Embedded in a general-purpose programming
  language
• Called record-at-a-time DML

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Chapter 1 DBMS Languages

• DML is declarative as it set what to retrieve
  and not how to retrieve
• When DML is embedded in a programming language
• DML is called data sub-language
• Programming language is called host language
• DML standalone is called Query Language

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DBMS architecture (Slide from text book author)
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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Chapter 1 Summary (Slide from text book author)

• DBMS used to maintain, query large datasets.
• Benefits include recovery from system crashes,
  concurrent access, quick application development,
  data integrity and security
• Levels of abstraction give data independence
• A DBMS typically has a layered architecture
• DBAs hold responsible jobs and are well-paid
• DBMS RD is one of the broadest, most exciting
  areas in CS