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04/07/23 Rajesh.... 1
Database Basics by Database Basics by Rajesh………………..Rajesh………………..
Faculty,Faculty,MCA Course, B.R.A.BIHAR UNIVERSITY, MCA Course, B.R.A.BIHAR UNIVERSITY,
MUZAFFARPUR, BIHARMUZAFFARPUR, BIHAR
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Database and Information Systems• An information system is a well-coordinated collection
of resources that gather and transform data into information products and services that help the enterprise perform its designed functions.– retrieves, updates and deletes these facts– derives other facts from existing ones
• Data - raw facts/details of the model
• DATABASE- A shared collection of logically related data (and a description of this data), designed to meet the organisation needs of an organisation
• The Database Management System (DBMS) - software that enables users to define, create and maintain the database and provides controlled access to the database
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Introducing the Database• Data versus Information
– Data constitute building blocks of information
– Information produced by processing data– Information reveals meaning of data– Good, timely, relevant information key to
decision making– Good decision making key to
organizational survival
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Database• A database is a logically coherent
collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.
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DBMS• It is a collection of programs that
enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
What is a Database system?The database and DBMS software together is called as Database system.
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Functions of a DBMS Data storage, retrieval, update
A user-accessible catalog
Transaction support
Concurrency control
Recovery services
Authorisation services
Support for data communication
Integrity services
Data independence
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Interaction of DBMS with Operating System
DISK MANAGER
DatabasePhysical record
occurrences
DBMS
FILE MANAGER
request for stored record
request for stored page
disk I/O operation
returned stored record
returned stored page
retrieved data
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Data Models, Schemas and Instances
Specifies the allowable logical structures and operations in a database. A DBMS operates always according to a specific data model eg relational
The description of a database for a particular universe of discourse which follows the rules layered down by the data model supported by the target DBMS
The data in the database at a particular moment in time
Data Model
Database Schema (intension)
Database Instance (extension)
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Advantages of DBMS• Sharing of data• Enforcement of security• Enforcement of development and maintenance
standards• Reduction of redundancy• Avoidance of inconsistency across files• Maintenance of integrity• Data independence
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Disadvantages of DBMS
• size• complexity• cost• Additional hardware costs• Higher impact of failure• Recovery more difficult
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Maintaining a Database System - the Task of the DBA
• Maintaining information structure of the database (metadata in the Data Dictionary)
• Define user requirements of data usage• Monitor use of database• Determine and optimise storage structure and
access strategies• Define authorisation checks• Define strategies for backup and recovery• Define testing procedures and changeover
policy
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Classification of DBMS1. Classical DBMS
• Hierarchical
• Network
• Relational
2. New Directions
• Extended Relational
• Object-Oriented
• Distributed
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Database Models• Collection of logical constructs used
to represent data structure and relationships within the database– Conceptual models: logical nature of
data representation– Implementation models: emphasis on
how the data are represented in the database
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• Relationships in Conceptual Models– One-to-one (1:1)– One-to-many (1:M)– Many-to-many (M:N)
• Implementation Database Models– Hierarchical – Network – Relational
Database Models (con’t.)
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Hierarchical Database Model
• Logically represented by an upside down tree– Each parent can have many children– Each child has only one parent
Figure 1.8
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Hierarchical Database Model
• Advantages– Conceptual simplicity– Database security and integrity– Data independence– Efficiency
• Disadvantages– Complex implementation– Difficult to manage and lack of standards– Lacks structural independence– Applications programming and use complexity– Implementation limitations
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Network Database Model• Each record can have multiple parents
– Composed of sets– Each set has owner record and member record– Member may have several owners
Figure 1.10
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Network Database Model• Advantages
– Conceptual simplicity– Handles more relationship types– Data access flexibility– Promotes database integrity– Data independence– Conformance to standards
• Disadvantages– System complexity– Lack of structural independence
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Relational Database Model• Perceived by user as a collection of
tables for data storage• Tables are a series of row/column
intersections• Tables related by sharing common
entity characteristic(s)
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Relational Database Model (con’t.)
Figure 1.11
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Relational Database Model• Advantages
– Structural independence– Improved conceptual simplicity– Easier database design, implementation,
management, and use – Ad hoc query capability with SQL– Powerful database management system
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Relational Database Model
• Disadvantages– Substantial hardware and system
software overhead– Poor design and implementation is
made easy– May promote “islands of
information” problems
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Object-Oriented Database Model
• Objects or abstractions of real-world entities are stored – Attributes describe properties– Collection of similar objects is a class
• Methods represent real world actions of classes
• Classes are organized in a class hierarchy– Inheritance is ability of object to inherit
attributes and methods of classes above it
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THE HIERARCHICAL MODEL
It defines data as and relationships through hierarchy of It defines data as and relationships through hierarchy of data values. This database model is the oldest database data values. This database model is the oldest database
model.model.A DBMS belonging to the hierarchical data model uses A DBMS belonging to the hierarchical data model uses
tree structures to represent relationship among records. tree structures to represent relationship among records. Tree structures occur naturally in many data Tree structures occur naturally in many data
organizations because some entities have an intrinsic organizations because some entities have an intrinsic hierarchical order. For example, an institute has a hierarchical order. For example, an institute has a
number of programmes to offer. Each program has a number of programmes to offer. Each program has a number of courses. Each course has a number of number of courses. Each course has a number of
students registered in it. The following figure depicts, students registered in it. The following figure depicts, the four entity types Institute, Program, Course and the four entity types Institute, Program, Course and
Student make up the four different levels of hierarchical Student make up the four different levels of hierarchical structure. The figure 1 shows an example of database structure. The figure 1 shows an example of database
occurrence for an institute. A database is a collection of occurrence for an institute. A database is a collection of database occurrence.database occurrence.
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Figure 1: A simple Hierarchy
• A hierarchical database therefore consists of a collection of records that are connected with each other through links. Each record is a collection of fields (attributes), each of which contains one data value. A link is an association between precisely two records.
Institute
Programme
Courses
Student
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• The hierarchical data model has the following features:– Each hierarchical tree can have only one root
record type and this record type does not have a parent record type.
– The root can have any number of child record types and each of which can itself be a root of a hierarchical sub tree.
– Each child record type can have only one parent record type
– Data in a parent record applies to all its children records
– A child record occurrence must have a parent record occurrence; deleting a parent record occurrence requires deleting its entire children record occurrence.
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• THE NETWORK MODELThe network data model was formalised in the late 1960s by the Database Task Group of the Conference on Data System Language (DBTG/ CODASYL). Their first report, which has been, revised a number of times, contained detailed specifications for the network data model (a model conforming to these specifications is also known as the DBTG data model). The specifications contained in the report and its subsequent revisions have been subjected to much debate and criticism. Many of the current database applications have been built on commercial DBMS systems using the DBTG model.
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The Relational ModelThe relational model is conceptually simple and
more importantly based on mathematical theory of relation. It also frees the users from details of storage structure and access methods.
The relational model like all other models consists of three basic components
A set of domains and a set of relationsOperation on relationsIntegrity rulesCONCEPTS OF A RELATIONAL MODELThe relational model was propounded by E.F. Codd
of the IBM in 1972. The basic concept in the relational model is that of a relation.A relation can be viewed as a table, which has the following properties:
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Property 1: it is column homogeneous. In other words, in any given column of a table, all items are of the same kind.Property 2: each item is a simple number or a character
string. That is, a table must be in 1NF. (First Normal Form) which will be introduced in the second unit.
Property 3: all rows of a table are distinct.Property 4: the ordering of rows within a table is immaterial.Property 5: the columns of a table are assigned distinct
names and the ordering of these columns is immaterial.Example of a valid relation
S# P# SCITY10 1 BANGALORE10 2 BANGALORE11 1 BANGALORE11 2 BANGALORE
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THE RELATIONAL COMPLETENESSThe notion of relational completeness was
propounded by Codd in 1972 as a basis for evaluating the power of different query languages.
A language is relationally complete if the basic relational algebra operations can be performed. The basic relational algebra operations are
UnionDifferenceGross productSelection
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• Object-based models It is a collection of real world objects
called entities and their relationships.It defines the database as a collection of objects and contains both data members/values and operation that are allowed on the data.The interrelationships and constraints are implemented through objects.
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