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What is Model & data Model?

A model is a representation of ‘real world’ objects and events, and their associations. Models helps in abstraction that focuses on the important details & ignores the other aspects of the system

Data models define how data is connected to each other and how it is processed and stored inside the system.

The purpose of a data model is to represent data and to make the data understandable.

Components of Data Models

STRUCTURAL PART

It consists of rules that define the database and its structure

MANIPULATIVE PART

This part contains the type of operations that are allowed on the data eg. insertion, deletion, update etc.

INTEGRITY CONSTRAINTS

This part contains the set of constraints to make sure that data is accurate & valid.

Object based data models

Object based data models use Entities , Attributes & Relationships to describe the model.

ER-Model

Entity : An object (person, place, thing, concept, event) which is of some importance to an organization

Attribute : It describes the entity i.e. properties of an entity that is to be recorded.

Relationship : Association between the entities.

Record Based Data Models

Record based data models are based on fixed format records consisting of number of fields.

Relational Model

Relational Model is based on mathematical relations.
In this model data and relationships are represented in the form of tables, each of which has number of columns with unique name.

Users see the whole database in the form of tables. Such representation is only limited to the external and conceptual levels.

Relation : Tables.
Tuple : Single Row.
Key : Can be single or multiple attribute which
establishes & identifies relationships.
Attribute Domain : Value Scope of Attribute

Hierarchical Model

In this model data is organized in a tree like structure.

In a hierarchical database, an entity type can be either a parent or a child; under each individual entity is more multiple entities.

Entity types are related to each other using tree mapping, which is represented by one parent with many child relationships. There are also attributes of a specific data recorded under an entity.

Network Model

In this model data is organized in a tree like structure and it is the enhanced version of hierarchical model.

This data model is also represented as hierarchical, but this model will not have single parent concept. Any child in the tree can have multiple parents here.

The post Different Data Models in DBMS, ER Model, Relational Model appeared first on Iravati Solutions.

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There are four distinct types of people that participate in the DBMS environment: data and database administrators, database designers, application developers, and the end-users. 

Data Administrators

The database and the DBMS are corporate resources that must be managed like any other resource. The Data Administrator (DA) is responsible for defining data elements, data names and their relationship with the database.They are also known as Data Analyst.

Database Administrators (DBA)

A Database Administrator (DBA) is an IT professional who works on creating, maintaining, querying, and tuning the database of the organization. They are also responsible for maintaining data security and integrity. A DBA has many responsibilities. A good performing database is in the hands of DBA.

DBA Responsibilities

The life cycle of database starts from designing, implementing to administration of it. A database for any kind of requirement needs to be designed perfectly so that it should work without any issues.
Once all the design is complete, it needs to be installed. Once this step is complete, users start using the database. The database grows as the data grows in the database. When the database becomes huge, its performance comes down.
Also accessing the data from the database becomes challenge. These administration and maintenance of database is taken care by database Administrator – DBA.

Installing and upgrading the DBMS Servers

DBA is responsible for installing a new DBMS server for the new projects. He is also responsible for upgrading these servers as there are new versions comes in the market or requirement.

Design and implementation

He should be able to decide proper memory management, file organizations, error handling, log maintenance etc for the database.

Performance Tuning

Since database is huge and it will have lots of tables, data, constraints and indices, there will be variations in the performance from time to time.
It is responsibility of the DBA to tune the database performance.

Backup & Recovery

Proper backup and recovery programs needs to be developed by DBA and has to be maintained him. This is one of the main responsibilities of DBA. Data should be backed up regularly so that if there is any crash, it should be recovered without much effort and data loss.

Documentation

DBA should basically maintain all his installation, backup, recovery, security methods. He should keep various reports about database performance.

Security

DBA is responsible for creating various database users and roles, and giving them different levels of access rights.

Database Designers

Logical Database Designers

The logical database designer is concerned with identifying the data (that is, the entities and attributes), the relationships between the data, and the constraints on the data that is to be stored in the database.

The logical database designer must have a thorough and complete understanding of the organization’s data and any constraints on this data.

Physical Database Designers

The physical database designer decides how the logical database design is to be physically realized.

• mapping the logical database design into a set of tables and integrity constraints.
• selecting specific storage structures and access methods for the data to achieve good
  performance.

Application Developers

Once the database has been implemented, the application programs that provide the required functionality for the end-users must be implemented. This is the responsibility of the application developers.

They are the developers who interact with the database by means of DML queries. These DML queries are written in the application programs like C, C++, JAVA, Pascal etc.

End Users

The end-users are the ‘clients’ for the database, which has been designed and implemented, and is being maintained to serve their information needs.

Sophisticated Users

The sophisticated end-user is familiar with the structure of the database and the facilities offered by the DBMS.

Naive Users

These are the users who use the existing application to interact with the database. For example, online library system, ticket booking systems, ATMs etc

The post Roles in DBMS Environment, DBA Role, Database Designers appeared first on Iravati Solutions.

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Why 3-level architecture?

Each user should be able to access the same data, but with its own customized view.

User need not have to deal with physical structure of database directly.

DBA should be able to make changes to physical structure without affecting the user view.

The database internal structure should be unaffected by changes made to physical storage.

3- level architecture

EXTERNAL LEVEL

User’s view of the database. This level shows the view that is relevant to the specific user i.e. hiding the unrelated
details. Only those entities , attributes & relationships are shown which are relevant to the specific user. Different views with different representation of same data

CONCEPTUAL LEVEL

Community view of the database i.e. whole database for community of users. It contains the logical structure of database as viewed by the DBA.

Entities, Attributes & their Relationships

Data Constraints

Security & Integrity Information

Conceptual level supports each user view. This level hides the physical storage structure & focuses on data entities, attributes & relationships.

INTERNAL LEVEL

Low level physical and actual representation of database. This level tells about how the data is stored in secondary storage devices like disks etc. Storage Space Allocations for data. Data Compression & Encryption. Data Structures and File Organization used to store data.

int empid;
char Name[20];
char Department[15];
float salary

Database Schema

Overall design & description of database is called database schema.

It is a skelton structure which represents logical view of entire database.

EXTERNAL SCHEMA, CONCEPTUAL SCHEMA, INTERNAL SCHEMA

DATABASE INSTANCE

Status of a database at particular instant of time. DBA might create multiple instances of the same database for different purposes.

Mapping between schema

Conceptual / Internal Mapping

The conceptual schema of database is related (mapped) with internal schema with the help of conceptual / internal mapping. This helps the DBMS to find actual records in physical storage that can be represented
as logical record in conceptual schema.

External / Conceptual Mapping

The external schema of database is related (mapped) with conceptual schema with the help of external / conceptual mapping. This helps the DBMS to take relevent information from conceptual schema and show
to the particular user.

Data Independence

This is one of the major objective of 3-level architecture. Data Independence means that the upper levels in DBMS are unaffected by the changes made at the lower levels.

Logical Data Independence : It means that the external schemas are not affected by the changes made to the conceptual schema.

Changes to the conceptual schema, such as the addition or removal of new entities, attributes, or relationships, should be possible without having to change existing external schemas or having to rewrite application programs.

Physical Data Independence : It means that the conceptual schema is not affected by the changes made to the internal schema.

Changes to the internal schema, such as using different file organizations or storage struc- tures, using different storage devices, modifying indexes, or hashing algorithms, should be possible without having to change the conceptual or external schemas.

The post 3-Tier DBMS Architecture and Data Independence appeared first on Iravati Solutions.

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Limitations of File Based System

SEPARATION & ISOLATION OF DATA

It is difficult to access the data which is isolated and stored in separate files. Imagine we have to generate a single report of student, who is studying in particular class, his study report, his library book details, and hostel information. All these informations are stored in different files. How do we get all these details in one report?

DUPLICATION OF DATA (REDUNDANCY)

There is uncontrolled duplication of data in the file-based approach. Duplication is waste of space and it costs time and money to enter the data more than once.Additional space requirements leads to additional costs.Duplication of data means that the data is no longer consistent which leads to Loss of Data Integrity.

LOSS OF DATA INTEGRITY

Imagine Student Details and Student_ReportCard files have student’s address in it, and there was a change request for one particular student’s address.
The program searched only Student Details file for the address and it updated it correctly.
There is another program which prints the student’s report and mails it to the address mentioned in the Student_ReportCard file.
What happens to the report of a student whose address is being changed? There is a mismatch in the actual address and his report is sent to his old address. This mismatch in different copies of same data is called data inconsistency (loss of data integrity).

DATA DEPENDENCE

The data stored in file depends upon the application program through which the file was created. It means that the structure of data files is coupled with application program.

INCOMPATIBLE FILE FORMATS

The structure of files are dependent on the application programming languages. The structure of a file generated by a PYTHON program may be different from the structure of a file generated by a ‘C’ program. The incompatibility of such files makes them difficult to process jointly.

FIXED QUERIES OF PROGRAMS

File-based systems are very dependent upon the application developer, who has to write any queries or reports that are required. There was no facility for asking unplanned queries about the data or about the type of data available.

Advantages of Dbms

CONTROL OF DATA REDUNDANCY

DBMS tries to eliminate the redundancy by integrating the files so that multiple copies of the same data are not stored. DBMS does not remove the duplication entirely but can control the amount of duplication. Sometimes it is important to duplicate key data to model relationships, improve performance.

DATA CONSISTENCY

By eliminating or controlling redundancy, we reduce the risk of inconsistencies occurring.If a data item is stored only once in the database, any update to its value has to be per- formed only once and the new value is available immediately to all users. If a data item is stored more than once and the system is aware of this, the system can ensure that all copies of the item are kept consistent.

SHARING OF DATA

Database is a shared resource which can be shared with different authorized departments. New applications can build on the existing data in the database and add only data that is not currently stored, rather than having to define all data requirements again.

IMPROVED DATA INTEGRITY

Database integrity refers to the validity and consistency of stored data. Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate.

IMPROVED SECURITY

DBMS protects the database from the unauthorized users. This may take the form of user names and passwords to identify people authorized to use the database. The access that an authorized user is allowed on the data may be restricted by the operation type (retrieval, insert, update, delete).

INCREASED CONCURRENCY

DBMS ensures concurrent data access so that there is no loss of information. DBMS provide access to multiple users to access the database at the same time.

IMPROVED BACKUP & RECOVERY

Backup and recovery in general refers to the various strategies and operations involved in protecting your database against data loss and reconstructing the data should that loss occur.

DATA INDEPENDENCE

DBMS separates the data descriptions from the applications, thereby making applications immune to changes in the data descriptions. This is known as data independence.

It refers to the immunity of user applications to changes made in the definition and organization of data

Disadvantages of Dbms

The post DBMS Advantages and Disadvantages, Limitations of File Systems appeared first on Iravati Solutions.

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———————–
Questions covered in the lecture:-
———————–
What is Data?
What is Information?
What is Difference between Data and Information?
What is Traditional/File based approach?
What is Database?
What is DBMS and DBMS Environment?
—————–
Lecture Overview
——————
Data is raw, unorganized facts that lacks any kind of meaning and needed to be processed. Data can be anything that can be recored; like Numbers, Text, Images, Videos, etc. Data must be interpreted in order to derive any meaning, so basically it is meaningless.

Processed data is Information. When the data is processed, organized, structured within a given context to give it a meaning, it is called information.

‘File-based approach‘ refers to the situation where data is stored in one or more separate computer files defined and managed by different application programs.

File-based systems were an early attempt to computerize the manual filing system that we are all familiar with.

Database: A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organization.

Shared : The database is no longer owned by one department but is a shared corporate resource.

Collection : It is a huge collection of data.

Description of data : The database also holds the “Data about the data” i.e. metadata. Example : For any file :- author, date created, date modified, and file size

Logically Related : A relevant and related data in some context i.e. Entities, Attributes & Relationships.

DBMS: A software system that enables users to define, create, maintain, and control access to the database.

DBMS provides an interface to perform various operations like database creation, storing data in it, updating data, creating a table in the database and a lot more.

The post Introduction to DBMS – Basics, Data and Information, Database and DBMS (Lecture-01) appeared first on Iravati Solutions.