Introduction to DBMS

    DBMS (Database Management System)

•  A Database Management System (DBMS) is a software designed to store, retrieve, define, and manage data in a database.

•  ‍DBMS software primarily functions as an interface between the end user and the database, simultaneously managing the data, and the database schema in order to facilitate the organization and manipulation of data.

•   A database management system functions through the use of system commands, first receiving instructions, then instructing the system accordingly, either to retrieve data, modify data, or load existing data from the system.

Difference between Data & Information in DBMS

• Data is raw, unprocessed, unorganized facts that are seemingly random and do not yet carry any significance or meaning.

• Information refers to data that has been organized, interpreted, and contextualized by a human or machine so that it possess relevance and purpose.

• Information is filtered data that has been made systematic and useful, and is considered to be more reliable and valuable to researchers as proper analysis and refinement has been conducted.

    File System Vs DBMS

    File System:

•       The file system is basically a way of arranging the files in a storage medium like a hard disk.

•       The file system organizes the files and helps in the retrieval of files when they are required.

•       File systems consist of different files which are grouped into directories.

•       The directories further contain other folders and files.

•       The file system performs basic operations like management, file naming, giving access rules, etc.

    DBMS:

•       Database Management System is basically software that manages the collection of related data.

•       It is used for storing data and retrieving the data effectively when it is needed.

•       It also provides proper security measures for protecting the data from unauthorized access.

•       In Database Management System the data can be fetched by queries and relational algebra.

•       It also provides mechanisms for data recovery and data backup. 

Introduction of 3-Tier Architecture in DBMS

        DBMS 3-tier architecture divides the complete system into three inter-related but independent                modules as shown below:

        Physical Level:

•       At the physical level, the information about the location of database objects in the data store is kept.

•       Various users of DBMS are unaware of the locations of these objects.

•       In simple term, physical level of a database describes how the data is being stored in secondary storage devices like disks and tapes.

        Conceptual Level:

•       At conceptual level, data is represented in the form of various database tables.

•       For Example, STUDENT database may contain STUDENT and COURSE tables which will be visible to users but users are unaware of their storage.

•       Also referred as logical schema, it describes what kind of data is to be stored in the database.

        External Level: 

•       An external level specifies a view of the data in terms of conceptual level tables. 

•       Each external level view is used to cater to the needs of a particular category of users.

•       For Example, FACULTY of a university is interested in looking course details of students, STUDENTS are interested in looking at all details related to academics, accounts, courses and hostel details as well.

•       So, different views can be generated for different users.

•       The main focus of external level is data abstraction.

    Difference between Schema and Instance in DBMS

    Instances:

•       Instances are the collection of information stored at a particular moment.

•       The instances can be changed by certain CRUD (Create, Read, Update, Delete) operations as like addition, deletion of data.

    Example –

Let’s say a table TEACHER in our database whose name is SCHOOL, suppose the table has 50 records so the instance of the database has 50 records for now and tomorrow we are going to add another fifty records so tomorrow the instance has total 100 records. This is called an instance.

     Schema :

•       Schema is the overall description of the database.

•       The basic structure of how the data will be stored in the database is called schema.

    Example –

    Let’s say a table named TEACHER in our database name SCHOOL, the TEACHER table require the     name, dob, doj in the table so we design a structure as: 

                        TEACHER

                        name: varchar  doj: date                       dob: date

    Above given is the schema of the table TEACHER.

      Data Independence

• Data independence can be explained using the three-schema architecture.
• Data independence refers characteristic of being able to modify the schema at one level of the database system without altering the schema at the next higher level.
• There are two types of data independence:

            (1) Logical Data Independence and     (2) Physical Data Independence

     Logical Data Independence:

•      Logical data independence refers characteristic of being able to change the conceptual schema without having to change the external schema.

•       Logical data independence is used to separate the external level from the conceptual view.

•       If we do any changes in the conceptual view of the data, then the user view of the data would not be affected.

•       Logical data independence occurs at the user interface level.

     Physical Data Independence:

•       Physical data independence can be defined as the capacity to change the internal schema without having to change the conceptual schema.

•    If we do any changes in the storage size of the database system server, then the conceptual structure of the database will not be affected.

•       Physical data independence is used to separate conceptual levels from the internal levels.

•       Physical data independence occurs at the logical interface level.

     Database Models

     •       Data Model gives us an idea that how the final system will look like after its complete         implementation.

•              It defines the data elements and the relationships between the data elements.

•       Data Models are used to show how data is stored, connected, accessed and updated in the     DBMS.

•       Some of the Data Models in DBMS are:

v  Hierarchical Model,                                         

v  Network Model,                                  

v  Entity-Relationship Model,                              

v  Relational Model,                                

v  Flat Data Model,                                              

v  Object-Oriented Data Model,

v  Context Data Model,                                      

v  Associative Data Model,

v  Object-Relational Data Model,                         

v  Semi-Structured Data Model etc.

     Hierarchical Model

•       Hierarchical Model was the first DBMS model.

•       This model organizes the data in the hierarchical tree structure.

•       The hierarchy starts from the root which has root data and then it expands in the form of a tree adding child node to the parent node.

•       This model easily represents some of the real-world relationships like hierarchy of any organization, sitemap of a website etc.

 Example: 

Network Model

•       This model is an extension of the hierarchical model.

•       It was the most popular model before the relational model.

•       This model is the same as the hierarchical model, the only difference is that a record can have more than one parent.

•       It replaces the hierarchical tree with a graph.

 Example: In the example below we can see that node student has two parents i.e. CSE Department and Library. This was earlier not possible in the hierarchical model.

     Entity-Relationship Model

•       Entity-Relationship Model or simply ER Model is a high-level data model diagram.

•       In this model, we represent the real-world problem in the pictorial form to make it easy for the stakeholders to understand.

•       It is also very easy for the developers to understand the system by just looking at the ER diagram.

•       We use the ER diagram as a visual tool to represent an ER Model.

•       ER diagram has the following three components: Entity, Attribute and Relationship.

    Relational Model

•       This model was introduced by Dr. E. F. Codd in 1970.

•       Relational Model is the most widely used model.

•       In this model, the data is maintained in the form of a two-dimensional table.

•       All the information is stored in the form of rows and columns.

•       The basic structure of a relational model is tables.

•       So, the tables are also called relations in the relational model. 

    DBMS Vs RDBMS

     The below table demonstrates the main difference between RDBMS and DBMS: