Database Management System

Table of Contents:-

• What is Database Management System?
• Objectives of DBMS
• Architecture of DBMS
• Components of DBMS
• Data Model
• Relational Data Model
• Difference between DBMS and RDBMS
• Network Data Model

What is Database Management System?

Data is one of the most important business assets. It is only valid when it is suitably managed. When data is properly collected, organised, analysed and processed, it transforms into information that can be utilised in business decisions. Organisations can only survive when they make optimised decisions in the highly competitive market.

The optimal business decisions can be made only if the organization can efficiently collect, organise, analyse and interpret data and get proper information. Now we can understand the importance of data management in all business operations. The data is efficiently managed in a database by using a database management system. The database management system is a software package which efficiently manages a database.

The database is created and maintained by an integrated set of programs termed the Database Management System (DBMS). Conveniently and effectively defining, storing, retrieving and manipulating the data contained in the database, is the major aim of the DBMS.

A Database Management System (DBMS) is a software tool used to perform various types of operations on Data in a database and creates a convenient and efficient environment which helps the user to access data easily, “The DBMS (Database Management System) is software that helps in efficient and convenient use of the database by utilizing and maintaining huge collections of data”.

Some commercial databases are ORACLE, INGRESS, MySQL, SYBASE etc. The image given below explains the overview of DBMS.

Objectives of DBMS

Objectives of DBMS are given below:

1) Shareability

The basic aim of the DBMS is the ability to share data resources. Shareability is the concept of different people and different processes processing the same genuine data at almost the same time. Below mentioned are the aims of the shareability:

i) Various user views of the same data stored are handled,

ii) Interconnected data is combined.

iii) The restart and recovery operations are synchronised among many users.

iv) Various kinds of people are aided by the changing levels of skill.

v) Standards are set.

vi) For maintaining data integrity, the concurrent updates are controlled.

2) Evolvability

With the growing user needs and technological advancements, the DBMS changes accordingly and this ability is referred to as evolvability. The future availability of the data resources is increased by evolvability. Both expansion and contraction are the constituents of evolvability.

These are the changes occurring in the system to fit the varying requirements and desires of the environment being used. The gradual unfolding, development and growth of a system to fulfil the requirements efficiently of the using environment are involved in the evolvability. Also, it includes the changes in the system according to the changing technology and requirements.

3) Integrity

The integrity of the database is used for:

i) Maintaining the quality of the database,

ii) Assuring the database’s privacy, and

iii) Protection of the existing database,

2) Availability

Availability means the required data of the organisation is brought to the users who need that data. The users (people within an organisation) should be able to access the system easily (which manages data resources which makes the data available to the users when and where required and in the manner and form in which it is required).

Architecture of DBMS

The image below represents the architecture of DBMS:

Components of DBMS

The common components of DBMS are explained below.

1) DML Pre-Compiler

 A DML pre-compiler converts DML statements embedded in an application program into regular functions within the host language. It must interact with the DML compiler to generate the appropriate code.

2) File Manager

The file manager’s task includes space allocation on disk storage and managing the data structure representing the stored information. It is implemented using an interface to the current file subsystem of the host computer, or it is included in a file subsystem written exclusively for the DBMS.

3) DDL Interpreter

DDL Interpreter: It interprets and converts DDL statements into a set of tables to record metadata, such as file names, data items, storage details for each file, mapping information, constraints, etc. The schema definitions specified in DDL statements are processed.

4) Database Manager

The database manager is a program module that interfaces low-level data and application programs and queries. It is responsible for interfacing with the file system.

5) Database Administrator (DBA)

This high-level function involves managing all data resources within an organization and includes the maintenance of corporate-wide data definitions and standards.

6) Query Processor

The query processor interprets the user’s queries and converts them into a form understandable by the data manager for further execution. It utilizes a data dictionary to identify the format of the relevant portion of the query. The query processor then uses this information to modify the query accordingly.

7) Data Dictionary

The data dictionary or data repository is a significant component of a DBMS, containing information about data, also known as metadata. It includes the database descriptions used by DBMSs, where the data dictionary is active (checking the database each time it is accessed) and integrated.

8) Buffer Manager

A buffer is where a block from a file is read. Buffer management aims to achieve optimal performance while minimizing the demand for CPU resources. When two or more buffers are used for a file, it facilitates data transfer related to data processing.

9) Storage Manager

It creates the interface between low-level data stored in the database, application programs, and queries. The main tasks of the storage manager include storage of data, retrieval, and updation.

10) Database Users

Database users are the end users who retrieve information from the database. They access the database for querying, updating, and generating reports.

Data Model

To describe the organisational structure of the database, various concepts are used. These sets of concepts are commonly known as data models. They also provide the essential means to get the abstraction.

The structure of a database includes:

1. Data Types,
2. Relationship, and
3. Constraints

These elements should hold for the data. For the specific retrievals and updates of the database, data models also have some operations.

When real-world entities, their constraints and relationships are logically organised, then it is known as a ‘data model’. For a data model, a database language is a concrete syntax.

A data model is implemented by a database.

A group of conceptual tools is known as a data model. It describes the:

1. Data.
2. Data relationships,
3. Data semantics, and
4. Data constraints.

Categories of Data Models

The main categories of data models are:

Categories of Data Models are listed as:

1. Relational Model
2. Hierarchical Model
3. Network Model
4. Entity-Relationship Model
5. Object-Oriented Model

Relational Data Model

To represent the data and relationships among them, this model uses the relations (group of tables), Every table has several attributes (columns) with unique names.

This model relates the records using the value of the relation. This model is conceptually straightforward and based on the mathematical theory of relation. This is one of the main advantages of the relational data model. In this, users need to worry more about the storage structure and access method.

For example, let’s consider a table (named wage) as a relational database.

Difference between DBMS and RDBMS

Concept	DBMS	RDBMS
Relation between tables	Programmatically maintained	Tables are used to store the station between tables and are stored in the same database.
Multi-User	Generally one can access the files simultaneously so DBMS does not support multiple users.	RDBMS supports multiple uses at a time.
Security of Data	Not supported	Security is implemented at the machine level
Table Storage	Predefine extensions are used to share each table and stored as a single file.	Single or multiple database files are used to store the tables, as they may belong to different users.
Access to Database Files	The stored files can be accessed directly by the users.	Low-level database files are protected from immediate access by users.
Distributed Database	Not supported.	Supported.
Abstract View	There is no support for abstract views derived from the base tables.	There is support for abstract views.
Codd’s Rules	Less than 8 rules are satisfied	More than 8 rules are satisfied

Network Data Model

The Network Data Model represents data as a collection of records and relationships among the data. These relationships are characterised by links, which can be viewed as pointers.

There are three basic components in the Network model; they are:

1) Record Type: A record type represents a finite number of similar-type entities.

2) Links: In the network data model, all relationships between the same or different record types are restricted to binary, many-one relationships. These many-one relationships are called links.

3) Data Elements: Entities are distinguished by the values of the data elements with which the corresponding record type is associated.

The overall logical structure of a database is represented by a directed graph. Nodes represent record types, and arcs represent links. If there is a relationship between two record types T₁ and T₂ and the relationship is many – one from T₁ to T₂, then an arc is drawn from the node T₁ to the node T₂.

This is described in the image given below.

Here, teachers and courses are two record types represented by two nodes. The relationships between them are many – one from courses to teachers (one teacher may be associated with more than one course but one course can be taught by at most one teacher). This relationship is represented by the direction from courses to teachers. If there is a many-many relationship between two record types T₁ and T₂ then this mary-many relationship cannot be expressed directly in this model. However, a many-many relationship can be expressed by splitting it into two many-one relationships. This is possible if a new record type (called a dummy record type) is introduced.

This is illustrated in the image below. Here, the many-many relationship between the two record types’ employees and projects is split into two many-one relationships, one is from work into employees and the other is from work into projects. The node work represents a newly introduced dummy record type. It is a dummy in the sense that it does not bear any significance as long as one is concerned with the type-level view.

For example, the network model for departmental stores is shown below.