What is Data?
“Raw facts or values that have no meaning by themselves.
Simple Example: 101, Rahul, 20, BCA
What is Information?
“Processed and organized data that has meaning and is useful for decision-making.
Simple Example:
- Student ID: 101
- Student Name: Rahul,
- Age: 20
- Studying: B.sc. CA&IT
What is Database?
A database is an organized collection of data”.
“A database is a collection of information that is organized so that it can easily be accessed, managed, and updated.”
“You can think of a database as an electronic filing system.”
Database Example
The college stores thousands of student records in software like Oracle, MySQL, or SQL Server.
Example:
College Database
│
├── Student Table
├── Faculty Table
├── Course Table
├── Fees Table
├── Examination Table
└── Library Table
Relationship between Data, Information, and Database
Raw Data
│
▼
Processing & Organization
│
▼
Information
│
Stored in
▼
Database
Operation of database
Users of the system can perform a variety of operations involving the files.
for example:
- Adding new files to database.
- Inserting data into existing files.
- Retrieving data from existing files.
- Deleting data from existing files.
- Removing existing files from the database.
Benefits of database
Compactness: There is no need for possibly huge paper files.
Speed: The machine can retrieve and update data far faster than a human.
Less Work: The task of maintaining files by hand is eliminated. Mechanical task has replaced it.
Accurracy: Accuracy, up-to-date information is available on demand at any time.
Protection: The data can be better protected against unintentional loss and unlawful access.
Centralized control: For multi-user system, database provides the centralized control.
What is DBMS?
Database system is a computerized record keeping system whose overall purpose is to store information and to allow users to retrieve and update that information on demand.
Facilities like adding and removing files, retrieving data from and updating data in such files or tables are provided by DBMS.
Components of DBMS
The four major components of database system are:
- Data
- Hardware
- Software
- Users.
Data in the database are of 2 types:
Integrated data means the database that is the combination of several distinct files, The redundancy among those files is partly or fully eliminated.
Shared data means the database can be shared among different users.
Different users can have access to the database at the same time. This is called concurrent access.
The hardware component of the system consist of :
The secondary storage volumes – typically magnetic tapes- that are used to hold the stored data, together with the associated I/O devices (disk drives, etc), device controllers, I/O channels and so forth.
The hardware processor and associated main memory that are used to support the execution of the database system software.
Software is a layer between the physical database and the users of the system.
It is known as a database manager or database server or Database Management System (DBMS).
All request to access the database are handled by the DBMS.
Facilities like adding and removing files, retrieving data from and updating data in such files or tables are provided by DBMS.
Users are divided into 3 classes:
First, are the application programmers who develop the database application programs in some programming languages.
Second, are the end users who do not have any formal training in IT, but access the database interactively via; online application, or via; the interface provided as an integral part of the system.
Third class of users are the database administrator or DBA. They decide the policies for maintaining and dealing with the data once it is stores.
What is DBA?
A technical person responsible for implementing the data administrator’s decision is the database administrator.
Database Administrator (DBA) is a person who has the central responsibility for the database.
It is the job of data administrator to decide what data should be stored in the database. DBA also establishes policies for maintaining and dealing with that data once it has been stored. Eg: data security policy.
DBA decided which user can perform what operations on what data in what circumstances. Without this control, it would be possible for one user to update the database incorrectly, and hence generating a wrong data for other users.
What is RDBMS?
A relational Database Management System (RDBMS) is a database management system (DBMS) that is based on relational model as introduced by Dr. Edgar F. Codd.
A DBMS should satisfy all 12 rules, but in practice there is no DBMS that satisfies all these rules.
Eg. of RDBMS are: Oracle, Microsoft SQL Server, Sybase SQL Server, and IBM’s DB2.
The most commonly used free RDBMS are MySQL, PostgreSQL.
All modern database management systems like SQL, MS SQL Server, IBM DB2, ORACLE, My-SQL and Microsoft Access are based on RDBMS.
Codd’s Rules for RDBMS
Dr. E.F. Codd is an IBM researcher who first developed the relational data model in 1970.
In 1985 he published a list of 12 rules that define an ideal relational database and has provided a guideline for the design of all relational database systems.
Rule 1: The information rule:
All data should be presented in the cell of table form.
Rule 2: The guaranteed access rule:
All data should be accessible without ambiguity [uncertainty]. This can be accomplished through a combination of the table name, primary key[row], and attributes[column name].
Rule 3: Systematic treatment of null values:
A field should be allowed to remain empty. This involves a support of a null value, which is distinct from an empty string or a number with a value of zero. (Apart from primary key). Sometimes it support a concept of not-null field constraint that prevents null values in a specific table column.
Rule 4: Dynamic online catalog based on the relational model:
In the Database Management Systems ‘metadata’ is the data about the database. The active online catalog that stores the metadata is called ‘Data dictionary’. That is called data dictionary is accessible only by authored users who have the required privileges.
Rule 5: The comprehensive data sublanguage rule:
The system must support a least one relational language that functionality for data definition, data manipulation, data integrity and database transaction control.
All RDBMS should use forms of standard SQL.
Rule 6: The view updating rule:
Data can be presented in different logical combinations called views. Each view should support the same full range of data manipulation that has direct access to a table available. Update and delete access to logical views is not fully supported by any current database.
Rule 7: High-level insert, update, and delete:
The INSERT, UPDATE, and DELETE operations should be supported for any retrievable set rather than just for a single row in a table.
Rule 8: Physical data independence:
The user is isolated from physical method of storing and retrieving information from the database. Changes are made to underlying architecture (hardware, disk storage methods) without affecting how the user accesses it.
Rule 9: Logical data independence:
How data is viewed should not be changed when logical structure of database changes. This rule is difficult to satisfy. Most database rely on strong ties between the data viewed and the actual structure of the underlying tables.
Rule 10: Integrity independence:
The database language (like SQL) should support constraints on user input that maintain database integrity. This rule is not fully implemented by most major vendors.
The 2 constraints that are preserved are:
1) No component of a primary key can have null value.
2) If a foreign key is defined in one table, any value in it must exist as a primary key in another value.
Rule 11: Distribution independence:
A user should be totally unaware of whether or not the database is distributed. (whether parts of the database exist in different location). This rule is difficult to implement.
Rule 12: Non subversion rule:
The database structure should not be modified in any way other than through the multiple row database language (like SQL).
Most database support administrative tool that allow some direct manipulation of the data structure.
Codd’s Rules Example
A Student table: You can retrieve a student's course using:
SELECT Course FROM Student WHERE StudentID = 101;
This follows Codd's Rule 2 (Guaranteed Access).
DBMS v/s RDBMS
Naming Conventions
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