Database Concepts Class 11 Notes
Manual Record Keeping System :
A System where records are maintained by hand, without using a computer system.
Advantages of Manual Record Keeping System :
- It is less expensive.
- Less risk of data loss.
- No software specialised person is required.
Disadvantages of Manual Record Keeping System :
- No sharing of data.
- More chances of inconsistent data.
- Making correction is very time consuming.
Electronic Record Keeping System :
A System in which records are maintained in computer system instead of in paper.
Advantages of Electronic Record Keeping System :
- Less paper wastage.
- Searching of record is very simple.
- Easy to backup the documents.
Disadvantages of Electronic Record Keeping System :
- More expensive.
- More risk to data loss.
- A Software specialised person is required to manage this system.
Database Management System :
A database management system (DBMS) is a software that can be used to create and manage databases. Some examples of open source and commercial DBMS include MySQL, Oracle, PostgreSQL, SQL Server, Microsoft Access, MongoDB etc.
Databases are widely used in various fields. Some applications are given below :
Common Terms used in DBMS :
Attributes : The columns of a relation are the attributes which are also referred as fields. for example : In the table “Student” given below, there are four attributes.
Tuple : Each row of data in a relation (table) is called a tuple. It is also known as record. for example In the table “Student” given above, there are two tuples.
Domain : It is a set of values from which an attribute can take a value in each row. Usually, a data type is used to specify domain for an attribute. For example, in “Student” relation given above, the attribute Roll_no takes integer values and hence its domain is a set of integer values.
Degree : The number of attributes in a relation is called the Degree of the relation. For example, the relation “Student” given below with four attributes is a relation of degree 4.
Cardinality : The number of tuples in a relation is called the Cardinality of the relation. For example, the cardinality of relation “Student” is 2 as there are 2 tuples in the table.
Key Concepts in DBMS :
Database Schema : It is the skeleton of the database that represents the structure (table names and their fields/columns), the type of data each column can hold, constraints on the data to be stored (if any), and the relationships among the tables.
Data Constraint : Certain restrictions or limitations on the type of data that can be inserted in one or more
columns of a table during table creation is called data constraint. Constraints are used to ensure accuracy and
reliability of data in the database.
Meta-data or Data Dictionary :The database schema along with various constraints on the data is stored by DBMS in a database catalog or dictionary, called meta-data. A meta-data is data about the data.
Database Instance : When we define database structure or schema, state of database is empty i.e. no data entry is there. After loading data, the state or snapshot of the database at any given time is the database instance.
Query : A query is a request to a database for obtaining information in a desired way. Query can be made to get data from one table or from a combination of tables.
Data Manipulation : Modification of database consists of three operations viz. Insertion, Deletion or Update. Insertion means adding a new record in a table. Deletion means removing an existing record from a table. Updation means editing an existing record in a table.
Database Engine : Database engine is the underlying component or set of programs used by a DBMS to create database and handle various queries for data retrieval and manipulation.
Three Important Properties of a Relation :
In relational data model, following three properties are observed with respect to a relation which makes a relation different from a data file or a simple table.
Property-1 : imposes following rules on an attribute of the relation.
- Each attribute in a relation has a unique name.
- Sequence of attributes in a relation is immaterial.
Property-2 : imposes following rules on tuple of the relation.
- Each tuple in a relation is distinct.
- Sequence of tuples in a relation is immaterial.
Property-3 : imposes following rules on the state of a relation.
- All data values in an attribute must be from the same domain (same data type).
- Each data value associated with an attribute must be atomic.
- No attribute can have many data values in one tuple.
- A special value “NULL” is used to represent values that are unknown.
Keys in Relational Database :
Candidate Key : Those fields which can act as a primary key in a table are called Primary Key.
Primary Key : A field which uniquely identifies each and every record in table is called primary key.
Composite Primary Key : If no single attribute in a relation is able to uniquely identifies the tuples, then more than one attribute are taken together as primary key. Such primary key consisting of more than one attribute is called Composite Primary key.
Foreign Key : A foreign key is used to represent the relationship between two relations. A foreign key is an attribute whose value is derived from the primary key of another relation.
In some cases, foreign key can take NULL value if it is not the part of primary key of the foreign table. The relation in which the referenced primary key is defined is called primary relation or master relation.
SUMMARY A file in a file system is a container to store data in a computer. File system suffers from Data Redundancy, Data Inconsistency, Data Isolation, Data Dependence and Controlled Data sharing. Database Management System (DBMS) is a software to create and manage databases. A database is a collection of tables. Database schema is the design of a database. A database constraint is a restriction on the type of data that that can be inserted into the table. Database schema and database constraints are stored in database Catalog. Whereas the snapshot of the database at any given time is the database instance. A query is a request to a database for information retrieval and data manipulation (insertion, deletion or update). It is written in Structured Query Language (SQL). Relational DBMS (RDBMS) is used to store data in related tables. Rows and columns of a table are called tuples and attributed respectively. A table is referred to as a relation. Destructions on data stored in a RDBMS is applied by use of keys such as Candidate Key, Primary Key, Composite Primary Key, Foreign Key. Primary key in a relation is used for unique identification of tuples. Foreign key is used to relate two tables or relations. Each column in a table represents a feature (attribute) of a record. Table stores the information for an entity whereas a row represents a record. Each row in a table represents a record. A tuple is a collection of attribute values that makes a record unique. A tuple is a unique entity whereas attribute values can be duplicate in the table. SQL is the standard language for RDBMS systems like MySQL
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