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Solutions for Informatics Practices, Class 11, CBSE
Assertion (A): Database management system is an application software which arranges data in a well-organized manner in the form of tables.
Reasoning (R): DBMS acts as an interface between the database stored in the computer memory and the user.
Both A and R are true and R is the correct explanation of A.
Explanation
Database Management System (DBMS) is an application software that acts as an interface between the database stored in the computer memory and the user. It enables users to interact with the database and store data in a well-organized manner in the form of tables. The purpose of the DBMS software is to allow the user to create, access, modify, and control a database.
Assertion (A): In hierarchical model, the data is organized in a tree-like structure.
Reasoning (R): In hierarchical model, searching for a particular record is a time-consuming process.
Both A and R are true and R is the correct explanation of A.
Explanation
The hierarchical model arranges data in a tree structure, where each record has a parent-child relationship. Searching for a specific record in such a model may require traversing through multiple levels of the hierarchy, which is time-consuming.
Assertion (A): A database consists of multiple tables.
Reasoning (R): A foreign key is used to represent the relationship between two tables.
Both A and R are true and R is the correct explanation of A.
Explanation
In a database system, data is organized into multiple tables for better organization, management, and query efficiency. A foreign key is a non-key attribute whose value is derived from the primary key of another table in a database. It references the primary key in another table, thereby establishing a relationship between the two tables.
Assertion (A): The limitations of traditional file system are overcome by storing data in a database.
Reasoning (R): We can organize related data logically in a database.
Both A and R are true and R is the correct explanation of A.
Explanation
Traditional file systems have limitations such as data redundancy, inconsistency, and difficulties in data sharing and security. In contrast, databases store data in a structured and organized manner, which helps overcome these limitations. They allow us to logically organize related data, making data management, retrieval, and manipulation more efficient.
Assertion (A): The number of attributes in a relation is called the degree of the relation.
Reasoning (R): The number of tuples in a relation is called the cardinality of the relation.
Both A and R are true but R is not the correct explanation of A.
Explanation
The degree of a relation and the cardinality of a relation are two separate concepts in database management. The number of attributes or columns in a relation is called the degree of the relation, while the number of tuples or records in a relation is called the cardinality of the relation.
Assertion (A): Each table must have one primary key.
Reasoning (R): Primary key is a set of one or more attributes that uniquely identifies a tuple in a relation.
Both A and R are true and R is the correct explanation of A.
Explanation
In a database, each table can have only one primary key, which is unique and non-redundant in nature. The primary key is a set of one or more attributes or fields that uniquely identify a tuple or row in a relation.
Assertion (A): A database can have only one table.
Reasoning (R): If a piece of data is stored in two places in a database, it leads to wastage of storage space.
A is false but R is true.
Explanation
A database can have multiple tables. Data redundancy, which occurs when the same data is repeated in multiple places within a database, leads to wastage of storage space. A DBMS eliminates data redundancy by integrating files, ensuring that multiple copies of the same data are not stored.
What is a database?
Organized collection of data or information that can be accessed, updated and managed
Reason — Database is an organized collection of interrelated data or information that can be accessed, updated and managed.
Primary Key
Reason — A primary key is a set of one or more attributes/fields which uniquely identifies a tuple/row in a table.
Foreign Key
Reason — A foreign key is a non-key attribute whose value is derived from the primary key of another table.
Hierarchical
Reason — Hierarchical model depicts one-to-many (1:M) relationships between a parent and child segment. Each parent segment can have many child segments but it does not hold true the other way round-each child segment has only one parent segment and is connected through links.
Physical level
Reason — Physical level is the lowest level of abstraction that describes how the data is actually stored in the database.
Logical
Reason — Logical/Conceptual data independence is a kind of mechanism which is independent of the actual data stored on the disk. If any changes are made in the table format, it does not change the data residing on the disk.
Tuple, Attribute
Reason — Records are also known as tuple and fields are also known as attributes.
empid, ename, esalary
Reason — The field names empid, ename, and esalary
are valid and appropriate for a table named Employee because they are descriptive of employee attributes: employee ID, employee name, and employee salary.
Information is processed, organized, and meaningful data that has been analyzed, interpreted, and structured to provide context, relevance, and value. It is derived from data through analysis and is used to make decisions or gain insights.
Data | Information |
---|---|
Data is the lowest level of abstraction. | Information is one level higher abstraction than data. |
Data is unstructured and carries no meaning. | Information is derived by interpreting and processing data. |
For example, marks such as 67, 88, 90 and 77 are considered data. | For example, when these marks are related to a boy named Rohit, a student of class IX who has scored 67 in English, 88 in Maths, 90 in Physics and 77 in Chemistry then it becomes information. |
Database is an organized collection of interpreted data that serves many applications.
A Database Management System is a general-purpose software system that facilitates the process of defining, constructing and manipulating databases for various applications.
A database system in SQL consists of tables with rows and columns, a schema defining structure and relationships, SQL for interaction, indexes for performance, constraints for data integrity.
A Database Management System (DBMS) is a general-purpose software system that facilitates the process of defining, constructing and manipulating databases for various applications.
The database system is used to eliminate the problems of data redundancy and data inconsistency.
Database | File |
---|---|
Database is an organized collection of interpreted data that serves many applications. | A file is a collection of unorganized data stored in a single location. |
Data retrieval is fast and efficient, as databases use indexing and querying mechanisms. | Data retrieval is slow and inefficient, as the entire file needs to be searched. |
Data sharing is easy, as multiple users and applications can access the database simultaneously. | Data sharing is limited, as files are typically accessed by a single user or application. |
Data integrity is ensured through constraints, triggers, and transactions. | Data integrity is not ensured, as data can be corrupted or lost easily. |
Databases support relationships between data entities. | Files do not support relationships between data entities. |
Data | File |
---|---|
Data refers to raw facts, figures, or values that are collected and stored without any specific context or interpretation. | A file is a collection of unorganized data stored in a single location. |
The purpose of data is to convey information, provide insights, or support decision-making. | The purpose of a file is to store, manage, and provide access to the data. |
Data can exist in various formats, such as numbers, text, images, or audio, and can be structured or unstructured. | A file has a specific format and structure, defined by its file type (e.g., .txt, .jpg, .mp3), which determines how the data is stored and retrieved. |
The various components of the database system are described below:
The advantages of DBMS are as follows:
The disadvantages of DBMS are as follows:
The DBA or the Database Administrator is the person responsible for the security and functioning of the database.
With centralized control of the database, the DBA (Database Administrator) can ensure that all applicable standards are followed in the representation of data, i.e., format, documentation standards and conventions, etc.
Repetition (duplication) of the same data in multiple files is known as data redundancy. A DBMS eliminates data redundancy by integrating the files so that multiple copies of the same data are not stored.
Data abstraction is a process of hiding the implementation details (such as how the data is stored and maintained) and representing only the essential features to simplify user's interaction with the system.
The different levels of abstraction are:
Data independence is the ability to change the schema at one level of a database system without requiring changes at a higher level. This is achieved through metadata, which follows a layered architecture, ensuring that changes to data at one layer do not affect data at another layer. A database system provides two types of data independence:
Give the terms for each of the following:
(a) Collection of logically related records.
(b) DBMS creates a file that contains description about the data stored in the database.
(c) Attribute that can uniquely identify the tuples in a relation.
(d) Special value that is stored when actual data value is unknown for an attribute.
(e) An attribute which can uniquely identify tuples of the table but is not defined as primary key of the table.
(f) Software that is used to create, manipulate and maintain a relational database.
(a) Table
(b) Data dictionary
(c) Primary key
(d) NULL
(e) Alternate Key
(f) Database Management System (DBMS)
A null value can be entered in a foreign key, indicating that the records are not related. In certain situations, a foreign key may accept a NULL value if it's not a part of the primary key of the foreign table.
For example, consider an Orders table in a database. Each order may or may not be associated with a customer. If an order is placed by a guest or a new customer who hasn't been added to the system yet, the CustomerID foreign key in the Orders table can be NULL to indicate that there is no associated customer record for that order.
Database | Table |
---|---|
Database is an organized collection of interrelated data that serves many applications. | A table is a structure within a database that organizes data into rows and columns. |
It consists of multiple tables. | It is comprised of rows and columns. |
It is at higher level in the data storage hierarchy. | It is at lower level, as it is a component of the database. |
For example, MySQL database. | For example, employee table. |
Primary Key | Foreign Key |
---|---|
Primary Key is a column or group of columns in a table that uniquely identify every row in that table. | A foreign key is an attribute whose value is derived from the primary key of another table. A foreign key is used to represent the relationship between two tables. |
Primary key cannot have Null values. | Foreign key can have Null values. |
There can be only one primary key in a table. | Multiple foreign keys can exist in a table. |
It is used to enforce entity integrity and ensure data uniqueness. | It is used to enforce referential integrity and maintain data consistency across related tables. |
Degree of a relation | Cardinality of a relation |
---|---|
The number of attributes in a relation is called the Degree of the relation. | The number of tuples in a relation is called the Cardinality of the relation. |
For example, if a relation has attributes like Name, Age, and Address, then its degree is 3. | For example, if a relation contains 10 records or tuples, then its cardinality is 10. |
A database stores the data at a central location wherefrom all application programs can access data. This removes the need of saving own data by application program and thus it reduces data redundancy.
Suppose all customers of a particular business live in states of which the city name is unique. Given the following description for customer data:
CUST_ID, CUST_NAME, STREET, CITY, STATE, PHONE
(a) List the most likely key for the primary key.
(b) List all the candidate keys and alternate keys.
(a) The most likely primary key is CUST_ID because it is a unique identifier assigned to each customer.
(b) CUST_ID, CITY attributes can be considered as candidate keys as both are unique to each customer.
CITY can serve as an alternate key because all customers live in states where the city names are unique.
Relation file | Traditional file |
---|---|
Data organized in tables with rows and columns. | Data stored in unstructured formats. |
Supports structured querying with SQL. | Lacks standardized querying abilities. |
Allows for defining relationships between tables. | No inherent support for relationships. |
Offers flexibility in data storage and retrieval. | Limited flexibility in data organization. |
Examples : MySQL, PostgreSQL | Examples : Text files, CSV files, Excel spreadsheets |
A database is an organized collection of interrelated data that serves many applications, while a table is a collection of logically related records. In other words, it is a named collection of data items that represent a complete unit of information within a database.
A Database Management System (DBMS) is a general-purpose software system that facilitates the process of defining, constructing and manipulating databases for various applications.
Examples of DBMS are MS Access, MySQL.
A primary key is a set of one or more attributes/fields which uniquely identifies a tuple/row in a table.
Its function in a table is to uniquely identify tuples or rows and prevent the entry of duplicate rows, thus ensuring data integrity.
Row | Column |
---|---|
A horizontal group of data cells in a table. | A vertical group of data cells in a table. |
Each row in a table is known as a tuple/record. | Each column in a table is known as field/attribute. |
A record in a table represents a set of related data. | An attribute is a set of values of a particular type. |
The total number of rows in a table represent its cardinality. | The total number of columns in a table represent its degree. |
Database | Table |
---|---|
Database is an organized collection of interrelated data that serves many applications. | A table is a structure within a database that organizes data into rows and columns. |
It consists of multiple tables. | It is comprised of rows and columns. |
It is at higher level in the data storage hierarchy. | It is at lower level, as it is a component of the database. |
For example, MySQL database. | For example, employee table. |
False
Reason — An alternate key is a candidate key. A candidate key that is not chosen as the primary key is called an alternate key. In other words, any attribute that is a candidate for the primary key, i.e., which is capable of becoming a primary key but is not a primary key, is an alternate key.
True
Reason — Data redundancy occurs when the same data is stored in multiple locations. This can lead to data consistency issues because if the data is updated in one location, it may not be updated in all other locations, resulting in inconsistent data across the system.