Relational Database Operators

Relational Set Operators uses relational algebra to manipulate contents in a database. All together there are eight different types of operators. These operators are SQL commands.
SELECT is the command to show all rows in a table. It can be used to select only specific data from the table that meets certain criteria. This command is also referred to as the Restrict command.

UNION. It combines all of the rows in one table with all of the rows in another table except for the duplicate tuples. The tables are required to have the same attribute characteristics for the Union command to work. The tables must be union-compatible which means that two tables being used have the same amount of columns and the columns have the same names, and also need to share the same domain.

INTERSECT is the second SQL command that takes two tables and combines only the rows that appear in both tables. The tables must be union-compatible to be able to use the Intersect command or else it won't work.

DIFFERENCE in another SQL command that gets all rows in one table that are not found in the other table. Basically it subracts one table from the other table to leave only the attributes that are not the same in both tables. For this command to work both tables must be union-compatible.

PRODUCT command would show all possible pairs of rows from both tables being used. This command can also be referred to as the Cartesian Product.

PROJECT is the command that gives all values for certian attributes specified after the command. It shows a vertical view of the given table.

JOIN takes two or more tables and combines them into one table. This can be used in combination with other commands to get specific information. There are several types of the Join command. The Natural Join, Equijion, Theta Join, Left Outer Join and Right Outer Join

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Codd's Rule

Codd's Rule for Relational DBMS

E.F Codd was a Computer Scientist who invented the Relational model for Database management. Based on relational model, the Relational database was created. Codd proposed 13 rules popularly known as Codd's 12 rules to test DBMS's concept against his relational model. Codd's rule actualy define what quality a DBMS requires in order to become a Relational Database Management System(RDBMS). Till now, there is hardly any commercial product that follows all the 13 Codd's rules. Even Oracle follows only eight and half(8.5) out of 13. The Codd's 12 rules are as follows.

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Rule zero

This rule states that for a system to qualify as an RDBMS, it must be able to manage database entirely through the relational capabilities.

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Rule 1: Information rule

All information(including metadata) is to be represented as stored data in cells of tables. The rows and columns have to be strictly unordered.

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Rule 2: Guaranted Access

Each unique piece of data(atomic value) should be accesible by : Table Name + Primary Key(Row) + Attribute(column).
NOTE: Ability to directly access via POINTER is a violation of this rule.

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Rule 3: Systematic treatment of NULL

Null has several meanings, it can mean missing data, not applicable or no value. It should be handled consistently. Also, Primary key must not be null, ever. Expression on NULL must give null.

Rule 4: Active Online Catalog

Database dictionary(catalog) is the structure description of the complete Database and it must be stored online. The Catalog must be governed by same rules as rest of the database. The same query language should be used on catalog as used to query database.

Rule 5: Powerful and Well-Structured Language

One well structured language must be there to provide all manners of access to the data stored in the database. Example: SQL, etc. If the database allows access to the data without the use of this language, then that is a violation.

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Rule 6: View Updation Rule

All the view that are theoretically updatable should be updatable by the system as well.

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Rule 7: Relational Level Operation

There must be Insert, Delete, Update operations at each level of relations. Set operation like Union, Intersection and minus should also be supported.

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Rule 8: Physical Data Independence

The physical storage of data should not matter to the system. If say, some file supporting table is renamed or moved from one disk to another, it should not effect the application.

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Rule 9: Logical Data Independence

If there is change in the logical structure(table structures) of the database the user view of data should not change. Say, if a table is split into two tables, a new view should give result as the join of the two tables. This rule is most difficult to satisfy.

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Rule 10: Integrity Independence

The database should be able to enforce its own integrity rather than using other programs. Key and Check constraints, trigger etc, should be stored in Data Dictionary. This also make RDBMS independent of front-end.

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Rule 11: Distribution Independence

A database should work properly regardless of its distribution across a network. Even if a database is geographically distributed, with data stored in pieces, the end user should get an impression that it is stored at the same place. This lays the foundation of distributed database.

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Rule 12: Nonsubversion Rule

If low level access is allowed to a system it should not be able to subvert or bypass integrity rules to change the data. This can be achieved by some sort of looking or encryption

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Generalization and Specilization in ER Model

The Enhanced ER Model

As the complexity of data increased in the late 1980s, it became more and more difficult to use the traditional ER Model for database modelling. Hence some improvements or enhancements were made to the existing ER Model to make it able to handle the complex applications better.
Hence, as part of the Enhanced ER Model, along with other improvements, three new concepts were added to the existing ER Model, they were:

1. Generalization
2. Specialization
3. Aggregration

Generalization

Generalization is a bottom-up approach in which two lower level entities combine to form a higher level entity. In generalization, the higher level entity can also combine with other lower level entities to make further higher level entity.
It's more like Superclass and Subclass system, but the only difference is the approach, which is bottom-up. Hence, entities are combined to form a more generalised entity, in other words, sub-classes are combined to form a super-class.
For example, Saving and Current account types entities can be generalised and an entity with name Account can be created, which covers both.

Specialization

Specialization is opposite to Generalization. It is a top-down approach in which one higher level entity can be broken down into two lower level entity. In specialization, a higher level entity may not have any lower-level entity sets, it's possible.

Aggregration

Aggregration is a process when relation between two entities is treated as a single entity.

In the diagram above, the relationship between Center and Course together, is acting as an Entity, which is in relationship with another entity Visitor. Now in real world, if a Visitor or a Student visits a Coaching Center, he/she will never enquire about the center only or just about the course, rather he/she will ask enquire about both.

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ER Diagram MODEL

Working with ER Diagrams

ER Diagram is a visual representation of data that describes how data is related to each other. In ER Model, we disintegrate data into entities, attributes and setup relationships between entities, all this can be represented visually using the ER diagram.
For example, in the below diagram, anyone can see and understand what the diagram wants to convey: Developer develops a website, whereas a Visitor visits a website.

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ER MODEL BASIC LEVEL

 DBMS

ER Model

Entity-relationship model is a model used for design and representation of relationships between data.

The main data objects are termed as Entities, with their details defined as attributes, some of these attributes are important and are used to identity the entity, and different entities are related using relationships.
In short, to understand about the ER Model, we must understand about:

• Entity and Entity Set
• What are Attributes? And Types of Attributes.
• Keys
• Relationships

ER Model: Entity and Entity Set

Considering the above example, Student is an entity, Teacher is an entity, similarly, Class, Subject etc are also entities.
An Entity is generally a real-world object which has characteristics and holds relationships in a DBMS.
If a Student is an Entity, then the complete dataset of all the students will be the Entity Set

ER Model: Attributes

If a Student is an Entity, then student's roll no., student's name, student's age, student's gender etc will be its attributes.
An attribute can be of many types, here are different types of attributes defined in ER database model:

1. Simple attribute: The attributes with values that are atomic and cannot be broken down further are simple attributes. For example, student's age.
2. Composite attribute: A composite attribute is made up of more than one simple attribute. For example, student's address will contain, house no., street name, pincode etc.
3. Derived attribute: These are the attributes which are not present in the whole database management system, but are derived using other attributes. For example, average age of students in a class.
4. Single-valued attribute: As the name suggests, they have a single value.
5. Multi-valued attribute: And, they can have multiple values.

ER Model: Keys

If the attribute roll no. can uniquely identify a student entity, amongst all the students, then the attribute roll no. will be said to be a key.
Following are the types of Keys:

1. Super Key
2. Candidate Key
3. Primary Key

ER Model: Relationships

When an Entity is related to another Entity, they are said to have a relationship. For example, A Class Entity is related to Student entity, becasue students study in classes, hence this is a relationship.
Depending upon the number of entities involved, a degree is assigned to relationships.
For example, if 2 entities are involved, it is said to be Binary relationship, if 3 entities are involved, it is said to be Ternary relationship, and so on.

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TEXTBOOK SOLUTION LESSON 1 INVOCATION

INVOCATION 

TEXTBOOK SOLUTION

LESSON 1

INVOCATION

Translated from Atharvaveda

STANZA FOR COMPREHENSION

Let us have concord with our own people,
And concord with people who are strangers to us
Asvins, create between us and the strangers a unity of hearts.
May we unite in our minds, unite in our purposes,
and not fight against the divine spirit within us.
Let not the battle-cry rise amidst many SIain,
nor the arrows of the War-God fall with the break of the day. (M.P. 2015)

Answer these questions:

1. Who is called to create unity of hearts ?
Ans. Asvins.
2. What is the meaning of concord?
Ans. State of peaceful agreement.
3.Whose arrows will fall with the break of the day ?
Ans. War-God.
4. What does the poem inculcate?
Ans. The poem inculcates the ethics of collective living through mutual love and Understanding.
Q.5, "Divine Spirit" means.
Ans. Soul something separate from body.
0.6. "Slain" means …………
Ans. Killed in war.
0.7. Make suitable compound word with : battle, cry, war, God.
Ans. Battle-cry, War-God.
Q.8. What do you understand by "break of the day'?
Ans. Dawn, in ancient India, battles were fought between sunrise and sunset.
TEXTBOOK SOLUTION
Q.9. Who does 'us' refer to?
Ans. ‘Us' refers to the worldly people.
Q.10. What invocation is made here?
Ans. An invocation is made to unite the whole world.
Q.11. What we should create between us and strangers?
Ans. We should create a unity of hearts between strangers and us.
Q.12. Find a word in these lines which mean opposite to ‘discord’, ‘peace’.
Ans. Concord , Battle.
Q.13. What sort of unity is invocated here?
Ans. The unity of mind and purpose is invocated here.
Q.14. What should we not fight against?
Ans. We should not fight against the divine spirit within us.
Q.15. What should we not allow to rise?
Ans. We should not allow the rise of battle cry.

TEXTBOOK SOLUTION 

 

 

A. Answer the following questions in about 50-60 words: 

 

Q.1. Which are the two kinds of people referred to in the verse ?              (M.P. 2010, Imp.) 

Ans. The verse invocation inculcates the ethics of collective living through mutual love and understanding .It is an invocation made to the wordly people .there are two types of people referred to in the verse. The one are our own people these are the people with whom we have a good association .we share the same language caste and creed with them the other people are in fact the strangers who do not  belong to us they belong to different cultures and land we are required to have concord with them. 

 

Q.2. 'Let not the battle-cry rise amidst many slain' Nor the arrows of the war-god fall with the break of the day', What is implied in these lines? 

Ans. These lines say us to be far from any battle . we have already fought many battles and a lot of people have suffered in them. The battle has left many people dead with a lot of damages to the property. So, There should not be any more battle cries. The cries still haunt us. So we should not let any more cries caused by battles. 

War God Indra killed many people with his deadly arrows. His arrows never fail to kill his enemy. So, the arrows of lord(god) Indra should also stop. We should resolve all issues peacefully without hurting anybody’s feelings.  There are a lot of war victims. We have already lost a, lot of life and property.. Instead we should resolve all issues peacefully. 

 

Q.3. In how many ways is the unity sought? 

Ans. The unity is sought in more than one way. The poet calls to unite the mind of all. . We should not let any more battle-cry rise. First, we should have concord with our own people as well as with the strangers He also exports all to have a common or united purpose. He pledges all not to fight against the divine spirit that exists within all of us.  We should unite in mind and purposes. 

 

Q.4 Why does the speaker invoke the gods-Asvins?    M.P.2014 

Ans. The speaker invokes Gods – Asvins to seek for their help to bring about perfect unity between us and the strangers. Gods Asvins are the dual gods (devas) who symbolise perfect unity of the natives and the strangers. The poet here, while making invocation for unity, invokes the gods-Asvins in order to establish perfect concord and harmony between our countrymen and the foreigns. 

TEXTBOOK SOLUTION 

 

B.Answer the following questions in about 75-100 words each: 

 

Q.1. What is the message of the verse? 

Ans. Invocation' is an excerpt from Hymns from the Vedas a book of selected translations from the Vedas by Dr. Abinash Chandra Bose. In this part the ethics of collective living through mutual love and understanding have been propounded. Love and harmony are the messages which prevail throughout these verses. The verses ask for harmony and unity among our own people and strangers. Our own people are known by us on the other People who do not belong to our culture , they have different language , custom and tradition are the people strange to us , so the speaker want a peace and harmony among all the people , Difference can be resolved by love and harmony not by war.  An invocation has been made to the people to be united and live with mutual coordination not only among themselves but also with the strangers. There should be a unity in minds and purposes. We should not fight against the divine spirit within us. We should avoid wars and cries. 

Q.2. Why doeş the speaker not want the battle cry to be raised ? (M.P. 2009, 15 Imp.) 

Ans. The poet desires to establish peace in the world .Battles never resolve any problem .It only brings death. Suffering and destruction and add many more leaving a lot of unanswered questions and cries without end .It increases anger and hatred . Thus speaker does not want the battle cry to be raised. He wants the people to live unitedly and they should have concord not only among themselves but also with the people of other countries. He finds that battles are the main cause of all destruction. People suffer in huge numbers due to them battles have complicated the existing problems and have raised many new problems. It turns the life of the people into misery. The war causes wounds to humanity. Therefore the poet wants to resolve the differences in peaceful way.He wants that wars should be abolished and the peace should prevail. 

 

Q.3. How does the speaker wish to achieve concord ?               (M.P. 2012, 17 Imp.) 

Ans. This poem is an invocation for the establishment of concord in the world .The speaker is aware that people may differ in many ways yet they are similar. They have the divine spirit within them The presence of this divine spirit among all the human beings make them one. It erases the differences of native and strangers. The people of different natives religions, caste, language and custom .if there is a sense of unity among these people. It will create concord. The speaker asks for divine help to create concord. The poet says that first we should concord among our own people. We spend our life with the people of our own country. They share our joys and sorrows and stand by our side. Therefore, we must have concord with them. Then we must have concord with the strangers also. India believes in global family and pursuing the same ideal we must have proper friendship with the foreigners We should settle our disputes with them in peaceful ways. 

 

 TEXTBOOK SOLUTION 

 

 

WRITING ACTIVITY 

 

Q.A. Write a short composition on the theme, ‘Our country represents unity amid diversity’. 

India is one of the largest country of the world. It is recognized as a land of diversity. India occupies people of every caste ,different language, different religions. Its uniqueness lies in the fact that it is a federal democratic country .We have Kashmir where the temperature goes even below zero on the other hand  we have coastal region all the times hot. we equally enjoy and celebrate the festivals of Holi, ld, Christmas etc. we have so many different dresses and manners. Still we are Indian with one national song, one national anthem, one national flag, one national symbol, one judiciary and one parliament. Hence in the true sense our country represents unity amid diversity. Yet we are Indians, we are all one. 

 

 

Q.B. Every Indian takes pride in his culture and age-old traditions. Write a letter to your American friend, highlighting the salient features of Indian civilization and culture. 

Ans. 

 A-42/F, Sector 9 

DDA Flats 

Dwarka, New Delhi 

DD, MM, YY 

My dear friend, 

I was very glad to receive your letter . It gives me extreme joy to note that you wish to know about my country and you wish to visit it soon. I would like to highlight a few unique features of my country. You know India is a nation of diverse people and a land of glorious past and prosperous future. Its culture has been so rich that it had always attracted the foreigners to study. The world is still amazed at the unique culture of unity in diversity of India. It has been the land of Ram, Krishna, Gautam, Ram Krishna Paramhans and Vivekanand, Mahatma Gandhi and Subhas Chandra Bose. Every Indian feels proud to be an Indian. India can't be explained in words. So come, see and feel. It would be really an experience never before and never again. 

Yours ,

..............

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