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A recursive relationship is a relationship among entities of the same class, and is represented in the same way as other relationships are. The rows of the tables can take two different roles, however. Some are parent rows, and others are child rows. Further, the table will contain both its own primary key and the foreign key that links back to the table itself. If a row has no parent, then the value of the foreign key column in that row will be null. If the row has a parent, then there must be a foreign key value in that row that corresponds to the primary key value of another row in the table.

A recursive relationship is a relationship between an entity and itself. 

For example, given the entity PERSON, a recursive relationship could be used to show a PERSON and his or her SIBLINGs (brothers and sisters).

The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.

It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.

The advantages of stored procedures are 

(1) greater security, 

(2) decreased network traffic, 

(3) the fact that SQL can be optimized and 

(4) code sharing which leads to less work, standardized processing, and specialization among developers.

The steps are: 

(1) specify the primary key, 

(2) specify candidate keys, 

(3) specify column properties including null status, data type, default value (if any), and data constraints (if any), and 

(4) verifying normalization.

Data constraints on a column are the limits put on the values the data can have. 

There are four types of data constraints: 

(1) domain constraints, which define a limited set of values for the column, 

(2) range constraints, which specify that the values must fall within a certain range, 

(3) intrarelation constraints, which define what values the column can have based on values of other columns in the same table, and 

(4) interrelation constraints, which define values the column can have based on values of columns in other tables.

You communicate with an RDBMS using Structured Query Language (SQL).

SQL statements return a set of rows, while an application program works on one row at a time. To resolve this mismatch the results of SQL statements are processed as pseudofiles, using a cursor or pointer to specify which row is being processed.

Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic.

The ideal primary key is short, numeric and fixed. A surrogate key is a unique, DBMS-supplied identifier intended to be used as the primary key of a table. Further, the DBMS will not allow the value of a surrogate key to be changed. The values of a surrogate key have no meaning to the users and are usually hidden on forms and reports. By design, they are short, numeric and fixed and thus meet the definition of the ideal primary key

An ACID transaction is one that is atomic, consistent, isolated, and durable. Durable means that database changes are permanent. Consistency can mean either statement level or transaction level consistency. With transaction level consistency, a transaction may not see its own changes. There are four transaction isolation levels: read committed, read uncommitted, repeatable read and serialization. Atomic means it is performed as a unit.

SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.

A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted. For any one table, there are twelve events for which you can define database triggers. A database trigger can call database procedures that are also written in PL/SQL.

There are three (3) ways to create an Oracle database. You can create a database using the Database Configuration Assistant, using the Oracle-supplied database creation procedures or using the SQL CREATE DATABASE command.

There are three major sets of files on disk that compose a database. 

All the files are binary. These are 

1. Database files 

2. Control files 

3. Redo logs

The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself. All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.

A sequence is an object that generates a sequential series of unique numbers. Sequences are most often used to provide values for surrogate keys. However, there are three problems with using sequences. First, a developer can use a defined sequence for any purpose; and if a sequence is used for purposes other than the surrogate key, some values will be missing. A second problem is that there is nothing in the schema that prevents someone from issuing an INSERT statement that adds data to the table but that does not use the sequence. Finally, it is possible to use the wrong sequence when putting data into a table.

Indexes can be created to enforce uniqueness, to facilitate sorting, and to enable fast retrieval by column values. A good candidate for an index is a column that is frequently used with equal conditions in WHERE clauses.

Datafiles, control files and two types of ReDo log files: OnLine Redo and Offline ReDo (which is also known as Archive ReDo).

Choosing primary and secondary keys can increase the speed of row selection, joining, and row ordering. Selecting the appropriate file organization for base tables and indexes can also improve performance. Clustering related rows together and maintaining statistics about tables and indexes can lead to increased efficiency.

Due to the high compressibility of gases, it is possible to compress large volumes of gases in small cylinders & transport them easily.

Lichens and Mosses (a) and (b). Lichens and mosses release substances which break down the stones resulting in the formation of soil.

Energy stored = 1/2 × F × x   .......(1)                      

also in terms of spring constant                                         

 F = k ∙ x                      

hence                                          

x = (F/k)                      

hence from (1),                      

Energy = (1/2) × F × (F/k) = (F² / 2k)                      

Here F = Tension in the spring                      

hence F = T                               

 ∴ Energy = [T² / 2k]   

Data definition language commands are used to create, alter, and drop tables. Data manipulation commands are used to insert, modify, update, and query data in the database. Data control language commands help the DBA to control the database.

1. Identify the data type, length, and precision for each attribute. 

2. Identify the columns that can accept a null value. 

3. Identify the columns that need to be unique. 

4. Identify primary and related foreign keys with the parent table being created before the child. 

5. Determine default values. 

6. Determine where the domain values are that need to be constrained. 

7. Create the indexes.

As the tangents to the curve y = x³ - 3x² - 9x + 7 are parallel to x-axis so, 

dy/dx = 3x² - 6x - 9 = 0 

3(x² - 2x - 3) = 0

x = 3,-1

Hence the required points are (3, -20) and (-1,12). 

A hand cultivator is a gardening tool that is used to turn the soil where you plan on planting and for removing weeds. In small flower or vegetable gardens, it can also be used like a small plow to dig the planting rows.

The overlapping significance signify the social difference in one sphere overlapping across the another sphere. It is demonstrated by the poor economic condition of socially depressed communities. In such a situation, the social and economic conditions of the community may be used to be overlapping each other.

Difference between seepage, infiltration and percolation :

Seepage - When water enters the ground surface at the upstream side of a retaining structure like a dam and comes out at the downstream side.

Infiltration - When water enters the ground surface but doesn't come out, thus increasing the moisture content of the soil.

Percolation - When water enters the ground surface and travels through the soil to finally join the ground water reserves.

It is necessary to break the crumb(puddling) after ploughing because Puddler is used for preparation of paddy fields with standing water after initial ploughing. It breaks up the clods and churns the soil. The main purpose of puddling is to reduce percolation of water, to kill weeds by decomposing and to facilitate the transplanting of paddy seedlings by making the soil softer.

The steps involved in puddling are: 

1. saturating and flooding the soil. 

2. plowing the supersaturated soil; 

3. plowing or harrowing at progressively lower water contents.

Advantages of Puddling:

(i) Less power is required for tillage. 

(ii) Puddling hastens transplanting operation easily and smoothly as well as the establishment of seedlings. 

(iii) Puddling creates an impervious layer below the surface to reduce deep percolation of water and to provide soft seed bed for planting paddy, wheat, onion etc. Puddling increases the moisture retention capacity of a soil. 

(iv) Puddling is an important method of controlling some weeds such as Cynodon dactylon, Cyperus rotundus etc.

https://www.sarthaks.com/565519/letter-selected-random-from-english-alphabet-the-probability-of-it-being-roman-number-is

In English language there are 26 alphabets.

The roman numbers in alphabets are I, V, X, L, C, D and M

The probability of roman number in English alphabet = 7/26

Let the final temperature reached be t℃

Specific heat capacity of water = c = 1000 J kg⁻ ℃⁻

Given masses = 1 kg and 2 kg

Respective temperatures = 30℃ and 0℃

By zeroth law of Thermodynamics,

Heat lost by 0℃ water = Heat gained by 0℃ water

i.e. 1 × c × (30-t) = 2 × c ×(t-0)

 30 - t = 2t

30 = 3t

t = 10

Change in entropy of 30℃ water = {1×1000×(10–0)}/(10+273)

= 35.33 j/k

Change in entropy of the 0℃ water = -{(2×1000×(30–10)}/(10+273)

= 212.01 j/k

However the net change in the entropy of the total system(of 30℃ water and 0℃ water) 

= 35.33 - 212.01 j/k

 = 176.88 j/k

The production of genetically modified (GM) or transgenic plants has several advantages.

• Most of the GM crops have been developed for pest resistance, which increases the crop productivity and therefore, reduces the reliance on chemical pesticides.
•  Many varieties of GM food crops have been developed, which have enhanced nutritional quality. For example, golden rice is a transgenic variety in rice, which is rich in vitamin A.
•  These plants prevent the loss of fertility of soil by increasing the efficiency of mineral usage.
• They are highly tolerant to unfavourable abiotic conditions.
•  The use of GM crops decreases the post harvesting loss of crops.

However, there are certain controversies regarding the use of genetically modified crops around the world. The use of these crops can affect the native biodiversity in an area. For example, the use of Bt toxin to decrease the amount of pesticide is posing a threat for beneficial insect pollinators such as honey bee. If the gene expressed for Bt toxin gets expressed in the pollen, then the honey bee might be affected. As a result, the process of pollination by honey bees would be affected. Also, genetically modified crops are affecting human health. They supply allergens and certain antibiotic resistance markers in the body. Also, they can cause genetic pollution in the wild relatives of the crop plants. Hence, it is affecting our natural environment.

Clearly here C divides AB in 2 : 1

so, position vector of C = (2 vector(b + a))/3).

Price elasticity of demand (PED) shows the relationship between price and quantity demanded and provides a precise calculation of the effect of a change in price on quantity demanded.

A standard language can hinder the effort to create a new language. One standard is never enough to meet all of the business needs. A standard can be a compromise among interested parties which can cause the standard to not be ideal. If a standard is altered by some, than portability between platforms could be hurt.

A join allows tables to be linked to other tables when a relationship between the tables exists. The relationships are established by using a common column in the tables and often uses the primary/foreign key relationship.