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zhenek [66]
3 years ago
10

Suppose we have a relation schema R(A, B, C) with FD A rightarrow B. Suppose also that we decide to decompose this schema into S

(A, B) and T(B, C). Give an example of an instance of relation R whose projection onto S and T and subsequent rejoining as in Section 3.4.1 does not yield the same relation instance. That is, pi_A, B(R) pi_B, C (R) notequalto R.

Computers and Technology
1 answer:
4vir4ik [10]3 years ago
7 0

Answer:

Check the explanation

Explanation:

A relation schema is the fundamental schema for a table. Which is In a relational kind of database (what individuals naturally refer to when they talk about database) each take can be referred to as a "relation" . therefore a relational schema is the design for the table.

kindly check the attached image below to see the step by step solution to the question.

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Given a string variable string 's;', implement a tokenizer to identify the unique tokens contained in this string, identify all
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Answer:

#include <iostream>

#include <string>

#include <vector>

#include <cctype>

#include <algorithm>

using namespace std;

void matrixInit( vector< vector<int> >& matrix, int numRows, int numCols);

struct TokenFreq{

string token;

int freq;

};

string spaces(string& istr, string& newstr);

void printVector(vector<TokenFreq> & tfVec);

void getTokenFreqVec( string& istr, vector<TokenFreq> & tfVecVec);

void selectionSort( vector<TokenFreq> & tokFreqVector );  

void insertionSort( vector<TokenFreq> & tokFreqVector );

//main

int main(int argc, const char * argv[]) {

 

vector<vector<int> > matrix;

matrixInit(matrix, 3, 4);

 

string ostr1 = " I do keep the main points straight in my head most of the time, and I do know where to find the details when I need them. by Bjarne Stroustrup";

string ostr2 = " ";

string ostr3 = "Your time is limited, so don’t waste it living someone else’s life.Stay Hungry. Stay Foolish.";

//string ostr = ostr2;

string istr;

 

cout << "Enter the text: ";

getline(cin, istr);

vector<TokenFreq> tfVec;

getTokenFreqVec(istr, tfVec);

selectionSort(tfVec);

insertionSort(tfVec);

return 0;

}

//-----

void selectionSort( vector<TokenFreq> & tokFreqVector ){

TokenFreq temp;

int min;

 

for( int i = 0; i < int(tokFreqVector.size()-1); i++){

min = i;

for (int j = i+1; j <int(tokFreqVector.size()); j++){

if (tokFreqVector[j].freq < tokFreqVector[min].freq)

min = j;

}

if(min!=i)

{

temp = tokFreqVector[i];

tokFreqVector[i] = tokFreqVector[min];

tokFreqVector[min] = temp;

}

}

cout<<"-----selectionSort------------------"<<endl;

printVector(tokFreqVector);

}

void insertionSort( vector<TokenFreq> & tokFreqVector ){

TokenFreq temp;

int max;

 

for( int i = 0; i < int(tokFreqVector.size()-1); i++){

max = i;

for (int j = i+1; j < int(tokFreqVector.size()); j++){

if (tokFreqVector[j].freq > tokFreqVector[max].freq)

max = j;

}

if(max!=i)

{

temp = tokFreqVector[i];

tokFreqVector[i] = tokFreqVector[max];

tokFreqVector[max] = temp;

}

}

cout<<"-----insertionsort------------------"<<endl;

printVector(tokFreqVector);

}

string spaces(string& istr, string & newstr){

int j;

//Check double space and create new string with lowercase

for (int i = 0; i < int(istr.length()); ++i){

istr[i] = tolower(istr[i]);

if (isspace(istr[i])){

//check double space again

j = i+1;

while(true){

if (istr[j] == '\342') istr[j]=' ';

if (istr[j] == '\200') istr[j]=' ';

if (istr[j] == '\224') istr[j]=' ';

if(isspace(istr[j])) j++;

else break;

}

i=j-1;

newstr = newstr + istr[i];

}else

newstr = newstr + istr[i];

}

return newstr;

}

void getTokenFreqVec( string& istr, vector<TokenFreq> & tfVec){

string newstr;

int curr_beg = 0;

int curr_end = 0;

string word;

bool check = false;

int index=0;

 

//call func spaces to get new string

newstr = spaces(istr, newstr);

//cout << newstr << endl;

//cout << endl;

//cout << newstr << "||" << endl;

string tempstr = newstr;

 

if(newstr != " "){

tfVec.push_back(TokenFreq());

}

for (int i = 0; i < int(newstr.length()); ++i){

if(isspace(newstr[i])){

check = false;

 

curr_end = i;

word = tempstr.substr(curr_beg, curr_end - curr_beg);

curr_beg = i + 1;

 

for (int j = 0; j < int(tfVec.size()); j++){

if (tfVec[j].token == word){

tfVec[j].freq++;

check = true;

 

break;

}

}//end-for;

if (check == false && i!=(int(newstr.length())-1)){

//cout <<"**"<< word <<"**"<<word.length()<< endl;

tfVec[index].token=word;

tfVec[index].freq=1;

index++;

tfVec.push_back(TokenFreq());

}

word = "";

//add last value

}

}//end-for

 

if(!isspace(newstr[int(newstr.length())-1])){

word = tempstr.substr(curr_beg, curr_end - (int(newstr.length())-1));

tfVec[index].token=word;

tfVec[index].freq=1;

//tfVec.push_back(TokenFreq());

}

 

printVector(tfVec);

}

void printVector(vector<TokenFreq> & tfVec){

 

cout << "size= {" << tfVec.size() << endl;

for (int i = 0; i < int(tfVec.size()); i++){

cout << " [" << i << "] = (token = \""<< tfVec[i].token <<"\", freq = " << tfVec[i].freq << ")" << endl;

//cout << tfVec[i].token<<endl;;

}

cout << endl;

}

void matrixInit( vector< vector<int> >& matrix, int numRows, int numCols){

int i;

int j;

matrix.resize(numRows, vector<int>(numCols) );

for(i = 0; i< numRows; i++ ){

for(j = 0; j < numCols; j++ )

matrix[i][j] = i*j;

}

 

cout << "size of matrix is: " << numRows << "x" << numCols << endl;

for (i = 0; i < numRows; i++){

for (j = 0; j < numCols; j++){

cout<< "matrix[" << i << "][" << i << "]=" << matrix[i][j] << endl;

}

}

cout << endl;

}

Explanation:

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