It clears the value of the string 'tag_preamble' :p Are you curious to know, what is the function of 'tag_preamble'? Try to figure out what are the keys in the map 'attributeDB'. You can analyse, how this map is built, or you can first take a look, how it's used:

for (int i=0;i<q;i++) {
    getline(cin,inputstr); 
    if (attributeDB.find(inputstr)==attributeDB.end())
        cout << "Not Found!" << endl;
    else
        cout << attributeDB[inputstr] << endl;
}