Solidity Example - record of reading

Solidity

contract proofOfBook {     

	mapping(string => uint) books;
	mapping(address => Log) logs;

    struct Log {
        string isbn;
        uint date;
        uint rate;
    }
    Log x;

    function getMyLog() returns(string x) {
        x = logs[msg.sender].isbn;
        return x;
    }

    function getCount(string isbn) returns(uint count) {
        count = books[isbn];
    }
    function logging(string isbn, uint date, uint rate) returns(bool) {         
    	logs[msg.sender] = Log(isbn, date, rate);
    	books[isbn] += 1;
    	return true;
    }
}