Are there spaces between rules of the tables, how can I delete them?

Question

\documentclass[a4paper,11pt,twoside,openright]{book}

% \usepackage{geometry}
%  \geometry{
%  a4paper,
%  total={210mm,297mm},
%  left=20mm,
%  right=20mm,
%  top=20mm,
%  bottom=20mm,
%  }
\usepackage[margin=1in]{geometry}


\usepackage[utf8x]{inputenc}
\usepackage[italian]{babel}
\usepackage[T1]{fontenc}
\usepackage{fancyhdr}
\usepackage{showkeys}
% \usepackage[dvips]{graphicx}
% per le figure:
\usepackage{graphicx}
% per il testo attorno alle figure
\usepackage{floatflt,epsfig}
\usepackage{wrapfig}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage{array}
% usare colori in tabella:
\usepackage{xcolor,colortbl}
\usepackage{titlesec}
%tabelle lunghe (gestione oltre il margine)
\usepackage{longtable} 
\usepackage{ltablex}
% \usepackage{lmode rn}
% \usepackage{listings}
% \usepackage[usenames]{color}
% \usepackage{color}
% \usepackage{xcolor}
% \usepackage{xspace}
% \lstset{language=TeX,
%       backgroundcolor=\color{lightgray},
%       basicstyle=\small\ttfamily,
%       xleftmargin=3em}

\pagestyle{fancy}\addtolength{\headwidth}{20pt}
% \renewcommand{\chaptermark}[1]{\markboth{\thechapter.\#1}{}}
\renewcommand{\sectionmark}[1]{\markright{\thesection\#1}{}}
\definecolor{gray75}{gray}{0.75}
\newcommand{\hsp}{\hspace{20pt}}
\titleformat{\chapter}[hang]{\Huge\bfseries}{\thechapter\hsp\textcolor{gray75}{|}\hsp}{0pt}{\Huge\bfseries}
\cfoot{}
\rhead[\fancyplain{}{\bfseries\leftmark}]{\fancyplain{}
{\bfseries\thepage}}
\lhead[\fancyplain{}{\bfseries\thepage}]{\fancyplain{}
{\bfseries\rightmark}}

\begin{document}
\begin {flushright}
Dedica
\end {flushright}

\tableofcontents

\begin{table}[!ht]
\centering\scriptsize
\begin{tabular}{|c|m{4 cm}|m{4.5 cm}|m{3 cm}|}
\rowcolor{orange}
\rule[1ex]{0ex}{3ex}
Entità&Significato&Attributi&Identificatori \\
\midrule
Utente&
Utente finale registrato al servizio&
\begin{description}
 \item{} Username - Stringa  
 \item{} Password - Stringa 
 \item{} Nome - Stringa  
 \item{} Cognome - Stringa 
 \item{} DataNascita - Data 
 \item{}  PayPal - Stringa 
 \item{} IndirizzoDomicilio - Stringa 
\end{description}
&
Username \\

\bottomrule
\end{tabular}
\caption{Tabella Entità}
\end{table}


\end{document}

Answer 1

Yes, there are separations above and below the horizontal rules if the booktabs package is included -- this is a nice design feature of that package!

If it is really necessary: (However, this makes the use of booktabs basically useless!)

The spacings above and below a horizontal rule made by \toprule, \bottomrule, midrule and \cmidrule (all provided by booktabs package) can be controlled with the lengths

\aboverulesep and \belowrulesep. Setting them both to 0pt will cause the separation to vanish:

\setlength{\aboverulesep}{0pt}
\setlength{\belowrulesep}{0pt}

I've done this within the table environment to restrict the change to the current table, not globally.

\documentclass[a4paper,11pt,twoside,openright]{book}


\usepackage[margin=1in]{geometry}


\usepackage[utf8x]{inputenc}
\usepackage[italian]{babel}
\usepackage[T1]{fontenc}
\usepackage{fancyhdr}
\usepackage{showkeys}
\usepackage{graphicx}
% per il testo attorno alle figure
\usepackage{floatflt,epsfig}
\usepackage{wrapfig}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage{array}
% usare colori in tabella:
\usepackage{xcolor,colortbl}
\usepackage{titlesec}
%tabelle lunghe (gestione oltre il margine)
\usepackage{longtable} 
\usepackage{ltablex}

\pagestyle{fancy}\addtolength{\headwidth}{20pt}
% \renewcommand{\chaptermark}[1]{\markboth{\thechapter.\#1}{}}
\renewcommand{\sectionmark}[1]{\markright{\thesection\#1}{}}
\definecolor{gray75}{gray}{0.75}
\newcommand{\hsp}{\hspace{20pt}}
\titleformat{\chapter}[hang]{\Huge\bfseries}{\thechapter\hsp\textcolor{gray75}{|}\hsp}{0pt}{\Huge\bfseries}
\cfoot{}
\rhead[\fancyplain{}{\bfseries\leftmark}]{\fancyplain{}
{\bfseries\thepage}}
\lhead[\fancyplain{}{\bfseries\thepage}]{\fancyplain{}
{\bfseries\rightmark}}

\begin{document}
\begin {flushright}
Dedica
\end {flushright}

\tableofcontents

\begin{table}[!ht]
\setlength{\aboverulesep}{0pt}
\setlength{\belowrulesep}{0pt}
\centering\scriptsize
\begin{tabular}{|c|m{4 cm}|m{4.5 cm}|m{3 cm}|}
\rowcolor{orange}
\rule[1ex]{0ex}{3ex} %%%% Why???? Why not \toprule with other thickness?
Entità&Significato&Attributi&Identificatori \\
\midrule
Utente&
Utente finale registrato al servizio&
\begin{description}
 \item{} Username - Stringa  
 \item{} Password - Stringa 
 \item{} Nome - Stringa  
 \item{} Cognome - Stringa 
 \item{} DataNascita - Data 
 \item{}  PayPal - Stringa 
 \item{} IndirizzoDomicilio - Stringa 
\end{description}
&
Username \\

\bottomrule
\end{tabular}
\caption{Tabella Entità}
\end{table}


\end{document}