\documentclass{article}
\title{Database Connection for the CPS Facilitator Tool}
\author{Jos Kraaijeveld}
\date{\today}
\usepackage{moreverb}
\usepackage{fullpage}
\usepackage{framed}
\usepackage{float}
\usepackage{multirow}
\usepackage[final]{pdfpages}
\usepackage{hyperref}
\begin{document}

\maketitle

\pagebreak

\tableofcontents

\pagebreak

\section{Introduction}
	This document describes the database design and implementation for the CPS Facilitator Tool. The goal is to make
	sure everyone can communicate with the RDF-based database without having to write queries. The DBInterface is
	written in PHP and requires slight PHP knowledge before use. It is heavily based on initial work by Bas van Nuland. \\
		
	If you use this framework, you can skip to the `How to use'-part of this document (\ref{howtouse}). If you are
	planning to improve this framework, I recommend reading the RDF Primer\footnote{http://www.w3.org/TR/rdf-primer/} and
	SPARQL Query Language for RDF\footnote{http://www.w3.org/TR/rdf-sparql-query/}. A full specification of the current
	implementation can be found in section \ref{spec}. The areas I suggest improving upon first are described in section
	\ref{futurework}.

\section{How to use}\label{howtouse}
	\subsection{Initialization}
		Before the database can be used, you should initialize a \textit{DatabaseInterface} object. This is the only
		database class you will use. This is done calling the DatabaseInterface constructor. 
		\begin{verbatimtab}
			$db = new DatabaseInterface();
		\end{verbatimtab}

	\subsection{Basic queries}
		\subsubsection{Retrieving data}
			Getting data is done by calling the get method of the DatabaseInterface class. The specification for this
			method is as follows. \\ \\
			\begin{tabular}{| l || r |} \hline
				\multicolumn{2}{|c|}{Function get()} \\ \hline
				First argument: \$type  & String \\ \hline
				Second argument: \$arguments & Array \\ \hline
				Return type: & Array/Variable \\ \hline
			\end{tabular}  \\ \\

			The return type is an Array of objects with the type specified as the first argument. For instance, if
			the first argument is ``user", the function will return an array of User objects. The second argument can be
			left out if you want to retrieve all entries of a specific type. Below are a few examples showing the usage
			of get(). A description of what arguments are possible per type is given in section \ref{arguments}.

			\begin{figure}[H]
				\caption{Retrieving all questions and echo their title.}
				\begin{framed}
					\begin{verbatimtab}
$questions = $db->get("question");
foreach ($questions as $question)
{
	echo $question->title;
}
					\end{verbatimtab}
				\end{framed}	
			\end{figure}	

			\begin{figure}[H]
				\caption{Retrieving all surveys containing questions with IDs q1 and q2, created by the user
					Jos, printing all questions in those surveys}
				\begin{framed}
					\begin{verbatimtab}
//To get all surveys created by the user Jos, we need his UID. 
//We first query the database for the User object belonging to Jos.
$userResults = $db->get("user", array("name" => "Jos"));
//Assuming there is a result, the UID is:
$josUID = $userResults[0]->uid;
//Now to get the requested surveys:
$surveys = $db->get("survey", array("questions" => array("q1", "q2"),
			            "creator" => $josUID));
//And to print all the questions in these surveys:
foreach($surveys as $survey)
{
	echo "All the questions in " . $survey->name;
	foreach($survey->questions as $question)
	{
		print_r($question);
	}
}
					\end{verbatimtab}
				\end{framed}
			\end{figure}	

		\subsubsection{Storing data}
			Storing data is easy, as long as you stick to using the given PHP Classes. Retrieve these classes by using
			the get() function, and pass them as a parameter to the set() function of the DatabaseInterface. This set()
			function will determine what type the object is and store it at the correct location. The method overview is
			as follows: \\ \\
			\begin{tabular}{| l || r |} \hline
				\multicolumn{2}{|c|}{Function set()} \\ \hline
				First argument: \$rToolObject  & Variable \\ \hline
			\end{tabular}  \\ \\
			
			Another important thing to note is that currently it will overwrite a previous object with the same UID in
			the database. The following examples show how to create new objects and save them, as well as edit old
			objects and save them.

			\begin{figure}[H]
				\caption{Creating a new Answer object and storing this in the database.}
				\begin{framed}
					\begin{verbatimtab}
//For this example, I choose a random question to answer					
$questions = $db->get("question");
$question = $questions[2];
//Note two things:
//1 - If you pass 'null' as first argument when creating any object
// 	  A new UID will be generated, indicating a new object.
//2 - Depending on the question, there can be multiple answers
//	  This means the values-argument (third argument) is an array.
$answer = new Answer(null, $question, array("12345", "four"));
//Save the answer in the database
$db->set($answer);
					\end{verbatimtab}
				\end{framed}	
			\end{figure}	

			\begin{figure}[H]
				\caption{Getting a Survey object from the database and removing the first question. Also alter this
					question.}
				\begin{framed}
					\begin{verbatimtab}
//Get the survey
$surveyResults = $db->get("survey", array("uid" => "b91d39e8667372e220bb861b3f94b5bd"));				
$survey = surveyResults[0];
//Remove the question
$question = $survey->questions[0];
unset($survey->questions[0]);
//Change the question
$question->title = "New Title";
//Save the survey and question
$db->batchSet(array($survey, $question));
					\end{verbatimtab}
				\end{framed}
			\end{figure}


	\subsection{Arguments}\label{arguments}	
		The arguments you can supply when calling the get() function differ greatly per type. Unfortunately, there is no
		way around this, so here is a complete overview of arguments per type. \\
		\begin{tabular}{| l | c | c | l |} \hline
			\textbf{Type} 					& \textbf{Argument name} 	& \textbf{Argument type} 	& \textbf{Extra notes}  \\ \hline \hline
			\multirow{3}{*}{Answer}			& uid						& String					&						\\
											& question					& String					& UID of the question	\\
											& values					& Array of Strings			& 						\\ \hline \hline
			\multirow{4}{*}{AnswerSet}		& uid						& String					& 						\\
											& survey					& String					& UID of the Survey		\\
											& respondent				& String					& UID of the Respondent	\\
											& answers					& Array of Strings			& UIDs of the Answers   \\ \hline \hline
			\multirow{4}{*}{Application}	& uid						& String					& \\
											& title						& String					& \\
											& description				& String					& \\
											& style						& String					& \\ \hline \hline
			\multirow{5}{*}{Question}		& code						& String					& \\
											& title						& String					& \\
											& type						& String					& \\
											& description				& String					& \\
											& category					& String					& \\
											& definedanswers					& Array of Strings			& String values of possible answers \\ \hline \hline
			\multirow{3}{*}{Respondent/User}& uid						& String					& \\
											& name						& String					& \\
											& password					& String					& Use hashes to store passwords \\ \hline \hline
			\multirow{6}{*}{Session}		& uid						& String					& \\
											& title						& String					& \\
											& creator					& String					& UID of the User \\
											& datetime					& String					& Unix Timestamp. No way to search on intervals (yet). \\
											& applications				& Array of Strings			& UIDs of the Applications \\
											& surveys					& Array of Strings			& UIDs of the Surveys \\
											& answersets				& Array of Strings			& UIDs of the AnswerSets \\ \hline \hline
			\multirow{4}{*}{Survey}			& uid						& String					& \\
											& title						& String					& \\
											& description				& String					& \\
											& creator					& String					& UID of the user that created this survey \\
											& questions					& Array of Strings			& UIDs of the Questions \\ \hline \hline
		\end{tabular} \\

		Whenever an Array has to be supplied, it will match for results that satisfy \textit{all} the constraints given
		in the array. 
			
\section{Specification}\label{spec}
	\subsection{Models}
		The framework heavily relies on the Object Oriented Programming paradigm, and only allows you to create, edit
		and store data through instances of precreated classes. All these classes inherit from a global
		ResearchToolObject class. A UML class diagram of the model classes can be found in Appendix \ref{models}.  
	\subsection{Connectors}
		Although the front end developer only uses one general DatabaseInterface, the different files for the different
		datatypes are accessed by seperate connectors. A connector has to implement the IConnector interface, which
		mainly enforces the get() and set() methods to ensure a connector can perform as expected. The rest of the
		methods are implemented in the baseclass Connector, which should be extended. In every connector,
		the get() and set() methods are different. A get() method builds the querystring based on the given arguments,
		then retrieves the data and performs other necessary queries (like retrieving a different object from another
		file) to ensure the PHP DataModel is comoplete. A set() method has to store the data accordingly. 
	\subsection{PHPDoc}	
		PHPDoc for the database classes can be found at
		\href{http://svn.tbm.tudelft.nl/TBM-CPS/RESEARCHTOOL/Doc/Backend/PHPDoc/index.html}{SVN}.

\section{Future Work}\label{futurework}
	\subsection{Adhere to Open-Closed Principle}
		At the moment, \textit{the DatabaseInterface.php} class violates the Open-Closed principle. Every new connector,
		four lines need to be added in this class. This is unwanted if new RDF datatypes are added. The same holds for
		the method createArguments in this class: extra cases have to be added if more types of arguments become possible.
		Adhering to the Open-Closed principle will allow for easier extention and maintenance of the database-related classes.

	\subsection{Deal with invalid or missing values}
		This goes in two parts. Firstly, the database now assumes that given an entry, all the fields for its type are there and
		filled in. This is unwanted since it can cause issues with backwards compatability of certain .rdf files. Secondly, it
		assumes that fields containing a UID to a different entry actually point to a valid entry. For instance, a Survey query will
		try to get a User object as its creator value from the database as well, assuming it exists. It will break if this user object
		does not exist.

\appendix
\pagebreak
\section{Class diagram of the models}\label{models}
	\begin{figure}
		\includepdf[scale=1.22]{DBModels.pdf}
	\end{figure}	

\end{document}
