report: add ideas on three kinds of applications

doc/report/applications.tex

@@ -4,6 +4,32 @@ With endpoints in place, we can now query the ULO/RDF
 data set. Depending on the kind of application, different interfaces
 and approaches to querying the database might make sense.
 
+\subsection{Kinds of Applications}
+
+Storing information in RDF triplets allows for any kind of queries,
+meaning it is not optimized for any kind of application. For the sake
+of this project, we tried out three categories of applications.
+
+\begin{itemize}
+    \item Of course the initial starting point for this project was
+      the idea of tetrapodal search. Our first application
+      \emph{ulosearch} tires to offer an easy way of searching in the
+      ULO/RDF data set.
+
+    \item With lots of data in a database, it appears attractive to
+      visualize the data set in some kind graphical way in the
+      \emph{ulovisualize} application.
+
+    \item Finally, we want to experiment a bit. The available ULO/RDF
+      data sets are about proofs and theorems and should include links
+      between. It might be interesting to find out which proofs and
+      definitions are more important than others such that we can
+      create a kind of ranking of them. This is explored in the
+      \emph{ulorate} application.
+\end{itemize}
+
+\subsection{Database Interface}
+
 For integrating the ULO/RDF data set into an existing application, it
 probably is reasonable to directly query the data set using RDF4J.
 That is, of course, assuming the existing co debase is based on the