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diff --git a/doc/report/figs/screenshot1.png b/doc/report/figs/screenshot1.png
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diff --git a/doc/report/implementation-screenshots.tex b/doc/report/implementation-screenshots.tex
new file mode 100644
index 0000000000000000000000000000000000000000..1776c3fd2494c4b6ececce78758ad80bb73eb912
--- /dev/null
+++ b/doc/report/implementation-screenshots.tex
@@ -0,0 +1,22 @@
+\begin{figure}
+ \centering
+ \begin{subfigure}[b]{0.8\textwidth}
+ \centering
+ \shadowbox{\includegraphics[width=\textwidth]{figs/screenshot0.png}}
+ \caption{Scheduling a new import job in the web interface.}
+ \end{subfigure}
+ \vspace{5mm}
+
+ \begin{subfigure}[b]{0.8\textwidth}
+ \centering
+ \shadowbox{\includegraphics[width=\textwidth]{figs/screenshot1.png}}
+ \caption{Reviewing a previous import job. This particular job
+ failed, which illustrates how our web interface presents errors
+ and logs.}
+ \end{subfigure}
+ \caption{The web interface for controlling the Collector and
+ Importer components. While Collector and Importer can also be
+ used as library code or with a command line utility, managing
+ jobs in a web interface is probably the most
+ convenient.}\label{fig:ss}
+\end{figure}
diff --git a/doc/report/implementation-transitive-closure.tex b/doc/report/implementation-transitive-closure.tex
index 0898943116f4456250bf8c7bbf2ebd692bb4bc03..6be0206a892a98fa32f3e038e67c53b91ee09603 100644
--- a/doc/report/implementation-transitive-closure.tex
+++ b/doc/report/implementation-transitive-closure.tex
@@ -6,14 +6,15 @@
\caption{We can think of this tree as visualizing a relation~$R$ where
$(X, Y)~\in~R$ iff there is an edge from~$X$ to~$Y$.}
\end{subfigure}
+ \hspace{5mm}
\begin{subfigure}[b]{0.4\textwidth}
\centering
\includegraphics[width=\textwidth]{figs/tree-transitive.pdf}
\caption{Transitive closure~$S$ of relation~$R$. Additionally to
each tuple from~$R$ (solid edges), $S$~also contains additional
- transitive edges (dotted lines).}
+ transitive edges (dotted edges).}
\end{subfigure}
- \caption{Illustrating the idea behind the transative closure. A
- transative closure~$S$ of relation~$R$ is defined as the
+ \caption{Illustrating the idea behind transitive closures. A
+ transitive closure~$S$ of relation~$R$ is defined as the
``minimal transitive relation that contains~$R$''~\cite{tc}.}\label{fig:tc}
\end{figure*}
diff --git a/doc/report/implementation.tex b/doc/report/implementation.tex
index a57d010894d113b3ecac0470b3ad42d47770e80a..10f1094151c952e09551852ba08bbf0b394657d0 100644
--- a/doc/report/implementation.tex
+++ b/doc/report/implementation.tex
@@ -12,9 +12,9 @@ describes some details of the actual implementation for this project.
With RDF files exported and available for download as Git
repositories~\cite{uloisabelle, ulocoq}, we have the goal of making
the underlying data available for use in applications. Let us first
-look at a high level overview of all involved
-components. Figure~\ref{fig:components} illustrates each component and
-the flow of data.
+take a high level look at the three components we made out for this
+job. Figure~\ref{fig:components} illustrates how data flows through
+the different components.
\begin{figure}[]\begin{center}
\includegraphics[width=0.9\textwidth]{figs/components.png}
@@ -37,12 +37,12 @@ the flow of data.
\emph{Endpoint} is where applications access the underlying
knowledge base. This does not necessarily need to be any custom
software, rather the programming interface of the underlying
- database itself can be understood as an endpoint of its own.
+ database server itself can be understood as an endpoint of its own.
\end{itemize}
-Collector, Importer and Endpoint provide us with an easy and automated
-way of making RDF files available for use within applications. We will
-now take a look at the actual implementation created for
+Collector, Importer and Endpoint provide us with an automated way of
+making RDF files available for use within applications. We will now
+take a look at the actual implementation created for
\emph{ulo-storage}, beginning with the implementation of Collector and
Importer.
@@ -50,21 +50,20 @@ Importer.
We previously described Collector and Importer as two distinct
components. The Collector pulls RDF data from various sources as an
-input and outputs a stream of standardized RDF data. Then, the
-Importer takes such a stream of RDF data and then dumps it to some
-sort of persistent storage. In the implementation for
-\emph{ulo-storage}, both Collector and Importer ended up being one
-piece of monolithic software. This does not need to be the case but
-proved convenient because (1)~combining Collector and Importer forgoes
-the needs for an additional IPC~mechanism and (2)~neither Collector
-nor Importer are terribly large pieces of software in themselves.
+input and outputs a stream of standardized RDF data. The Importer
+takes such a stream of RDF data and then dumps it to some sort of
+persistent storage. In our implementation, both Collector and
+Importer ended up as one piece of monolithic software. This does not
+need to be the case but proved convenient because combining Collector
+and Importer forgoes the needs for an additional IPC~mechanism
+between Collector and Importer.
Our implementation supports two sources for RDF files, namely Git
repositories and the local file system. The file system Collector
crawls a given directory on the local machine and looks for
RDF~XMl~files~\cite{rdfxml} while the Git Collector first clones a Git
repository and then passes the checked out working copy to the file
-system Collector. Because it is not uncommon for RDF files to be
+system Collector. Because we found that is not uncommon for RDF files to be
compressed, our Collector supports on the fly extraction of
gzip~\cite{gzip} and xz~\cite{xz} formats which can greatly reduce the
required disk space in the collection step.
@@ -72,7 +71,7 @@ required disk space in the collection step.
During development of the Collector, we found that existing exports
from third party mathematical libraries contain RDF syntax errors
which were not discovered previously. In particular, both Isabelle and
-Coq export contained URIs which do not fit the official syntax
+Coq exports contained URIs which do not fit the official syntax
specification~\cite{rfc3986} as they contained illegal
characters. Previous work~\cite{ulo} that processed Coq and Isabelle
exports used database software such as Virtuoso Open
@@ -95,17 +94,24 @@ into the database. As such the import itself is straight-forward, our
software only needs to upload the RDF file stream as-is to an HTTP
endpoint provided by our GraphDB instance.
+To review, our combination of Collector and Importer fetches XML~files
+from Git repositories, applies on the fly decompression and fixes and
+then imports the collected RDF~triplets into persistent database
+storage.
-\subsection{Scheduling and Version Management}
+\subsubsection{Scheduling}
Collector and Importer were implemented as library code that can be
called from various front ends. For this project, we provide both a
command line interface as well as a graphical web front end. While the
command line interface is only useful for manually starting single
-jobs, the web interface allows scheduling of jobs. In particular, it
-allows the user to automate import jobs. For example, it is possible
-to schedule an import of a given Git repository every seven days to a
-given GraphDB instance.
+jobs, the web interface allows scheduling of jobs. Import jobs can be
+started manually or scheduled automatically in a web interface
+(Figure~\ref{fig:ss}) which also keeps history and logs.
+
+\input{implementation-screenshots.tex}
+
+\subsubsection{Version Management}
Automated job control that regularly imports data from the same
sources leads us to the problem of versioning. In our current design,
@@ -122,16 +128,17 @@ representation~$\mathcal{D}$. We see that data flows
from $n$~individual libraries~$\mathcal{L}_i$ into a single
database storage~$\mathcal{D}$ that is used for querying.
-However, mathematical knowledge isn't static. When a given
-library~$\mathcal{L}^{t}_i$ at revision~$t$ gets updated to a new
-version~$\mathcal{L}^{t+1}_i$, this change will eventually propagate
-to the associated export and result in a new set of RDF
-triplets~$\mathcal{E}^{t+1}_i$. Our global database
-state~$\mathcal{D}$ needs to get updated to match the changes
-between~$\mathcal{E}^{t}_i$ and $\mathcal{E}^{t+1}_i$. Finding an
-efficient implementation for this problem is not trivial. While it
-should be possible to find out the difference between two
-exports~$\mathcal{E}^{t}_i$ and $\mathcal{E}^{t+1}_i$ and compute the
+However, we must not ignore that mathematical knowledge is ever
+changing and not static. When a given library~$\mathcal{L}^{t}_i$ at
+revision~$t$ gets updated to a new version~$\mathcal{L}^{t+1}_i$, this
+change will eventually propagate to the associated export and result
+in a new set of RDF triplets~$\mathcal{E}^{t+1}_i$. Our global
+database state~$\mathcal{D}$ needs to get updated to match the changes
+between~$\mathcal{E}^{t}_i$ and $\mathcal{E}^{t+1}_i$.
+
+Finding an efficient implementation for this problem is not trivial.
+While it should be possible to compute the difference between two
+exports~$\mathcal{E}^{t}_i$ and $\mathcal{E}^{t+1}_i$ and infer the
changes necessary to be applied to~$\mathcal{D}$, the big number of
triplets makes this appear unfeasible. As this is a problem an
implementer of a greater tetrapodal search system will encounter, we
@@ -142,7 +149,7 @@ versioning information about which particular
export~$\mathcal{E}^{t}_i$ it was derived from. During an import
from~$\mathcal{E}^{s}_i$ into~$\mathcal{D}$, we could (1)~first remove all
triplets in~$\mathcal{D}$ that were derived from the previous version
-of~$\mathcal{E}^{t-1}_i$ and (2)~then re-import all triplets from the current
+of~$\mathcal{E}^{s-1}_i$ and (2)~then re-import all triplets from the current
version~$\mathcal{E}^{s}_i$. Annotating triplets with versioning
information is an approach that should work, but it does
introduce~$\mathcal{O}(n)$ additional triplets in~$\mathcal{D}$ where
@@ -152,29 +159,33 @@ solution.
Another approach is to regularly re-create the full data
set~$\mathcal{D}$ from scratch, say every seven days. This circumvents
-all problems related to updating existing data sets, but it does have
-additional computation requirements. It also means that changes in a
-given library~$\mathcal{L}_i$ take some to propagate to~$\mathcal{D}$.
-Building on top of this idea, an advanced version of this approach
-could forgo the requirement of only one single database
-storage~$\mathcal{D}$. Instead of only maintaining one global database
-state~$\mathcal{D}$, we suggest the use of dedicated database
-instances~$\mathcal{D}_i$ for each given library~$\mathcal{L}_i$. The
-advantage here is that re-creating a given database
-representation~$\mathcal{D}_i$ is fast as exports~$\mathcal{E}_i$ are
-comparably small. The disadvantage is that we still want to query the
-whole data set~$\mathcal{D} = \mathcal{D}_1 \cup \mathcal{D}_2 \cup
-\cdots \cup \mathcal{D}_n$. This requires the development of some
-cross-repository query mechanism, something GraphDB currently only
-offers limited support for~\cite{graphdbnested}.
+the problems related to updating existing data sets, but also means
+that changes in a given library~$\mathcal{L}_i$ take some to propagate
+to~$\mathcal{D}$. Building on top of this idea, an advanced version
+of this approach could forgo the requirement of only one single
+database storage~$\mathcal{D}$ entirely. Instead of only maintaining
+one global database state~$\mathcal{D}$, we suggest the use of
+dedicated database instances~$\mathcal{D}_i$ for each given
+library~$\mathcal{L}_i$. The advantage here is that re-creating a
+given database representation~$\mathcal{D}_i$ is fast as
+exports~$\mathcal{E}_i$ are comparably small. The disadvantage is that
+we still want to query the whole data set~$\mathcal{D} = \mathcal{D}_1
+\cup \mathcal{D}_2 \cup \cdots \cup \mathcal{D}_n$. This requires the
+development of some cross-repository query mechanism, something
+GraphDB currently only offers limited support
+for~\cite{graphdbnested}.
+
+In summary, we see that versioning is a potential challenge for a
+greater tetrapodal search system. While not a pressing issue for
+\emph{ulo-storage} now, we consider this a topic of future research.
\subsection{Endpoint}\label{sec:endpoints}
Finally, we need to discuss how \emph{ulo-storage} realizes the
Endpoint. Recall that the Endpoint provides the programming interface
-for systems that wish to query our collection of organizational
+for applications that wish to query our collection of organizational
knowledge. In practice, the choice of Endpoint programming interface
-is determined by the choice backing database storage.
+is determined by the choice of what database system to use.
In our project, organizational knowledge is formulated as
RDF~triplets. The canonical choice for us is to use a triple store,
@@ -185,47 +196,47 @@ at~\cite{graphdbfree}.
\subsubsection{Transitive Queries}
-A big advantage of GraphDB compared to other systems, such as Virtuoso
-Open Source~\cite{wikivirtuoso} used in previous work related to the
-upper level ontology~\cite{ulo}, is that it supports recent versions
-of SPARQL~\cite{graphdbsparql} and OWL~Reasoning~\cite{owlspec,
-graphdbreason}. In particular, this means that GraphDB offers
-support for transitive queries as described in previous
-work~\cite{ulo}. A transitive query is one that, given a relation~$R$,
-asks for the transitive closure~$S$ of~$R$~\cite{tc}
+A notable advantage of GraphDB compared to other systems such as
+Virtuoso Open Source~\cite{wikivirtuoso, ulo} is that GraphDB supports
+recent versions of the SPARQL query language~\cite{graphdbsparql} and
+OWL~Reasoning~\cite{owlspec, graphdbreason}. In particular, this
+means that GraphDB offers support for transitive queries as described
+in previous work~\cite{ulo}. A transitive query is one that, given a
+relation~$R$, asks for the transitive closure~$S$ of~$R$~\cite{tc}
(Figure~\ref{fig:tc}).
+\input{implementation-transitive-closure.tex}
+
In fact, GraphDB supports two approaches for realizing transitive
queries. On one hand, GraphDB supports the
-\texttt{owl:TransitiveProperty} property that defines a given
-predicate~$P$ to be transitive. With $P$~marked in this way, querying
-the knowledge base is equivalent to querying the transitive closure
-of~$P$. This, of course, requires transitivity to be hard-coded into
-the knowledge base. If we only wish to query the transitive closure
-for a given query, we can take advantage of property
-paths~\cite{paths} which allows us to indicate that a given
+\texttt{owl:TransitiveProperty}~\cite[Section 4.4.1]{owlspec} property
+that defines a given predicate~$P$ to be transitive. With $P$~marked
+in this way, querying the knowledge base is equivalent to querying the
+transitive closure of~$P$. This, of course, requires transitivity to
+be hard-coded into the knowledge base. If we only wish to query the
+transitive closure for a given query, we can take advantage of
+property paths~\cite{paths} which allows us to indicate that a given
predicate~$P$ is to be understood as transitive when querying. Only
-during querying is the transitive closure then evaluated.
+during querying is the transitive closure then evaluated. Either way,
+GraphDB supports transitive queries without awkward workarounds
+necessary in other systems~\cite{ulo}.
-\input{implementation-transitive-closure.tex}
+\subsubsection{SPARQL Endpoint}
There are multiple approaches to querying the GraphDB triple store,
one based around the standardized SPARQL query language and the other
on the RDF4J Java library. Both approaches have unique advantages.
-
-\subsubsection{SPARQL Endpoint}
-
-SPARQL is a standardized query language for RDF triplet
-data~\cite{sparql}. The specification includes not just syntax and
-semantics of the language itself, but also a standardized REST
-interface~\cite{rest} for querying database servers.
-
-\noindent\textbf{Syntax} SPARQL is inspired by SQL and as such the
-\texttt{SELECT} \texttt{WHERE} syntax should be familiar to many
-software developers. A simple query that returns all triplets in the
-store looks like
+Let us first take a look at {SPARQL}, which is a standardized query
+language for RDF triplet data~\cite{sparql}. The specification
+includes not just syntax and semantics of the language itself, but
+also a standardized REST interface~\cite{rest} for querying database
+servers.
+
+SPARQL was inspired by SQL and as such the \texttt{SELECT}
+\texttt{WHERE} syntax should be familiar to many software developers.
+A simple query that returns all triplets in the store looks like
\begin{lstlisting}
-SELECT * WHERE { ?s ?p ?o }
+ SELECT * WHERE { ?s ?p ?o }
\end{lstlisting}
where \texttt{?s}, \texttt{?p} and \texttt{?o} are query
variables. The result of any query are valid substitutions for the
@@ -233,50 +244,49 @@ query variables. In this particular case, the database would return a
table of all triplets in the store sorted by subject~\texttt{?o},
predicate~\texttt{?p} and object~\texttt{?o}.
-\noindent\textbf{Advantage} Probably the biggest advantage is that SPARQL
-is ubiquitous. As it is the de facto standard for querying
-triple stores, lots of implementations and documentation are
+Probably the biggest advantage is that SPARQL is ubiquitous. As it is
+the de facto standard for querying triple stores, lots of
+implementations (client and server) as well as documentation are
available~\cite{sparqlbook, sparqlimpls, gosparql}.
\subsubsection{RDF4J Endpoint}
-RDF4J is a Java API for interacting with triple stores, implemented
-based on a superset of the {SPARQL} REST interface~\cite{rdf4j}.
-GraphDB is one of the database servers that supports RDF4J, in fact it
-is the recommended way of interacting with GraphDB
-repositories~\cite{graphdbapi}.
+SPARQL is one way of accessing a triple store database. Another
+approach is RDF4J, a Java API for interacting with RDF graphs,
+implemented based on a superset of the {SPARQL} REST
+interface~\cite{rdf4j}. GraphDB is one of the database servers that
+supports RDF4J, in fact it is the recommended way of interacting with
+GraphDB repositories~\cite{graphdbapi}.
-\noindent\textbf{Syntax} Instead of formulating textual queries, RDF4J allows
-developers to query a repository by calling Java API methods. Previous
-query that requests all triplets in the store looks like
+Instead of formulating textual queries, RDF4J allows developers to
+query a knowledge base by calling Java library methods. Previous query
+that asks for all triplets in the store looks like
\begin{lstlisting}
-connection.getStatements(null, null, null);
+ connection.getStatements(null, null, null);
\end{lstlisting}
in RDF4J. \texttt{getStatements(s, p, o)} returns all triplets that
have matching subject~\texttt{s}, predicate~\texttt{p} and
object~\texttt{o}. Any argument that is \texttt{null} can be replace
-with any value, i.e.\ it is a query variable to be filled by the call
-to \texttt{getStatements}.
-
-\noindent\textbf{Advantage} Using RDF4J does introduce a dependency on the JVM
-and its languages. But in practice, we found RDF4J to be quite
-convenient, especially for simple queries, as it allows us to
-formulate everything in a single programming language rather than
-mixing programming language with awkward query strings.
-
-We also found it quite helpful to generate Java classes from
-OWL~ontologies that contain all definitions of the
-ontology~\cite{rdf4jgen}. This provides us with powerful IDE auto
-completion features during development of ULO applications.
-
-\subsubsection{Endpoints in \emph{ulo-storage}}
-
-We see that both SPARQL and RDF4J have unique advantages. While SPARQL
-is an official W3C standard and implemented by more database systems,
-RDF4J can be more convenient when dealing with JVM-based code bases.
-For \emph{ulo-storage}, we played around with both interfaces and
-chose whatever seemed more convenient at the moment. We recommend any
-implementors to do the same.
+with any value, that is it is a query variable to be filled by the
+call to \texttt{getStatements}.
+
+Using RDF4J does introduce a dependency on the JVM and its
+languages. But in practice, we found RDF4J to be quite convenient,
+especially for simple queries, as it allows us to formulate everything
+in a single programming language rather than mixing programming
+language with awkward query strings. We also found it quite helpful to
+generate Java classes from OWL~ontologies that contain all definitions
+of the ontology as easily accessible constants~\cite{rdf4jgen}. This
+provides us with powerful IDE auto completion features during
+development of ULO applications.
+
+Summarizing the last two sections, we see that both SPARQL and RDF4J
+have unique advantages. While SPARQL is an official W3C standard and
+implemented by more database systems, RDF4J can be more convenient
+when dealing with JVM-based projects. For \emph{ulo-storage}, we
+played around with both interfaces and chose whatever seemed more
+convenient at the moment. We recommend any implementors to do the
+same.
\subsection{Deployment and Availability}
@@ -291,17 +301,16 @@ environment for running a given application~\cite[pp. 22]{dockerbook}.
Docker Compose then is a way of combining individual Docker containers
to run a full tech stack of application, database server and so
on~\cite[pp. 42]{dockerbook}. All configuration of such a setup is
-stored in a Docker Compose file that describes the tech stack.
+stored in a Docker Compose file that describes the software stack.
For \emph{ulo-storage}, we provide a single Docker Compose file which
starts three containers, namely (1)~the Collector/Importer web
-interface, (2)~a database server for that web interface such that it
-can persist import jobs and finally (3)~a GraphDB instance which
-provides us with the required Endpoint. All code for Collector and
-Importer is available in the \texttt{ulo-storage-collect} Git
-repository~\cite{gorepo}. Additional deployment files, that is Docker
-Compose and additional Dockerfiles are stored in a separate
-repository~\cite{dockerfilerepo}.
+interface, (2)~a GraphDB instance which provides us with the required
+Endpoint and (3)~some test applications that use that Endpoint. All
+code for Collector and Importer is available in the
+\texttt{ulo-storage-collect} Git repository~\cite{gorepo}. Additional
+deployment files, that is Docker Compose and additional Dockerfiles
+are stored in a separate repository~\cite{dockerfilerepo}.
This concludes our discussion of the implementation developed for the
\emph{ulo-storage} project. We designed a system based around (1)~a
diff --git a/doc/report/introduction.tex b/doc/report/introduction.tex
index 3e95950bae4ff09bde056dd7a9a340a4c79ea270..d000ffbbc8a91b5b632045f96e4f7ea951876154 100644
--- a/doc/report/introduction.tex
+++ b/doc/report/introduction.tex
@@ -2,12 +2,12 @@
To tackle the vast array of mathematical publications, various ways of
\emph{computerizing} mathematical knowledge have been experimented
-with. As it is already difficult for human mathematicians to keep
-even a subset of all mathematical knowledge in their mind, a hope is
-that computerization will yield great improvement to formal research
-by making the results of all collected publications readily available
-and easy to search. In literature, this problem is referred to as the
-``one brain barrier''~\cite{onebrain}.
+with. Already it is difficult for human mathematicians to keep even a
+subset of all mathematical knowledge in their mind, a problem referred
+to as the ``one brain barrier'' in literature~\cite{onebrain}. A hope
+is that computerization will yield great improvement to formal
+research by making the results of all collected publications readily
+available and easy to search.
One research topic in this field is the idea of a \emph{tetrapodal
search} that combines four distinct areas of mathematical knowledge.
@@ -24,30 +24,32 @@ structure, tetrapodal search proposes that each kind of mathematical
knowledge should be made available in a storage backend that fits the
kind of data it is providing. With all four areas available for
querying, tetrapodal search intends to then combine the four indexes
-into a single query interface. Currently, research is focused on
-providing schemas, storage backends and indexes for the four different
-kinds of mathematical knowledge. The focus of \emph{ulo-storage} is
-the area of organizational knowledge.
+into a single query interface. Currently, research aims at providing
+schemas, storage backends and indexes for the four different kinds of
+mathematical knowledge. In this context, the focus of
+\emph{ulo-storage} is the area of organizational knowledge.
-A previously proposed way to structure such organizational data is the
+A previously proposed way to structure organizational knowledge is the
\emph{upper level ontology} (ULO)~\cite{ulo}. ULO takes the form of an
OWL~ontology~\cite{uloonto} and as such all organization information
is stored as RDF~triplets with a unified schema of
ULO~predicates~\cite{owl}. Some effort has been made to export
-existing databases of formal mathematical knowledge to {ULO}. In
+existing collections of formal mathematical knowledge to {ULO}. In
particular, exports from Isabelle and Coq-based libraries are
-available~\cite{uloisabelle, ulocoq}. The resulting data set is already
-quite large, the Isabelle export alone containing more than
+available~\cite{uloisabelle, ulocoq}. The resulting data set is
+already quite large, the Isabelle export alone containing more than
200~million triplets.
Existing exports from Isabelle and Coq result in a set of XML~files
that contain RDF~triplets. This is a convenient format for exchange
-and easily versioned using Git. However, considering the vast number
-of triplets, it is impossible to query easily and efficiently in this
-state. This is what \emph{ulo-storage} is focused on: Making ULO data
-sets accessible for querying and analysis. We collected RDF files
-spread over different Git repositories, imported them into a database
-and then experimented with APIs for accessing that data set.
+and easily tracked using version control systems such as
+Git~\cite{gitpaper} as employed by MathHub~\cite{mh}. However,
+considering the vast number of triplets, it is impossible to query
+easily and efficiently in this state. This is what \emph{ulo-storage}
+is focused on: Making ULO data sets accessible for querying and
+analysis. We collected RDF files spread over different Git
+repositories, imported them into a database and then experimented with
+APIs for accessing that data set.
The main contribution of \emph{ulo-storage} is twofold. First, (1)~we
built up various infrastructure components for making organizational
diff --git a/doc/report/references.bib b/doc/report/references.bib
index 723f84b0022db67aa9d7de292d6e74b126a0c37e..4c054689e1b98ded9f0d77bfc4dd608ed7a1391d 100644
--- a/doc/report/references.bib
+++ b/doc/report/references.bib
@@ -400,4 +400,23 @@
year = {2009},
urldate = {2020-09-27},
url = {https://www.w3.org/2009/sparql/wiki/Feature:PropertyPaths},
-}
\ No newline at end of file
+}
+
+@article{gitpaper,
+ title={GIT--A stupid content tracker},
+ author={Hamano, Junio C},
+ journal={Proc. Ottawa Linux Sympo},
+ volume={1},
+ pages={385--394},
+ year={2006},
+ publisher={Citeseer}
+}
+
+@incollection{mh,
+ title={System description: MathHub. info},
+ author={Iancu, Mihnea and Jucovschi, Constantin and Kohlhase, Michael and Wiesing, Tom},
+ booktitle={Intelligent Computer Mathematics},
+ pages={431--434},
+ year={2014},
+ publisher={Springer}
+}
diff --git a/doc/report/report.tex b/doc/report/report.tex
index 92df47a84f69c2e36482626c5cbbbe6ac4346309..d968805e13168023dca23b47085e7202832c85be 100644
--- a/doc/report/report.tex
+++ b/doc/report/report.tex
@@ -3,6 +3,7 @@
\usepackage{amsmath}
\usepackage{booktabs}
\usepackage{caption}
+\usepackage{fancybox, graphicx}
\usepackage{float}
\usepackage{geometry}
\usepackage{graphicx}