Commit 22318f9c authored by Ulrich's avatar Ulrich

reworked introduction

parent 0625eed9
......@@ -182,29 +182,115 @@ Erlangen, \today
%and therefore the requirement for barter trade.
it is thus not surprising that the first detected human measurements were done at least 30,000 years ago~\cite{haustein2001weltchronik}\ednote{Give a concrete example of such a measurement}.\ednote{describe the meaning of
measurement in this case}.
In former times, length, for instance, was measured in comparison to the human body, like in the case
In former times, length, for instance, was measured in comparison to parts of the human body, like in the case
of the units feet and cubit. Without a fixed value for these terms, we can regard the information that, for
instance, a house
has a height of 10 feet only as a loose estimate. The exact value depends on the length of the compared foot, which
is obviously impractical as a common system.
This problem can be solved by defining exact values for the terms.
Like this, we get fixed \textit{units} -- like the modern unit feet as a measure for length.
Now we can use \textit{quantity expressions}, say again 10 feet, to describe exact distances.
However different units with different values arose in different societies.
Today there are two predominant systems of measurement, the imperial system and the metric system.
Nowadays the latter is officially accepted in nearly all countries, but the former is still in use in many
countries of the former British Empire.
The latter is nowadays officially accepted in nearly all countries, but the former is still in use in many
countries that were part of the old British Empire.
The mixture of both systems already caused expensive errors like the crash of the
Mars Climate Orbiter~\cite{marsorbiter} in 1999. It happened because a part of the program calculated the impulse
Mars Climate Orbiter in 1999~\cite{marsorbiter}. It happened because a part of the program calculated the impulse
of the spacecraft in imperial units, namely in pound-seconds, while a different module expected the impulse
in Newton-seconds -- a metric unit -- as an input. The miscalculation lead to a wrong
position of the spacecraft that finally caused the crash.
in newton-seconds -- a metric unit -- as an input. The resulting miscalculation lead to a wrong
position of the spacecraft which finally caused the crash.
Efforts for a uniform system of measurement resulted in the International System of Units (abbreviated as SI) which
was resolved in 1960~\cite{ptbsi}. It is based on the seven basic units meter, kilogram, second, ampere,
kelvin, mol and candela. For convenience, the system also contains many units that can be derived from the
basic units. For instance Watt, a unit for power, is defined in terms of basic units as
Efforts for a uniform and modern system of measurement resulted in the International System of Units
(abbreviated as SI) which
was resolved in 1960~\cite{si2006}. It is based on the seven basic units meter, kilogram, second, ampere,
kelvin, mol and candela. Their value is derived mostly from natural constants. For instance, the second is defined as
``the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the
ground state of the caesium 133 atom.''~\cite[Page 113]{si2006} and the meter as
``the length of the path travelled by light in vacuum during a
time interval of 1/299 792 458 of a second.''~\cite[Page 112]{si2006}.
Table~\ref{tab:sibaseunits} shows the base units and their symbols together with the property they measure -- the physical dimension.
\begin{table}
\center
\begin{tabular}{|l|l|}
\hline
SI base unit & Physical Dimension \\
\hline
meter (m) & length \\
kilogram (kg) & mass \\
second (s) & time, duration \\
ampere (A) & electric current \\
kelvin (K) & temperature \\
mole (mol) & amount of substance \\
candela (cd) & luminous intensity \\
\hline
\end{tabular}
\caption{The SI base units, their symbols and their corresponding physical dimensions.
This table corresponds to Table 1 on Page 116 in~\cite{si2006}.}
\label{tab:sibaseunits}
\end{table}
For convenience, the system also contains many units that can be derived from the
basic units without any additional numerical factor.
For instance Watt, a unit for power, is defined in terms of basic units as
$1 \; \rm W = 1 \; \rm kg \cdot \rm m^2 \cdot \rm s^{-3}$ and Ohm, a unit for electrical resistance, is defined as
$1 \; \rm \Omega = 1 \; \rm W \cdot \rm A^{-2} = 1 \; \rm kg \cdot \rm m^2 \cdot \rm s^{-3} \cdot \rm A^{-2}$.
Table 2 to 4 in~\cite[Page 117ff]{si2006} list derived units and their definition in SI base units.
We omit a separate table here.
Decimal fractions and multiples of SI units can be formed with a fixed set of SI prefixes, which are shown in
Table~\ref{tab:siprefixes}. They range from $10^{-24}$ to $10^{24}$.
The kilogram already contains a prefix in its normal form, because its value is defined by the mass of the
international kilogram prototype.
\begin{table}
\center
\begin{tabular}{|c|c||c|c|}
\hline
Factor & Name (Symbol) & Factor & Name (Symbol) \\
\hline
$10^1$ & deca (da) & $10^{-1}$ & deci (d) \\
$10^2$ & hecto (h) & $10^{-2}$ & centi (c) \\
$10^3$ & kilo (k) & $10^{-3}$ & milli (m) \\
$10^6$ & mega (M) & $10^{-6}$ & mirco (\textmu) \\
$10^9$ & giga (G) & $10^{-9}$ & nano (n) \\
$10^{12}$ & tera (T) & $10^{-12}$ & pico (p) \\
$10^{15}$ & peta (P) & $10^{-15}$ & femto (f) \\
$10^{18}$ & exa (E) & $10^{-18}$ & atto (a) \\
$10^{21}$ & zetta (Z) & $10^{-21}$ & zepto (z) \\
$10^{24}$ & yotta (Y) & $10^{-24}$ & yocto (y) \\
\hline
\end{tabular}
\caption{SI prefixes -- compare Table 5 in~\cite[Page 121]{si2006}.}
\label{tab:siprefixes}
\end{table}
Nevertheless, not only imperial units -- like miles, square mile feet and Fahrenheit --
are still widely used, but also very specialized units in their certain fields
-- such as solar masses in astronomy,
atomic mass units in particle physics and electron volt in high energy physics.
For people who are not familiar with these units, their occurrence makes
the understanding of texts more complicated.
As an example a recipe in fluid ounces and quart requires some calculations to
translate it to, say, milliliters for a person who is used to metric units.
We have already seen that inaccuracies in such calculations not only cause unpleasant-tasting
dishes, but, in more complicated contexts, can cause dramatic errors like the crash of the Mars Orbiter.
Computer programs can help for this problem. Many simple unit conversion tools and web-services are
already available. However they require the user to leave his document in order to open the conversion service.
The automatic conversion of complete documents from one system of measurement to another, say from imperial to
metric, is a much more difficult task, which we will investigate in this thesis.
At first, this requires to detect quantity expressions in a given document. For that, we need to infer
the meaning of a sequence of characters and we thus refer to such challenges as \textit{meaning extraction}.
After that, we can offer \textit{semantic services} -- services which exploit the meaning of the document --, like
the automatic conversion of imperial units to metric ones.
Additionally, we also exploit the semantics of the detected quantity expressions in two other ways.
One is an improvement for MathWebSearch, a search engine for mathematical formulae \cite{kohlhase2006search},
by adding the meaning of the detected quantity expressions to the system. Like this, when we search for formulae
containing, say, 42 kilometers, our results can also include equivalent values in other units like 26 miles.
The last semantic service is an enhancement for screen reading programs for blind users, which allows them
to read the meaning of a quantity expression instead of or in addition to its presentation, say ``1500 Volt'' and
not only ``1500 V''.
% Subsequently there is an interest to standardize the value of units, which resulted in
......@@ -216,17 +302,14 @@ Erlangen, \today
%
% Imperial and metric units are well-known examples of different systems of measurement.
% Their mixture already caused expensive errors like the crash of the Mars Climate Orbiter, where one team
% worked with imperial units while another one used metric units~\cite{marsorbiter}.
It is based on the seven units
Nevertheless, many different and often specialized units are still used, like solar masses in astronomy and
electron volt in high energy physics.
Semantic services can simplify the work with quantity expressions and units and this thesis thus provides a framework
for the detection of quantity expressions in documents from the fields of science, technology, engineering and
mathematics (STEM). The findings are then exploited by three semantic services. The first one is an application for
the automatic conversion of units and the second one creates input suitable for MathWebSearch, a search engine for
mathematical formulae~\cite{kohlhase2006search}. The last service is an enhancement for screen readers with semantic
information.
%% worked with imperial units while another one used metric units~\cite{marsorbiter}.
% Semantic services can simplify the work with quantity expressions and units and this thesis thus provides a framework
% for the detection of quantity expressions in documents from the fields of science, technology, engineering and
% mathematics (STEM). The findings are then exploited by three semantic services. The first one is an application for
% the automatic conversion of units and the second one creates input suitable for MathWebSearch, a search engine for
% mathematical formulae~\cite{kohlhase2006search}. The last service is an enhancement for screen readers with semantic
% information.
%
\subsection{Related Work}
\label{ssec:relatedwork}
......
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