abstract = "Scientific progress relies on models that allow us to
describe, understand, and predict the behaviour of
real-world phenomena. Mathematical equations form the
backbone of many scientific models, offering a formal
and compact representation of our knowledge.
Traditionally, such equations were proposed or derived
by human experts. Recently, however, machine learning
(ML) methods have been used to discover equations
directly from data. A prominent example is symbolic
regression (SR), which searches for predictive models
in the form of mathematical expressions. Although SR
has been successful in uncovering many well-known
equations from physics, chemistry, and biology, its
performance becomes less certain when applied to
complex real-world datasets that do not lend themselves
to concise analytical descriptions. Yet for many such
datasets (e.g., in medicine), fully transparent models
are particularly valuable and often necessary. In this
thesis, I propose new classes of ML models that retain
key advantages of mathematical equations while not
being constrained to compact purely symbolic
expressions. As a result, they may be more flexible and
applicable to real-world settings. First, I introduce a
mathematical framework to characterise what makes some
equations easy to analyse. Then I build on these
insights to propose a new model class that extends SR
by univariate shape functions from generalised additive
models, thereby unifying the two approaches. The second
half of this work focuses on dynamic settings
(traditionally addressed by ordinary differential
equations). First, I investigate what it means for a
time series forecasting method to be fully transparent.
The next chapter leverages those insights to propose a
new approach to modeling dynamical systems called
direct semantic modelling. In contrast to the
traditional two-step modelling approach, where an
ordinary differential equation is first found and then
analysed, this framework directly outputs the
description of the system behaviour, making it easier
to understand, verify and edit. I introduce Semantic
ODE, an instantiation of the framework for
one-dimensional systems. Finally, I extend it to
multidimensional dynamical systems that may depend on
auxiliary static features.",