[DMDB] Completed normal forms, start query optimization

semester4/dmdb/parts/03_systems/00_query-optimization/00_intro.tex

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+A lot of performance can be gained in a database system by executing the query in the correct order.
+For that, a query optimizer exists, which uses a quite large amount of metadata to speed up query execution.
+
+A query optimizer very broadly works as follows:
+\begin{enumerate}
+    \item It searches the space of equivalent execution plans. This space tends to be huge, so efficient exploration is needed.
+    \item Of all the discovered plans, the best is chosen using a cost model, which describes the most efficient plan
+\end{enumerate}