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* Opgave 1
Dette er opgave 2.1 fra bogen, på side 86.
** Del opgave A
#+BEGIN_QUOTE
Perform a horizontal fragmentation of relation EMP with respect /{ p1, p2 }/.
#+END_QUOTE
Her er /p1/ og /p2/ forklaret i opgaven.
| ENO | ENAME | TITLE |
|-----+----------+-------------|
| E1 | J. Doe | Elect. Eng. |
| E3 | A. Lee | Mech. Eng. |
| E6 | L. Chu | Elect. Eng. |
| E7 | R. Davis | Mech. Eng. |
|-----+----------+-------------|
| E2 | M.Smith | Syst. Anal. |
| E5 | B. Casey | Syst. Anal. |
| E8 | J. Jones | Syst. Anal. |
Desuden, wow hvor er tabel toolet her godt.
** Del opgave B
#+BEGIN_QUOTE
Explain why the resulting fragmentation /(EMP1, EMP2)/ does not fullfill the correctness of fragmentation.
#+END_QUOTE
Well i guess thats because p1 and p2 did not include "Programmer",
so now if you join the partitions you wont get the full thing.
** Del opgave C
#+begin_quote
Modify the predicates p1 and p2 so that they partition EMP obeying the correctless rules of fragmentation.
To do this, modify the predicates, compose all minterm predicates and deduce the corresponding implications,
and then perform a horizontal fragmentation of EMP based on these minterm predicates.
Finally, show that the result has completeness, reconstruction, and disjointness properties
#+end_quote
Okay so the predicates become:
\begin{align*}
p_1 &= \mathtt{TITLE} \leq "Programmer" \\
p_2 &= \mathtt{TITLE} > "Programmer"
\end{align*}
| ENO | ENAME | TITLE |
|-----+-----------+-------------|
| E1 | J. Doe | Elect. Eng. |
| E3 | A. Lee | Mech. Eng. |
| E6 | L. Chu | Elect. Eng. |
| E7 | R. Davis | Mech. Eng. |
| E4 | J. Miller | Programmer |
|-----+-----------+-------------|
| E2 | M.Smith | Syst. Anal. |
| E5 | B. Casey | Syst. Anal. |
| E8 | J. Jones | Syst. Anal. |
Nu kan vi se at completeness er opfyldt, og at ved at join de to partition får den originale tabel.
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