UV Distributed Information Management
Summer semester 2023
Questionnaire Assignment 1
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The purpose of this questionnaire is to deepen the student's understanding of
assignment 1 and the topics covered in the lecture. The main focus will be the
*correctness* and the *quality* of an answer, not its length. For some
questions, we will provide rough hints to give you a head start.

You are free to answer the questions directly in this textfile or use another
editor/word processor. The following file formats will be accepted for the
submission: .txt, .pdf, .odt, .doc, .docx. Please note that other file formats
will result in 0 points (for this questionnaire). The preferred file formats are
.txt and .pdf (most word processors support an export as PDF file). In any case,
please make sure that the questions/answers are named/numbered properly!

This questionnaire will be discussed during the after-assignment meeting. Before
the meeting starts, the group will be informed about the preliminary points by
the instructor (either at the beginning of the meeting or via Blackboard). The
final points will be set after the meeting. This questionnaire contributes a
maximum of 8 points to the overall points of assignment 1.

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Question F1:
Change query Q2 such that it only reports movies named 'The Avengers' that
started after 1990 (startYear). Please formulate the SQL query in the answer.
For query Q2, we refer to the assignment description. 

Answers A1:
<Your answer can go here>

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Question F2:
In the lecture, we discussed consistency constraints. Name and describe at least
two different consistency constraint of table 'names'. Is this a constraint on
a column or on the entire table?

Hints:
You can either look at the 'CREATE TABLE' statement in the file create_db.sql or
you can use the command '\d names;' to get some information about the table
(including the consistency constraints).

Answers A2:
<Your answer can go here>

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Question F3:
Consider the query plan of query Q4. Try to understand and (informally) describe
what information is provided by your query plan. Most importantly, what is the
link between the query and the query plan. Is the query plan declarative or
imperative? For reference, please also include the query plan that is reported
by your system.

Hints:
Your answer should be on an intuitive level, there is no need to understand all
the details (i.e., numbers) that are shown in the query plan. To understand the
terminology, we recommend to read the PostgreSQL documentation of the 'EXPLAIN'
statement (in particular, the first 3 explanations in the Basics section):
https://www.postgresql.org/docs/current/using-explain.html.
'Seq Scan' refers to a so-called sequential scan, that is, the database system
will simply read all the data of the respective table (from start to end).

Answers A3:
<Your answer can go here>

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Question F4:
You had two options to modify query Q3 (the COUNT aggregation in SQL and
Python3's len() function). Please briefly discuss the implications (pros and
cons) of the two options and justify your choice.

Hints:
Consider the efficiency aspect and try to think about "where" (or "by whom") the
actual work (counting the number of tuples) is performed.

Answers A4:
<Your answer can go here>