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\title{CS 448 Spring 2024 Homework 1}
\author{Sean Rettig}

\begin{document}
\maketitle

\section*{Question 1. (0.50 pts)}
\begin{enumerate}[(a)]
    \item Discuss the main capabilities that should be provided by a DBMS
    \item Highlight the difference of using a database system with respect to the following approaches. Please, make sure to highlight the benefits offered by a DBMS.
        \begin{enumerate}[1.]
            \item Traditional file systems
            \item In-memory storage
        \end{enumerate}
\end{enumerate}

\hrule

\begin{enumerate}[(a)]
    \item One of the main capabilities that should be provided by a databse include a self describing nature. The database shouldn't
        just store it's own data, but it should also store a complete definition of the database structure and it's constraints.

        Another capability should be an insulation between programs and data, otherwise called program-data independence. 
        This allows changing data structures and storage organization without having to change the DBMS access programs.

        Thirdly, there is data abstraction. The DBMS should provide a conceptual representation of it's data, and should hide the actual physical implementation. 
        
        The database should also support multiple view of the data.
        The user should not be limited to the actual positioning of the data, and should be able to view it in multiple ways. 
        
        Finally, the database should facilitate sharing of data and multiuser transaction processing. Multiple users should be able to access the data at the same time.
    \item \begin{enumerate}[1.]
        \item The traditional filesystem does not include the main characteristics of a DBMS well. There is no self describing nature in a filesystem,
            The program or software needs to know where the information is stored to be able to access it. There is no conceptual representation of the data either.
            Additionally, there are not multiple views of the data. Finally, sharing information is very difficult because traditional filesystems are very user focused,
            so if someone has information stored in their own filesystem place, it is not readily accessible by anyone else.
        \item It is not explicitely designated how in-memory storage would be designed. However, if the application software is storing everything in-memory and in the program that is running,
            all it takes is for the program to stop or the computer to shut down and the data will be gone.
    \end{enumerate}
\end{enumerate}

\newpage
\section*{Question 2. (0.50 pts)}
Cite some examples of integrity constraints that you think can apply to the database shown in
Figure 1.2 in the textbook. Please, provide at least two examples for each type of the following
constraints: unique constraints and referential integrity constraints
\hrule
\vspace{.5cm}
\noindent
Unique: Lets say that each section must have a unique section\_identifier, and each student must have a unique student\_number.
\\\\
\noindent
Referential: Each student\_number in the grade report must refer to a student in STUDENT. Each section identifier in GRADE\_REPORT must
refer to a section\_identifier in SECTION


\section*{Question 3. (0.25 pts)}
What is the difference between a database schema and a database state? Please, use examples to
support your answer.
\hrule
\vspace{.5cm}
\noindent
The database schema is the description of the database and what information it holds, and how it all relates to each other.
The database state is the current data actually in the database.\\\\
For example, in Figure 1.2, the database schema for the STUDENT table says that it includes the students name, Student\_number, Class, and Major.
The database state includes actual student names, and the rest of the information like Name: Smith, Student\_number: 17, Class: 1, Major: CS and then other students as well.


\section*{Question 4. (0.50 pts)}
\begin{enumerate}[(a)]
    \item What is logical independence and physical independence? Please, use examples to
    support your answer.
    \item Which one is harder to achieve? Explain why.
\end{enumerate}
\hrule
\vspace{.5cm}
\noindent
\begin{enumerate}[(a)]
    \item Data independence refers to the capacity to change different levels in the three scheme architecture without affecting each other.
        Logical independence is the ability to change the conceptual schema, while physical independence refers to the ability to change the internal schema.
        \\\\
        If you had logical independence, you could add a row to GRADE\_REPORT in Figure 1.2 and all the external views that
        call for data that is in the other columns will not be affected at all.

        If you had physical independence, you could change the way that GRADE\_REPORT is actually stored in the
        DBMS by creating a better way of accessing the data. The conceptual schema wouldn't cahnge and neither would the external schema.
    \item Logical independence is harder to achieve. This is because it allows structural and constraint changes, but you cannot affect application programs.
\end{enumerate}


\section*{Question 5. (0.50 pts)}
What are the different components of a DBMS? Discuss the importance and need of each
component.
\hrule
\vspace{.5cm}
\noindent
\begin{itemize}
    \item \textbf{Interfaces for DBA staff, Casual Users, Application Programmers, and Parametric Users}: This is important because
        the data is needed to be accessed, but not everyone needs the same type of access. Some need more advanced while others need simpler access.
    \item \textbf{DDL Compiler}: This prcoesses schema definitions. This is important to create the catalog.
    \item \textbf{Query Optimizer}: This component takes queries and looks for ways to optimize them. Either by consulting the catalog or through other means.
        It is important because it improves performance.
    \item \textbf{Precompiler}: This extracts DML commands and sends them to the DML compiler for compilation into object code.
        This is important to be able to communicate to the database.
    \item \textbf{Runtime Database processor}: This executes the commands, query plans, and transactions. This is important in accessing the database.
    \item \textbf{Stored Data Manager}: This uses basic operating system services for carrying out low-level IO to disk and main memory. It's important
        because the low-level IO needs to reach the higher level calls.
    \item \textbf{Concurrency control and Backup and Recovery systems}: Handle concurrency access as well as backup and recovery of the database. These are important 
        to support the main capabilities of the database being concurrency access and then another important feature of backup.
\end{itemize}

\section*{Question 6. (0.50 pts)}
\begin{enumerate}[(a)]
    \item What is a user transaction?
    \item What properties must be maintained for a transaction by the database system? Please,
    discuss each property using an example to support your argument.
\end{enumerate}
\hrule
\vspace{.5cm}
\noindent
\begin{enumerate}[(a)]
    \item A transaction, as the textbook says, is an execuiting program or process. It can include one or more database accesses.
        It can read or update records as well.
    \item Properties that the DBMS have must include isolation as well as atomicity. 
    
        Isolation ensures that each transaction takes place without effecting other transactions. This means that if I had one transaction asking
        for all the students in one class, but in the middle of that transaction I update the students in the class, the first transaction will 
        have the same result as if I didn't do the second one.

        Atomicity ensures that either all the databse operations in a transaction are executed or none are. For example, 
        if, in my transaction, I calculated GPA of all students and added that to their records, but my second operation doesn't complete successfully, then the first part of
        of my transaction will not execute.
\end{enumerate}

\section*{Question 7. (0.25 pts)}
Why is accessing a disk block expensive? Discuss the time components involved in accessing a
disk block.
\vspace{.5cm}
\hrule
\vspace{.5cm}
\noindent
It is expensive for a couple of reasons. Given the address, the disk controller must physically position the read/write head on the
on the correct track. This is called seek time and can take anywhere from 5 to 10 msec.\\
After seek time there is also rotational delay. This is waiting for the beginning of the desired block to rotate into position under the read/write head. For a 15,000 rpm (pretty fast) disk, the average rotational
delay is 2 msec.\\
After that there is actually transferring the data. This is called the block transfer time, which can differ between disks and OSes, but is generally less than
the seek time and rotational delay.\\
Thus, disk access time = seek time + rotational delay + block transfer time.
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