Notes, abstracts, papers, exams and problems of Computers

infile.Read(1)
'T'
>>>
infile.Read(5)
'he 3 '
>>>
infile.Readline()
'lines in this file end with the new line
character.\n'
>>>
infile.Read()
'\nThere is a blank line above this line.\n'
>>>
infile.Close()

outfile = open('test.Txt', 'w')
>>>
outfile.Write('T')
1
>>>
outfile.Write('his is the first line.')
22
>>>
outfile.Write(' Still the first line...\n')
25
>>>
outfile.Write('Now we are in the second line.\n')
31
>>>
outfile.Write('Non string value like '+str(5)+' must be converted first.\n')
49
>>>
outfile.Write('Non string value like {} must be converted first.\n'.Format(5))
49
>>> outfile.Close()

if temp > 86:
print('It is hot!')
print('Be sure to drink liquids.')
else:
print(... Continue reading "Which of the following statements is true?," »

Acid Rain: Concurrency-Related Attacks in Database-Backed Web Applications

Motivation:

• 12 popular self-hosted e-commerce applications (deployed over 2M websites, representing over 50% of all e-commerce websites)
• 22 critical ACIDRain attacks identified and verified
• Flexcoin -> Bankrupted

Problem Definition:

An application is vulnerable if:

• Anomalies Possible: Under concurrent API access, the application may exhibit behaviors (i.e., anomalies) that could not have arisen under serial execution.
• Sensitive Invariants: The anomalies arising from concurrent access lead to violations of application invariants.

Solution:

• Execute API calls against a live application and database to generate a (possibly sequential) trace of database activity.
• Analyze the trace

Understanding Computer Fundamentals

Output Devices

Plotter

A plotter is a specialized output device that generates images on paper, similar to a printer but with a distinct approach. Plotters excel at producing large-scale drawings or images, such as construction plans or blueprints. They can be connected to the same port typically used by a printer.

Tab Stops

Tab stops simplify document formatting. By default, they are set at 0.5-inch intervals from the left margin, allowing for easy creation of elements like tables of contents or indexes without manual adjustments.

Formatting and Data Visualization

Importance of Pie Charts

Pie charts effectively illustrate relative proportions or contributions to a whole using a single data series. Their effectiveness... Continue reading "Understanding Computer Fundamentals: Output Devices, Formatting, and Software Features" »

SkinnerDB: Regret-Bounded Query Evaluation via Reinforcement Learning

INTRODUCTION AND PROBLEM DEFINITION:

The work is on query optimization, more specifically: SkinnerDB focuses on finding the optimal Join Order. Because it has the most impact in practice.

SkinnerDB aims to get expected near optimal results without needing any a-priori information. It does not make strong assumptions either.

CONTRIBUTIONS:

• Introduced a new quality criterion for query evaluation strategies that compares expected and optimal execution cost.
• Proposed several adaptive execution strategies based on reinforcement learning.
• Formally proved correctness and regret bounds for those execution strategies.
• Experimental comparisations of those strategies, implemented in SkinnerDB,

The ER model defines the conceptual view of a database. It works around real-world entities and the associations among them. At view level, the ER model is considered a good option for designing databases.

Entity

An entity can be a real-world object, either animate or inanimate, that can be easily identifiable. For example, in a school database, students, teachers, classes, and courses offered can be considered as entities. All these entities have some attributes or properties that give them their identity.

An entity set is a collection of similar types of entities. An entity set may contain entities with attribute sharing similar values. For example, a Students set may contain all the students of a school; likewise a Teachers set may contain... Continue reading "Understanding the Entity-Relationship Model for Database Design" »

C Programming Basics

Printing a Message

Variables and Mathematical Calculations

Floating-Point Math

Arrays

List and Briefly Define the Four Main Elements of a Computer

A computer is composed of four fundamental elements:

• Main memory: Stores both data and instructions.
• Arithmetic and Logic Unit (ALU): Capable of operating on binary data.
• Control Unit: Interprets the instructions in memory and ensures their execution.
• Input and Output (I/O) Equipment: Operated by the control unit to facilitate interaction with the external world.

Define the Two Main Categories of Processor Registers

Processor registers can be broadly classified into two categories:

• User-Visible Registers: These registers are accessible to programmers using machine or assembly language. They help minimize references to main memory by optimizing register usage. High-level language compilers

• A class is a template used to create objects and declare data types and methods in a program.
• Public - Modifier used to declare classes and interfaces. Void - Method that returns no value. Main - Marks the start and end of program execution.
• Scanner class - Used to get user input for types like String and Int.
• Exceptions: Try-catch block, throw statement.
• Inheritance provides a powerful and natural mechanism for organizing and structuring software programs. It improves clarity in the design of classes.
• A subclass provides specialized behavior based on elements provided by the superclass. Using inheritance, programmers can reuse the code in the superclass many times.
• Reading and Writing to Files:
  1. Import java.io file.
  2. File inputFile = new File("input.