Notes, summaries, assignments, exams, and exercises for Computer science for University

JavaScript Regular Expressions: An Introduction

This concise and clear introduction to Regular Expressions (RegExp) in JavaScript covers their usage, modifiers, patterns, methods, and string integration.

Regular Expressions are powerful patterns used to match, search, and manipulate strings. In JavaScript, regular expressions are objects used with string methods to perform pattern matching.

RegExp Syntax Fundamentals

You can define a regular expression using literal notation:

const pattern = /expression/modifiers;

Or by using the RegExp constructor:

const pattern = new RegExp("expression", "modifiers");

RegExp Modifiers (Flags) Explained

Modifiers change how a Regular Expression behaves:

Python Coding Style: PEP 8

PEP 8: Indentation: Use 4 spaces. Line Length: Limit to 79 characters. Imports: Import on separate lines. Naming: Follow naming conventions. Comments: Explain non-obvious code. Whitespace: Use blank lines judiciously. Function Arguments: Use spaces after commas. Annotations: Follow type annotation guidelines.

Documentation: Use docstrings. Vertical Whitespace: Separate code logically. Imports Formatting: Organize import statements. Avoid Wildcard Imports: Be explicit. Consistency: Maintain consistency in style.

Four Core Programming Concepts

Four Big Programming Concepts: Abstraction and encapsulation, Parameterization, Iteration (loops), Expressions (calculations).

Understanding NamedTuple

NamedTuple: Named Fields: namedtuple...

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

Relational Keys

a) Advantage of Interrupts for Peripheral Devices

Explain the advantage of using interrupts as a technique for handling peripheral devices and relate it to computer performance. (10)

Answer

Interrupts offer a significant advantage because the processor doesn't need to constantly poll peripherals to check for data readiness. Instead, the peripheral alerts the processor when it's ready. This allows the processor to focus on other tasks while waiting for the peripheral, thus increasing overall computer performance.

b) Multiple Choice Questions on Interrupts

With regard to interrupts, check only what is correct in the following statements. (8) Explain why the last statement has been marked as correct. (7) Total 15 points

1.

To be considered an interrupt,...

Linux File System Structure: An archive of Linux is associated with 3 parts: superblock, inode table, and data blocks.

Network Ports: To see the ports assigned to services.

Display Active TCP/IP Connections: netstat -a

User Management:

• Create password: passwd (user)
• Add user to group: usermod -g group_name
• Disable: 60001
• Enable: 60002

Practical Commands:

Add User: adduser

1. Change folder privileges: chmod
2. Check privileges: ls -de (see if you changed privileges)

1. Create a user: useradd newuser
passwd newuser
2. Create a directory: The command mkdir is used to create directories:
   mkdir mydirectory
3. Create a report: ps -aux >> reporte.txt
4. Directories associated with the user: -d dirname
5. Changing permission: chmod 744 file.txt /file.txt
6. Change owner: chown
   Entering

Data Link Protocols

LAPB, LAPF, and LAPD

These are Data Link protocols:

• LAPB (Link Access Procedure, Balanced): A subset of HDLC, providing asynchronous balanced mode (ABM) for point-to-point links between user systems and packet-switching network nodes.
• LAPF (Link Access Procedure for Frame-Mode Bearer Services): Includes a control protocol (similar to HDLC) and a core protocol (subset of the control protocol). LAPF control uses ABM and 7-bit sequence numbers. LAPF core has flag, address, information, and FCS fields, but no control field.
• LAPD (Link Access Procedure, D-Channel): Provides data link control over the ISDN D channel. Uses ABM, 7-bit sequence numbers, a 16-bit CRC FCS, and a two-part address field for device and logical user identification.

Operating Systems

What are operating systems? This question can be answered at several levels.

Firstly, an operating system is a program, or a set of programs. Operating systems vary in size from very small to very large, but all are pieces of software. In the past, almost all operating systems were written in a low-level language. Currently, many operating systems are partly or completely written in a high-level language.

Secondly, an operating system is, by virtue of its name, a system. It is a collection of parts working together towards some common goals. The goals or objectives of an operating system may be regarded as the manager of these resources.

Thirdly, a computer may be regarded as a set of devices, or resources, which provide a number...