Notes, summaries, assignments, exams, and problems for Computers

Transport Layer Responsibilities

Tracking Individual Conversations

At the transport layer, each set of data flowing between a source application and a destination application is known as a conversation (Figure 1). A host may have multiple applications that are communicating across the network simultaneously. Each of these applications communicates with one or more applications on one or more remote hosts. It is the responsibility of the transport layer to maintain and track these multiple conversations.

Segmenting Data and Reassembling Segments

Data must be prepared to be sent across the media in manageable pieces. Most networks have a limitation on the amount of data that can be included in a single packet. Transport layer protocols have services... Continue reading "Responsibilities of the Transport Layer" »

A

• ATTACHMENT: A file that is sent with an email.
• BANDWIDTH: A measurement of the amount of information that a computer network can send or receive. High bandwidth allows images and websites to load quickly on the Internet.
• BANNER: A rectangular graphic on a website that advertises a business.
• CASE: An enclosure that holds the computer's components.
• CODE: A set of words and symbols that give instructions to a computer.
• CONTENT: The material on a web page, including text and graphics.
• CROP: To cut off unwanted parts of an image.
• DATABASE: A large group of data organized in a computer system. It allows you to search and find information easily.
• DESKTOP: Everything that a user sees on a computer screen.
• DESKTOP COMPUTER: A computer that is small enough to

KDD-- CRISP-DM = business understanding, data understanding, data prep, modeling, evaluation, deployment-- KDD- selection, preprocessing, transformation, mining, interp/eval-- classification = most frequently used, machine learning (supervised), output is nominal or ordinal categorical in nature -- assessment methods = predictive accuracy, speed, robustnest, scalability, interpretability-- confusion matrix formulae = accuracy = (TP + TN)/(TP+TN+FP+FN); true positive rate = (TP)/(TP+FN); true negative = TN/(TN+FP); precision = (TP)/(TP+FP); recall = (TP)/(TP+FN) -- overfitting = excessively complex model, can give bad predictions, underfitting- too flexible, also gives bad predictions-- k-fold cross validation- split data into k mutually exclusive... Continue reading "Data Mining and Machine Learning Techniques: A Comprehensive Overview" »

Web Requests: GET vs. POST

GET: The request displays the password in the browser URL.

POST: Does not remain in history and does not display the password or on the web server log, not displayed in URL.

Controlling Access to Resources

Lock: Use the database.

• Implement file lock.

Optimistic Concurrency Control

When using locks, there is a possibility of deadlocks.

Solution:

Use timeout: When starting the processing of a request, set a maximum execution timeout. When the timeout expires, the system suspects that a possible problem (such as a deadlock) has occurred.

When the timeout expires, which request should be aborted?

We may end up canceling a request that is almost complete.

Deadlock Prevention

To prevent deadlock, the system can set all the locks the... Continue reading "Web Requests, Concurrency Control & Distributed Systems" »

Software Crisis:

Software Myths:Management Myths:

1. Information System Definition and Functions

An information system is an organized system for the collection, organization, storage, and communication of information. It is the study of networks that people and organizations use to collect, filter, process, create, and distribute data. Essentially, it's a group of components that interact to produce information.

Objectives:

• Efficient management of data and information
• Improvement of business processes
• Creation of value

The main functions are:

• Capturing internal and external data
• Data processing
• Distributing information to users

2. Centralized vs. Distributed Information Systems

Centralized Systems

In a centralized system, all calculations are done on one particular computer.

Distributed Systems

In a distributed... Continue reading "Understanding Information Systems and Network Topologies" »

Phishing:

Hackers attempt to impersonate genuine organisations to fool the user into providing sensitive personal data. Emails are very official-looking, and they usually contain a link to a website which is an exact copy of the organisation's actual site, but it is operated by the criminals. When the user logs in with their details, the data is sent to the criminal. 

Guarding against phishing:

No reputable organisation would request personal details in an email or unsolicited phone call, because it does not need your sensitive data to access your account information. Never follow links to a bank/organisation- manually type it.

Trojan Horses:

Malware program that comes in disguise. Rely on tricking the user into downloading and running them. Involves... Continue reading "Protecting Against Phishing, Trojan Horses, Worms, and Viruses" »

Understanding HashMaps in Python

Introduction

This document demonstrates a simple implementation of a HashMap in Python. A HashMap, also known as a hash table, is a data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash function is used to compute an index into an array of buckets or slots, from which the desired value can be found.

Code Implementation

The following code provides a basic HashMap class in Python:

Loops

• // Loop forward
• for i in 0..
• // do something
• }
• // Loop in reverse
• for index in stride(from: 5, through: 1, by: -1) {
• print(index) // 5,4,3,2,1
• }
• // OR
• for i in (0..<10).reversed() {
• print(i)
• }

Strings

• // Convert String to Array of Strings containing 1 Character
• var strArr = str.characters.map { String($0) }
• // Join Array of Strings into 1 String
• var str = strArr.joined(separator: "")
• // Split String into array
• import Foundation
• let fullNameArr = fullName.components(separatedBy: " ")
• // Split String into Characters
• let subsequences = str.characters.split(separator: " ") // Returns array of Subsequence, not array of strings
• String(subsequences[0]) // to use as string
• // Convert String to Array of Characters
• sChars = Array(string.characters)

String/Character to