GIT 215 Zybooks M1

IoT devices display one or more of the following characteristics:

- Gather information about the physical world using sensors. Ex: temperature, voltage, images. - Share the sensor data with control systems. Ex: A sensor may report a room's temperature to building control system, or air ozone and water pollution sensors reporting air quality data to urban environment monitoring systems. - Interact with hardware to execute commands sent by control systems. Ex: Speed up fan moving hot air to part of a building where the sensed temperature is below the target temperature.

Developers of mobile-friendly webpages need to consider the following:

- Screen size: Screen size is much smaller than desktops. - Load speed: Mobile devices may have limited or slower internet connectivity. - Device speed: Limited memory and CPU speed of mobile devices means mobile browsers are not as powerful as desktop browsers. - Data cost: Many users have data plans that limit how much content can be downloaded. Large webpages and webpages that keep requesting more data reach a mobile data plan's limit faster. - Battery life: A webpage that constantly runs JavaScript and frequently loads data will drain the battery faster. - Interface: User interaction is with touch, not a mouse.

Steps in an HTTPS transaction.

1. Browser requests an HTTPS connection to a webpage (The URL must begin with "https://".) 2. Web server sends digital certification to browser (The browser warns the user if the digital certificate is not from a trusted certificate authority.) 3. The browser and web server initiate "TLS handshake" (The browser and web server use the TLS handshake to generate session keys used to encrypt and decrypt information. A "handshake" is a networking term that means two participants communicate back and forth in order to negotiate a solution.) 4. The browser and web server transmit encrypted information (The encrypted information can only be decrypted by the browser and web server.)

An HTTP request and an HTTP response are both composed of four parts:

1. Start line - The start line specifies the HTTP version being used. A request's start line includes a request type and path; a response's start line includes a status code and phrase. 2. Zero or more header fields - A header field is a keyword followed by a colon and a value. Header fields supply additional information about the request or response. 3. Empty line 4. Optional message body - A message body contains data being transferred between a web browser and web server. In a request, the message body may be empty or contain submitted form data. In a response, the message body may contain the requested resource.

The IDEA of hypertext was founded in _____

1945

The TERM hypertext was coined in ______

1965

When was the first website published?

1991

If a web browser sends 20 HTTP requests to a web server, how many HTTP responses will the web server likely send to the web browser?

20 Every HTTP request usually results in a single HTTP response. However, a web server can ignore a request and fail to send a response.

In what year did the number of internet users surpass 3 billion?

2015

In what year did web browsing first become more likely on mobile rather than desktop?

2016

A browser redirect is when the web server returns a _________

301 or 302 status code with a Location header indicating the URL the browser should load next.

How many total HTTP requests does a browser send for a webpage that contains four web resources: an image, a video, a CSS stylesheet, and a JavaScript file?

5 One HTTP request is made for the HTML file, and one request is made for each resource. The browser may send multiple requests in parallel to speed-up the transfer of resources.

"The website is not responding" or "Could not reach the website". means:

A domain name may be found (so a valid IP address exists for that name) but the web server may not respond, non-response could be due to the web server being turned off or undergoing maintenance, or due to an essential router malfunctioning, for example.

IPv6

A newer 128 bit IP address which allows for many more devices to be addressed; coexists with IPv4

Responsive web design

A web design approach that creates webpages that automatically move and resize parts depending on the display size and orientation.

Mobile first web design

A web development approach that advocates first creating a reduced-feature version of a website for mobile users. Then, the developer creates a full-featured website for visitors using desktop computers.

_______ specifies the layout and visible appearance.

CSS

URL Scheme

Characters at the beginning of a URL followed by a colon ":" or a colon and double slashes "://". Common URL schemes include http, https, mailto, and file. Ex: In https://www.cdc.gov/alcohol, the scheme is "https".

HTTP/3,

Currently in development, improves the speed of HTTP/2 by using UDP to transport data packets instead of TCP.

Before a TCP connection is created, the web browser performs a/an

DNS lookup

Root Servers

DNS servers that keep a database of addresses of other DNS servers managing top-level domain names. and a computer's operating system or an ISP keeps a reference to the root servers' IP addresses. Ex: 198.41.0.4 (run by Verisign), 192.228.79.201 (run by USC), 199.7.91.13 (run by Univ. of Maryland), and 192.203.230.10 (run by NASA). The first step of sending an internet packet to a domain name is thus to lookup the IP address via a DNS server.

Last-Modified Header

Datetime the requested resource was last modified on the web server. The last modified datetime is usually available for static files on the web server. For resources that are dynamically created by the web server, the last modified datetime is often not provided.

Date Header

Datetime the response was generated by the web server. Datetime values in HTTP headers are represented in Greenwich Mean Time (GMT), which is equal to Coordinated Universal Time (UTC).

Common HTTP response status codes

EX: Code, Status phrase, Meaning 200, OK, Standard response for a successful request. 301, Moved Permanently, The resource should always be requested at a different URL. 302, FoundThe resource, should temporarily be requested at a different URL. 304, Not Modified, The resource has not been modified since the last time the resource was requested. 403, Forbidden, The web browser does not have permission to access the resource. 404, Not Found, The resource could not be located. 500, Internal Server Error, Something unexpected happened on the web server.

True OR False If a web server is down (such as powered off), the server may return a page saying to please try again later.

False If a server is down, the server cannot return a page. Instead, a message may be displayed saying "Cannot reach the website" or similar.

True OR False: Websites have either an IP address or a domain name, but not both.

False: All websites have an IP address. A domain name provides an easy-to-remember name for an IP address.

The Internet began as __________

Four networked computers in 1969. Today, the internet is the largest and most popular computer network, spanning the entire globe.

Common HTTP request methods.

GET: Request a representation of the specified resource. HEAD: Request a response identical to GET but without the response body. POST: Create a new resource with the contents of the message body. PATCH: Modify an existing resource with the contents of the message body. PUT: Replace an existing resource with the contents of the message body. DELETE: Delete an existing resource.

_______ defines the structure and content of a webpage.

HTML

WHATWG produces the _____ which is a _____

HTML Living Standard, a continually evolving standard without version numbers that replaces HTML5.

Text files, known as _______ , containing links to other text files.

HTML files

Where can the HTTP header field If-None-Match be found?

HTTP Request

The rules made for for transferring HTML files among computers

HTTP protocol

________ is the standard markup language for web documents.

HyperText markup language (HTML)

Are human doctors or IBM's Watson more likely to keep up with new medical information in the future?

IBM's Watson

User-Agent Header

Identifies the browser making the request. Browsers often identify themselves using a unique string of characters. The User-Agent field may be used by a web server to respond back with different resources depending on which browser made the request. Ex: A desktop page may be sent back to a desktop Chrome browser, but a mobile webpage may be sent back to an iPhone browser.

Server Header

Identifies the web server software that generated the response. Popular values for Server include Apache, Microsoft-IIS, and nginx.

Which browser lost the most market share between 2010 and 2019?

Internet Explorer (IE)

_______ describes the dynamic behaviors and actions of a webpage.

JavaScript

Is www.nasa.gov a valid URL?

No The protocol identifier https:// is missing. A web browser will assume the user meant https://www.nasa.gov and go to NASA's web page.

Do web servers always generate ETags for all web resources?

No, ETags are not often produced for dynamic web content.

Content-Length Header

Number of bytes in the response's message body. The web browser uses the content length to determine how much data to expect from the web server.

Content-Type Header

Number of bytes in the response's message body. The web browser uses the content length to determine how much data to expect from the web server.

How many total HTTP requests does a browser send for a webpage that does not use any other web resources?

Only one HTTP request is made for the HTML file.

URL Fragment

Optional characters at the end of a URL that start with a hash character (#) and refer to a certain location within a webpage. In https://en.wikipedia.org/wiki/URL#History, the fragment "#History" refers to the webpage's History section.

URL Query String

Optional characters to the right of the question mark (?) in a URL that provide data for the web server. In https://www.youtube.com/watch?v=uu7XCEMdSHg, the characters after the ? tells YouTube's server to play a video having code uu7XCEMdSHg.

Which request method is used by the browser to submit web form data to the web server?

POST

Screen Size is ____

Physical dimension in pixels of a device's screen. Mobile device screens are much smaller than desktops. Good design requires significant effort to make websites that work well for different screen sizes.

5 parts of a URL

Scheme, Hostname, PAth, Query string, Fragment

Given the following URL: http://www.gardens.com/flowers/iris.zip, what is the URL's scheme, hostname, and path?

Scheme: http Hostname: www.gardens.com Path: /flowers/iris.zip

Headers found in responses

Server, Last-Modified, Location, Expires, Content-Type,

URL Path

The characters to the right of the hostname in a URL. Ex: In https://www.cdc.gov/alcohol, the path is "/alcohol".

URL Hostname

The complete domain name following the scheme in a URL. Ex: In https://www.cdc.gov/alcohol, the hostname is "www.cdc.gov".

Separation of concerns is ___________

The design principles of breaking up web content using distinct languages and documents that overlap as little as possible. In modern web design, document structure and text, visual layout, and page interaction are separately specified using three key languages. 1. HTML is the language that describes the page content. 2. CSS is the language that describes page layout. 3. JavaScript is the language that provides interactive functionality. When webpages are built so as to cleanly separate document structure, visual layout, and interaction, the following results are obtained: - Webpages are more likely to work as intended across a wide range of browsers. - Webpages work better on smartphones and other mobile devices. - Internet of Things systems are easier to build because relevant data is easier to identify. - Web accessibility is improved. - Intelligent systems can extract more meaning from the content of webpages.

Host Header

The domain name for the requested path. Some websites are hosted at the same IP address, so the Host field helps the web server determine which website's resource is being requested.

IPv4

The original Internet Protocol, has 32-bit addresses

Which file does the following URL access?http://www.weather.com/summer/temperatures.html

The subfolder is summer, and the file is temperatures.html.

An internet packet contains ______

To and From IP addresses, the information to communicate, and other configuration information.

True OR False: Web developers can sometimes ignore really old web browsers.

True, Every browser eventually reaches obsolescence and can be ignored when developing typical sites.

Headers found in requests

User-Agent, If-None-Match, Host,

Affordances are _____

Visual clues that guide the user in figuring out how to use an app. Affordances, a term invented by usability expert Donald Norman, are harder to implement for mobile devices. For instance, few mobile devices support a touch screen equivalent of hovering with a mouse. So, hovering-based interfaces like tooltips are unavailable on touch based devices.

In 2019, the W3C relinquished HTML standards publishing to the ______ which is an ________

Web Hypertext Application Technology Working Group (WHATWG) organization that develops a variety of web standards

"Sorry, the website www.xyz.blahblahblah cannot be found." means:

a domain name is not found by a DNS server (usually because the domain name is not registered)

Domain Name System (DNS)

a name for an IP address, such as the name wikipedia.org for the IP address 198.35.26.96; the name is easier to remember and type. Capitalization doesn't matter: Wikipedia.org, wikipedia.org, and WIKIPEDIA.ORG are treated the same.

A Web browser is a ______

a program that downloads an HTML document from a web server, displays the document to the user with the appropriate formatting, and allows the user to interact with the document, such as clicking hyperlinks to access other documents. A web browser uses HTML to understand the structure and semantics, or meaning, of the document.

Transmission Control Protocol/Internet Protocol (TCP/IP) is _____

a protocol suite that governs how data packets are transferred over the internet from one machine to another. Understanding the details of TCP/IP is not usually required of web developers, but a thorough understanding of HTTP is necessary to create effective web applications.

HTTP/2

a relatively new HTTP standard that speeds-up the transfer of information between web browsers and web servers. HTTP/2 maintains most of HTTP/1.1's semantics

404 Status Code

a web server is reached but the specific requested page isn't found

What does a computer network do?

allows computers to communicate information with each other

FTP (File Transfer Protocol) was _________

an early way for transferring files over the internet. Users used FTP programs to connect to servers, look at listings of available documents, and download documents of interest

A Web Resource is ___

any retrievable item, like an HTML file, image, video, CSS stylesheet, etc.

A browser cache is an

area on the computer's file system where web content can be stored by the web browser for quick retrieval later. By caching web content, browsers can reduce the amount of network traffic required to display previously visited webpages. Ex: If a webpage is accessed now and again ten minutes from now, the browser can display the cached webpage instead of re-downloading the webpage. If the webpage has changed in the 10 minute span, the browser should download the updated page.

HTTPS uses a protocol called Transport Layer Security (TLS), which uses ________

asymmetric public keys to encrypt data between the browser and web server. A website wanting to use HTTPS must acquire a digital certificate, issued by a trusted certificate authority, that contains a public key used by TLS to encrypt data.

A program, known as a _______ , was created for viewing HTML files.

browser

second-level domain

commonly an organization's name as in Stanford.edu, or indicates the purpose of a website as in DoPython.org the wikepedia in wikepedia.com

An IP address (short for Internet Protocol address) is a

computer's unique address on the internet (like a house's unique address in the world), usually represented numerically like 198.51.100.7. A typical IP address is 32 bits, divided into four 8-bit groups, each group often written as a decimal number.

When a computer sends a packet using a domain name over the internet, the first step is to

contact a DNS server to convert the domain name to an IP address

Expires Header

contains a date/time indicating when the requested resource is considered "stale". Ex: "Expires: Wed, 01 Sep 2019 13:24:52 GMT" tells the web browser to show the cached resource until Sep 1, 2019 at 13:24:52 GMT.

each country is assigned a unique two-letter ____

country code top-level domain (ccTLD) like .uk (United Kingdom), .ru (Russia), and .de (Germany

________ markup is special markings in the document that provide additional information about links, formatting, and images

document

The period when the web was first developed.

early 1900's

Which scheme should a URL use to provide a secured HTTP connection to a web server?

https The https scheme encrypts web traffic, allowing users to safely submit sensitive information like credit card numbers to a website.

____ is text that has links to other text (and today to images, videos, and more)

hypertext

An entity tag (ETag) is an

identifier for a specific version of a web resource. Ex: 34905a3e285dd11. When the resource changes, so should the ETag associated with the resource. When a web browser requests a cached web resource, the browser sends the ETag in the request with an If-None-Match header. The web server will reply with a 304 Not Modified response status if the resource has not changed or a 200 OK with the changed resource and a new ETag.

The World Wide Web Consortium (W3C) is the ______

international standards organization that traditionally has controlled a number of web standards, including HTML. HTML5 was the latest HTML standard released by the W3C in 2014.

The Internet Assigned Numbers Authority (IANA)

is a standards organization that manages various internet numbers and symbols, like global IP address allocation, root zone management in DNS, and media types. IANA maintains a list of HTTP headers that are currently active, obsolete, or experimental.

Cache-Control Header

is used to specify a number of caching directives. Ex: "Cache-Control: no-store" tells the web browser to never cache the requested resource, and "Cache-Control: max-age=180" tells the browser to cache the resource for 180 seconds.

If-Modified-Since HEADER

is used with the Last-Modified date/time to request the web server only send the requested resource if the resource has changed since the specified date/time. Ex: "If-Modified-Since: Wed, 01 Sep 2019 13:24:52 GMT" asks the web server to send the resource if the resource was modified after Sep 1, 2019 at 13:24:52 GMT.

top-level domain

last portion of a web name; includes examples such as ".com", ".org" or ".net"

An HTTP request is a

message sent from the web browser to the web server. Often the request asks the web server to send back a web resource like an HTML file, image, CSS stylesheet, JavaScript file, or video.

An HTTP response is a

message sent from the web server back to the web browser in response to an HTTP request. Often the response contains the requested web resource.

Web developers can view 304 Not Modified responses in Chrome's DevTools by ________

opening the Network tab and ensuring the checkbox labeled "Disable cache" is not checked. If "Disable cache" is checked then nothing will be cached, and If-None-Match and If-Modified-Since headers will not be sent.

The most common HTTP request-response scenario is when the web browser issues a request with the GET request method, and the web server _______

returns the requested resource with a 200 status code

A computer communicates with another computer on the internet by ______

sending packets back and forth

The web browser performs a DNS lookup by ___

sending the domain name to the local DNS and getting back the IP address of the web server hosting the domain name. Ex: https://www.w3c.org/ has a domain name of w3c.org, and DNS translates w3c.org to the IP address 193.51.208.66. The web browser uses the IP address to establish a TCP connection with the web server and begins communicating with HTTP.

A Network Sniffer is ________

software that monitors network traffic and allows users to inspect HTTP requests and responses. HTTPS encrypts HTTP traffic between a browser and web server so a network sniffer cannot intercept sensitive information in the HTTP traffic like passwords, credit card numbers, financial transactions, etc.

Third-level and further level domains refer to ______

sub-computer systems local to an organization, as in cs.stanford.edu where the cs is for Stanford's Computer Science department. A common third-or-deeper-level domain is www, short for World Wide Web, usually referring to an organization's web server. Many organizations use www optionally, so stanford.edu by default goes to www.stanford.edu.

top-level domains (TLD)

such as .com, .net, .org, .edu, and .gov.

HTTP/1.1

the HTTP standard used for most of the web's lifetime

Web accessibility is _____

the ability of users with disabilities to access and use a webpage with reasonable effort. Designing accessible webpages ensures equal access and opportunity for everyone. Developing accessible webpages requires knowledge of disabilities, assistive technologies and software used by users with disabilities, and following design practices to ensure content is compatible with those assistive tools. Some conditions affecting web accessibility include: - Visual problems like blindness, low vision, or color blindness - Hand control issues ranging from tremors to total inability to use hands - Seizures caused by flashing on the screen - Cognitive challenges like dyslexia and other difficulties in processing webpages

A DNS server's primary role is to convert _____.

the domain name to an IP address

Linkrot is ___

the general name for a once valid link that now returns a 404 status code.

The Internet of Things (abbreviated as IoT) is ________

the global collection of communicating devices that sense and control technology on behalf of humans. IoT devices range from a simple temperature sensor to a satellite-based laser scanner used to discover archaeological sites hidden by vegetation.

A URL (Uniform Resource Locator) is ____

the location of a web resource on the web, such as http://www.cdc.gov/alcohol/faqs.htm

ICANN

the organization that manages TLDs, now allows companies and organizations to create customized TLDs, like .church, .pizza, and .music

URL shortening

the translation of a long URL into an abbreviated alternative that redirects to the longer URL with a 301 status code

Cognitive computing is _____

the use of artificial intelligence techniques and access to vast amounts of data to simulate human problem solving in complex situations with ambiguity, changing data, and even conflicting information. When processing webpages, intelligent systems like Watson are aided by effective use of webpage HTML metadata and structure markup. Ex: Text containing digits is more useful when the digits are placed in an HTML table with a title like "Pacemaker failure rates".

An HTTP response status code is a

three digit number that indicates the status of the requested resource

a _______ is a program that serves webpages to web browsers.

web server

___________ is a document that is viewed in a web browser

webpage or web page

A collection of related webpages are organized into a ______

website

The World WIde Web (W3) is a ________

wide-area hypermedia information retrieval initiative aiming to give universal access to a large universe of documents

What is the hostname of the following URL?http://www.weather.com/summer/temperatures.html

www.weather.com

Is the following a valid URL? https://www.whitehouse.gov/

yes

Is the following a valid URL?https://www.nasa.gov/cubequest/details/#.VOaO_VPF9U9

yes