5.1 · The internet and the world wide web
5.1 · 互联网与万维网
The internet and the world wide web
互联网与万维网
What the internet actually is and how the web sits on top of it, the parts of a web address, the two transfer protocols, what a browser is for, the exact sequence from typing a URL to seeing the page, and what a cookie really is.
互联网到底是什么、万维网如何建立在它之上、一个网址由哪些部分组成、两种传输协议、浏览器是干什么的、从输入 URL 到看见网页的确切顺序,以及 Cookie 究竟是什么。
Explainer · 5.1.1
讲解 · 5.1.1
The internet is not the web
互联网不等于万维网
People say "the internet" and "a website" as if they mean the same thing. They do not. One is the wiring; the other is one of the things that travels along it.
人们说"互联网"和"网站"时,好像它们是一回事。其实不是。一个是"线路",另一个是在这条线路上传输的东西之一。
The internet is the infrastructure: the worldwide system of interconnected computer networks, and the hardware that joins them together, such as cables, routers and servers.
互联网是基础设施:全球范围内相互连接的计算机网络系统,以及把它们连在一起的硬件,例如电缆、路由器和服务器。
The world wide web (WWW) is the collection of websites and web pages that are accessed using the internet. The pages are written mostly in HTML, joined by hyperlinks, and viewed in a web browser.
万维网(WWW)是通过互联网访问的网站和网页的集合。这些网页主要用 HTML 编写,通过超链接相互连接,并在网页浏览器中查看。
Sending an email, making a video call and transferring a file all use the internet too, but they are not part of the web. The web is one service running on the internet, not the internet itself.
发送电子邮件、进行视频通话、传输文件,这些也都在使用互联网,但它们不属于万维网。万维网是运行在互联网上的一项服务,而不是互联网本身。
Keep the two definitions separate and precise: internet = the infrastructure (networks and hardware); web = the websites and web pages reached over that infrastructure.
把两个定义分开、说准确:互联网 = 基础设施(网络和硬件);万维网 = 通过这套基础设施访问到的网站和网页。
Explainer · 5.1.2
讲解 · 5.1.2
The URL: a web address in words
URL:用文字表示的网址
A URL (uniform resource locator) is the address of a web page written out as text. It can contain three parts:
URL(统一资源定位符)是一个网页的地址,以文字形式写出。它可以包含三个部分:
| Part | 部分 | Example | 示例 | What it says | 它表示什么 |
|---|---|---|---|---|---|
| Protocol | 协议 | https:// | https:// | the set of rules used to transfer the page | 用来传输该网页的规则集合 |
| Domain name | 域名 | www.examedge.app | www.examedge.app | names the web server that holds the site | 指明保存该网站的网页服务器 |
| Web page / file name | 网页 / 文件名 | /learn/notes.html | /learn/notes.html | which page or file on that server is wanted | 要访问该服务器上的哪个网页或文件 |
The domain name is text; the computer needs an IP address to actually reach the server. Turning the domain name into an IP address is the job of the DNS, coming up in 5.1.5.
域名是文字;计算机真正要连上服务器需要的是 IP 地址。把域名转换成 IP 地址是 DNS 的工作,详见 5.1.5。
Try it yourself
动手试试
Take a URL apart
拆解一个 URL
Click each part of this URL to see what it is for.
点击这个 URL 的每一部分,看看它是干什么的。
Explainer · 5.1.3
讲解 · 5.1.3
HTTP and HTTPS
HTTP 与 HTTPS
HTTP (hypertext transfer protocol) is the set of rules for how a web browser and a web server exchange web pages: the browser sends a request, the server sends the page back.
HTTP(超文本传输协议)是网页浏览器与网页服务器交换网页所遵循的规则集合:浏览器发送请求,服务器把网页发回来。
HTTPS (hypertext transfer protocol secure) does the same job, but the data is encrypted. If it is intercepted on the way, it cannot be read.
HTTPS(超文本传输安全协议)做同样的事,但数据是加密的。即使在途中被截获,也读不懂。
| Step in HTTPS | HTTPS 中的步骤 | What happens | 发生了什么 |
|---|---|---|---|
| 1 | 1 | the web server sends the browser its digital certificate (an SSL certificate) to prove it is genuine | 网页服务器把它的数字证书(SSL 证书)发给浏览器,以证明自己是真实的 |
| 2 | 2 | the browser checks the certificate. If it is valid, an encrypted connection is set up | 浏览器检查这份证书。如果有效,就建立一条加密连接 |
| 3 | 3 | all the pages and data now travel encrypted between the browser and the server | 此后所有网页和数据都在浏览器与服务器之间加密传输 |
The web server sends the certificate to the browser, not the other way round. Use HTTPS whenever passwords, payment details or personal data are sent; the padlock in the address bar shows it is in use.
是网页服务器把证书发给浏览器,不是反过来。凡是要发送密码、支付信息或个人数据时,都应使用 HTTPS;地址栏里的锁形图标表示正在使用它。
Explainer · 5.1.4
讲解 · 5.1.4
What a web browser is for
网页浏览器是干什么的
The purpose of a web browser is to retrieve web pages and render the HTML so the pages are displayed for the user. Everything else it does is a function, a feature that helps, not the reason it exists.
网页浏览器的用途是获取网页并渲染其中的 HTML,从而把网页显示给用户看。它做的其他一切都是功能,是提供帮助的特性,而不是它存在的理由。
| Function | 功能 | What it does for the user | 它为用户做什么 |
|---|---|---|---|
| Bookmarks / favourites | 书签 / 收藏夹 | saves the address of a page so it can be reopened without retyping the URL | 保存某个网页的地址,以后重新打开时不用再输入 URL |
| User history | 浏览历史 | keeps a list of pages the user has visited, so they can be found again | 保留用户访问过的网页列表,方便再次找到它们 |
| Multiple tabs | 多标签页 | several pages open at once in one window, each on its own tab | 在一个窗口里同时打开多个网页,每个网页占一个标签页 |
| Storing cookies | 存储 Cookie | keeps the small text files that websites use to recognise the user (see 5.1.6) | 保存网站用来识别用户的小型文本文件(见 5.1.6) |
| Navigation tools | 导航工具 | back, forward, home and refresh buttons for moving between pages | 用于在网页之间移动的后退、前进、主页和刷新按钮 |
| Address bar | 地址栏 | where the user types a URL, or a search term | 用户输入 URL 或搜索词的地方 |
Read whether the question asks for the purpose or the functions. Purpose: render HTML and display web pages. A list of features (bookmarks, tabs, history) answers "functions", not "purpose".
看清楚题目问的是用途还是功能。用途:渲染 HTML 并显示网页。一串特性(书签、标签页、历史)回答的是"功能",不是"用途"。
Try it yourself
动手试试
Purpose or function?
是用途还是功能?
Tap each statement to tag it as the browser's purpose or one of its functions, then check.
点击每条陈述,把它标记为浏览器的用途还是它的一项功能,然后检查。
Explainer · 5.1.5
讲解 · 5.1.5
From a URL to a web page on your screen
从 URL 到屏幕上的网页
This is the sequence markers most want in order. Four things take part: the browser, a DNS (domain name server), the web server, and the page's HTML.
这是考官最看重顺序的一段流程。有四个角色参与:浏览器、一个 DNS(域名服务器)、网页服务器,以及网页的 HTML。
| Step | 步骤 | What happens | 发生了什么 |
|---|---|---|---|
| 1 | 1 | the user enters the URL in the address bar | 用户在地址栏中输入该 URL |
| 2 | 2 | the browser sends the domain name to a DNS | 浏览器把域名发送给一个 DNS |
| 3 | 3 | the DNS looks up the domain name and finds the matching IP address (if this DNS does not have it, the request is passed to another DNS) | DNS 查找该域名,找到对应的 IP 地址(如果这个 DNS 没有,请求会转给另一个 DNS) |
| 4 | 4 | the DNS sends the IP address back to the browser | DNS 把 IP 地址发回给浏览器 |
| 5 | 5 | the browser sends an HTTP or HTTPS request to the web server at that IP address, asking for the page | 浏览器向那个 IP 地址上的网页服务器发送一个 HTTP 或 HTTPS 请求,索要该网页 |
| 6 | 6 | the web server sends the page's files back: the HTML, plus any CSS, images and scripts | 网页服务器把该网页的文件发回来:HTML,以及所有 CSS、图片和脚本 |
| 7 | 7 | the browser renders the HTML and displays the finished page on the screen | 浏览器渲染 HTML,并在屏幕上显示出完整的网页 |
The browser, not the DNS, sends the page request to the web server. The DNS has one job only: turn the domain name into an IP address and return it. Do not say "the DNS requests the page".
向网页服务器发送网页请求的是浏览器,不是 DNS。DNS 只有一个工作:把域名变成 IP 地址并返回。不要说"DNS 去索要网页"。
Try it yourself
动手试试
Follow a page request
跟踪一次网页请求
Step through the seven stages. Watch which part does the requesting at each point.
逐步走完这七个阶段。注意每一步是哪个角色在发出请求。
Explainer · 5.1.6
讲解 · 5.1.6
Cookies
Cookie
A cookie is a small text file that a website asks the browser to store on the user's device. On each later visit to that site, the browser sends the cookie back, so the site can recognise the user or remember their settings.
Cookie 是一个小型文本文件,网站请求浏览器把它保存在用户的设备上。之后每次再访问该网站时,浏览器会把这个 Cookie 发回去,于是网站就能识别出用户、或记住他们的设置。
| Session cookie | 会话 Cookie | Persistent cookie | 持久 Cookie | ||
|---|---|---|---|---|---|
| How long it lasts | 存在多久 | only while the browser is open; removed as soon as the browser is closed | 只在浏览器打开期间;浏览器一关闭就被清除 | kept on the device until it expires or the user deletes it; survives closing the browser | 保存在设备上,直到它过期或被用户删除;关闭浏览器后仍在 |
| Example use | 使用示例 | keeping the contents of an online basket during a single visit | 在一次访问期间保留网上购物篮里的内容 | remembering login details or a language choice so they are not re-entered next time | 记住登录信息或语言选择,下次不用再输入 |
Common uses of a cookie: to save a user's personal details, to keep track of the settings a user prefers, to hold the contents of an online basket, and to remember login details so the user stays signed in.
Cookie 的常见用途:保存用户的个人信息、记住用户偏好的设置、保留网上购物篮里的内容,以及记住登录信息,让用户保持登录状态。
A cookie is a small text file, not a program: it cannot run or carry a virus by itself. Asked what a cookie is, do not answer with a use ("it stores login details"); asked for an example of use, give a real one, not the session-or-persistent definition.
Cookie 是一个小型文本文件,不是程序:它自己不能运行,也不能携带病毒。被问到 Cookie 是什么时,不要用一个用途来回答("它存储登录信息");被要求给使用示例时,给一个真实的例子,而不是会话/持久的定义。
Try it yourself
动手试试
Session or persistent?
会话还是持久?
Tap each statement to tag it as a session cookie or a persistent cookie, then check.
点击每条陈述,把它标记为会话 Cookie 还是持久 Cookie,然后检查。
Check your understanding
自测
What is the purpose of a web browser?
网页浏览器的用途是什么?
Check your understanding
自测
What is the role of the DNS when a user enters a URL?
当用户输入一个 URL 时,DNS 的作用是什么?
Check your understanding
自测
Which cookie is removed as soon as the browser is closed?
哪种 Cookie 会在浏览器一关闭时就被清除?
Common mistakes
常见错误
5.1.1 to 5.1.6
考官针对 5.1.1 至 5.1.6 报告了以下模式
RecurringAsked for the purpose of a web browser, candidates list its functions (bookmarks, tabs, history). The purpose is to render HTML and display web pages. The reverse also happens: functions asked for, purpose given.
反复出现被要求说浏览器的用途时,考生罗列它的功能(书签、标签页、历史)。用途是渲染 HTML 并显示网页。反过来也会发生:问功能,却答用途。
On the DNS, few describe it fully. "The DNS converts the URL to an IP address" just repeats the question. Say how: the browser sends the domain name to the DNS, the DNS looks it up in its records and finds the IP address, and sends that IP address back. And the browser then requests the page from the web server, not the DNS.
关于 DNS,很少有人描述完整。"DNS 把 URL 转换成 IP 地址"只是在重复题目。要说清楚怎么做的:浏览器把域名发给 DNS,DNS 在自己的记录里查找、找到 IP 地址,再把这个 IP 地址发回来。之后是浏览器向网页服务器索要网页,不是 DNS。
On HTTPS, candidates say the browser sends its certificate to the server. It is the other way round: the web server sends its certificate to the browser, which checks it before an encrypted connection is set up.
关于 HTTPS,考生说浏览器把证书发给服务器。其实是反过来:网页服务器把证书发给浏览器,浏览器检查通过后,才建立加密连接。
On cookies, candidates asked what a cookie is answer with a use ("it stores login details"), or identify it only as "a file" without saying a text file. Asked for an example of use, they give the session/persistent definition instead of a real example.
关于 Cookie,被问到Cookie 是什么时,考生用一个用途来回答("它存储登录信息"),或者只说它是"一个文件",没说是文本文件。被要求给使用示例时,他们给出的是会话/持久的定义,而不是一个真实的例子。
Repeats the question: "The DNS changes the URL into an IP address."
重复了题目:"DNS 把 URL 变成 IP 地址。"
Right: "The browser sends the domain name to the DNS. The DNS searches its records for that domain name, finds the matching IP address, and sends the IP address back to the browser."
正确:"浏览器把域名发给 DNS。DNS 在自己的记录里查找该域名,找到对应的 IP 地址,再把 IP 地址发回给浏览器。"
Use, not definition: "A cookie is something that keeps you logged in."
是用途而非定义:"Cookie 是让你保持登录状态的东西。"
Right: "A cookie is a small text file stored on the user's device by the browser at the website's request; it is sent back on later visits so the site can recognise the user."
正确:"Cookie 是浏览器应网站要求保存在用户设备上的一个小型文本文件;以后再访问时会被发回去,让网站能识别出该用户。"
Go deeper
深入练习
Write the URL-to-page sequence from memory
凭记忆写出从 URL 到网页的顺序
From memory, list the seven steps from typing a URL to the page appearing, naming the browser, the DNS, the IP address, the web server and HTML at the right points. Check the order against 5.1.5, and make sure the browser, not the DNS, requests the page.
凭记忆列出从输入 URL 到网页出现的七个步骤,在正确的位置说出浏览器、DNS、IP 地址、网页服务器和 HTML。对照 5.1.5 核对顺序,并确保是浏览器而不是 DNS 在索要网页。
Revision questions
复习题
Past-paper style. Write an answer, then reveal the marking points and mark yourself.
采用历年真题风格。写下答案,然后展开评分要点给自己打分。
[2]State the difference between the internet and the world wide web.
[2]陈述互联网与万维网的区别。
Marking points
评分要点
- The internet is the worldwide infrastructure of interconnected computer networks and the hardware that joins them.
- The world wide web is the collection of websites and web pages that are accessed using the internet.
- 互联网是由相互连接的计算机网络及连接它们的硬件构成的全球性基础设施。
- 万维网是使用互联网访问的网站和网页的集合。
[3]Identify the three parts of the URL https://www.school.edu/timetable.html and state what each part is.
[3]指出 URL https://www.school.edu/timetable.html 的三个部分,并说明每一部分是什么。
Marking points
评分要点
- https is the protocol.
- www.school.edu is the domain name.
- timetable.html is the web page / file name (and path).
- https 是协议。
- www.school.edu 是域名。
- timetable.html 是网页 / 文件名(及路径)。
[6]Describe how a web page is located, retrieved and displayed when a user enters its URL, including the role of the browser, the DNS, IP addresses, the web server and HTML.
[6]描述当用户输入某网页的 URL 时,该网页是如何被定位、获取并显示出来的,包括浏览器、DNS、IP 地址、网页服务器和 HTML 的作用。
Marking points
评分要点
- The browser sends the domain name to a DNS.
- The DNS looks up and returns the IP address of the web server.
- The browser sends an HTTP / HTTPS request to the web server at that IP address.
- The web server sends back the web page, which is written in HTML.
- The browser renders the HTML and displays the page. (The browser, not the DNS, requests the page.)
- 浏览器把域名发给 DNS。
- DNS 查找并返回网页服务器的 IP 地址。
- 浏览器向该 IP 地址的网页服务器发送 HTTP / HTTPS 请求。
- 网页服务器把网页发回,网页用 HTML 编写。
- 浏览器渲染 HTML 并显示页面。(发出页面请求的是浏览器,不是 DNS。)
[3]Explain the difference between HTTP and HTTPS, and describe the role of the digital certificate.
[3]解释 HTTP 与 HTTPS 的区别,并描述数字证书的作用。
Marking points
评分要点
- HTTP is unencrypted; HTTPS encrypts the data that is exchanged, so it cannot be read if it is intercepted.
- Digital certificate: the web server sends its certificate to the browser, which checks it is valid and issued by a trusted authority before an encrypted (SSL / TLS) connection is set up.
- HTTP 不加密;HTTPS 对交换的数据进行加密,即使被拦截也无法读取。
- 数字证书:网页服务器把它的证书发给浏览器,浏览器在建立加密(SSL / TLS)连接之前,检查它是否有效、是否由受信任的机构颁发。
[4]Explain what a cookie is, and give one use of a session cookie and one use of a persistent cookie.
[4]解释 Cookie 是什么,并各举一个会话 Cookie 的用途和一个持久 Cookie 的用途。
Marking points
评分要点
- A cookie is a small text file that a website asks the browser to store on the user's device and that is sent back on later visits.
- Session cookie use: for example holding the items in an online basket during one visit, or keeping the user logged in for that session.
- Persistent cookie use: for example remembering login details or preferred settings between visits.
- Cookie 是网站请求浏览器存放在用户设备上、并在以后访问时被送回的小型文本文件。
- 会话 Cookie 的用途:例如在一次访问中保存网上购物篮里的商品,或在该会话中保持登录。
- 持久 Cookie 的用途:例如在多次访问之间记住登录信息或偏好设置。
Flashcards
记忆卡片
Active recall for this subtopic’s key terms.
针对本子主题关键术语的主动回忆练习。
Keep this subtopic’s practice with you
把这个子主题的练习保存下来
Free account: unlock every revision question and flashcard for 5.1, and every other IGCSE 0478 statement.
免费账户:解锁 5.1 以及所有其他 IGCSE 0478 考纲陈述的全部复习题和记忆卡片。