The Web, a network of networks, requires its own set of standards. One computer network will have different hardware, operating systems, and means of internal communication from another. Yet both may be part of the world wide web. How do they communicate? With protocols defined externally from each network.
- Hypertext Markup Language – major features
This would display the text “go somewhere else”. Clicking on the text would take you to another web page, the web page at www.anotherpage.com.
HTML includes formatting statements.
- Print the next part <italics> in italics </italics>
- Note the slash means turn off the feature.
HTML – some features are visual, some are semantic, e.g.
- <italic> – is visual
- <strong> – is semantic (use “something” which shows text should be emphasized)
Controversy over semantic vs visual
- “content is king” people favor semantic
- Business and advertising people favor visual
Major issue with HTML protocol – mostly one way. Information transmitted back to server is limited. This makes it difficult to write code which is “persistent”. An example of a persistent application is a shopping cart, where the shopping cart site, e.g. Amazon remembers you and remembers what you have in your cart.
Cascading Style Sheets
- Separate style from content
- Style sheets can be defined in line with the content or in a separate file
- See different style sheets used with the same content at:
- The idea at the above website is you click on the various style sheets to observe the way CSS can make the same content look very different.
- The important thing to learn about zen garden is that all the different versions of the site look the same to a search engine. All the same text – only the style is different.
Universal Data Standard – XML
Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards.
The design goals of XML emphasize simplicity, generality, and usability over the Internet. It is a textual data format with strong support via Unicode for the languages of the world. Although the design of XML focuses on documents, it is widely used for the representation of arbitrary data structures, for example in web services.
Many application programming interfaces (APIs) have been developed to aid software developers with processing XML data, and several schema systems exist to aid in the definition of XML-based languages.
Extended Markup Language
- Looks like this:
- <standard>Medical Record #1234 4/1/2010</standard><name>Brian Gulino</name><address>1152 Stratford Drive</address> . (and so on)
- Allows records to be universal and interoperable
- XML is used to develop universal document standards for things like medical records or criminal records so large agencies can use it to exchange information. It is also used on a smaller scale, simply to put data in a more readable format.
Mail Protocols and Security
Simple mail transfer protocol – symmetric – machine to machine
- You use it to send your mail
- Your mail service provider uses it to send and receive mail
- You use POP3 to receive mail
Post office protocol
- Runs on port 110
- You use it to get mail.
- SMTP and POP3 are used to send and receive mail and the mail goes away from the sending machine – “just like real mail”
- Major difference – IMAP saves the mail on the server – sends a copy of the mail.
- Needed with multiple devices.l
- Text only – no images, no fancy formatting
- Email addresses are all interpreted as lower case
- acts like real mail
- very universal
- set up so people could get mail in more than place
- IMAPP will duplicate folder structure on clients
- Mail stored on external server
- Implications of external mail storage
You have no control over your mail
A real life illustration of IMAP and servers is here: