Chapter 1. Basic Concepts
Table of Contents
Objectives .................................................................................................................................................................... 2
1.1 Introduction ...................................................................................................................................................... 2
1.2 Hypertext .......................................................................................................................................................... 2
1.2.1 Anchors and Links ............................................................................................................................. 3
1.2.2 Jumps ................................................................................................................................................. 3
1.2.3 Knowledge Additivity........................................................................................................................ 4
1.2.4 Chain of Links ................................................................................................................................... 4
1.2.5 Loops and Mesh ................................................................................................................................. 4
1.2.6 Hypermedia........................................................................................................................................ 4
1.2.7 Authoring Hypertext .......................................................................................................................... 4
1.2.8 Getting lost in 'hyperspace' ................................................................................................................ 5
1.3 The Ultimate Hypermedia System: The World Wide Web .............................................................................. 5
1.3.1 Basic Ideas of the Web ..................................................................................................................... 5
1.3.2 Fields of Application ......................................................................................................................... 6
1.3.3 The Web as a Digital Library............................................................................................................. 6
1.4 Summary of Web Terminologies ...................................................................................................................... 7
1.4.1 Network Protocols ............................................................................................................................. 7
1.4.2 Web Application (Webapp) ............................................................................................................... 7
1.4.3 Uniform Resource Locator (URL) ..................................................................................................... 8
1.4.4 HyperText Markup Language (HTML) ............................................................................................. 8
1.4.5 HyperText Transfer Protocol (HTTP)................................................................................................ 8
1.5 The Client-server Computing Model ................................................................................................................ 9
1.5.1 A Definition and some History .......................................................................................................... 9
1.5.2 Functionality .................................................................................................................................... 10
1.5.3 Information and Processing on the Web .......................................................................................... 11
1.5.4 MIME Types .................................................................................................................................... 11
1.5.5 Web Servers ..................................................................................................................................... 12
1.5.6 Distributed Processing ..................................................................................................................... 13
1.6 Review Questions ........................................................................................................................................... 14
1.7 Answers to Exercises ...................................................................................................................................... 15
1.7.1 Exercise 2......................................................................................................................................... 15
1.7.2 Exercise 3......................................................................................................................................... 16
1.7.3 Exercise 4......................................................................................................................................... 16
1.7.4 Exercise 5......................................................................................................................................... 16
1.7.5 Exercise 6......................................................................................................................................... 17
1.7.6 Review Question 1 ........................................................................................................................... 17
1.7.7 Review Question 2 ........................................................................................................................... 17
1.7.8 Review Question 3 ........................................................................................................................... 17
1.7.9 Review Question 4 ........................................................................................................................... 17
1.7.10 Review Question 5 ........................................................................................................................... 17
1.7.11 Review Question 6 ........................................................................................................................... 18
, Basic Concepts
Objectives
At the end of this chapter you will be able to:
• Explain the basics of Hypertext;
• Explain web technology terminologies;
• Understand the client-server computing model.
1.1 Introduction
In 2009 the Internet celebrated its 40th anniversary, and the World Wide Web had been in existence for over 15 years.
The concepts of computer networks and hypertext on which these technologies rely are only a little older. And yet
the speed of development of these technologies, the speed of uptake by companies, and the speed of acceptance by
consumers is unlike anything mankind has witnessed. Although both the Internet and the Web are firmly rooted in
academic, altruistic endeavour, there is no doubt that the commercial interests are currently driving much of the
technological development. This module aims to prepare you for contributing to this endeavour by helping you to
understand the basic ideas and technologies behind the Internet, and giving you the opportunity to design and write
Web pages using HTML5 and JavaScript.
The module starts here with, inevitably, the more theoretical aspects of the Internet and the Web. We begin by
explaining hypertext before moving on to the most elaborate hypermedia system, the Web, and the ideas of client-
server computing that allow us to use it.
1.2 Hypertext
Take a dictionary and observe how its content is linked together. How do you search for the meaning of a word? How
can you find another word synonymous with that word? The dictionary is a paper example of a hypertext system. So
are encyclopedias, product catalogues, user help books, technical documentation and many other kinds of books.
Information is obtained by searching through some kind of index - the dictionary is arranged in alphabetical order,
and each word is its own index. Readers are then pointed to the page of any other related information. They can read
the information they are interested in without having to read the document sequentially from beginning to end.
Hypertext systems allow for non-sequential or non-linear reading. This is the underlying idea of a hypertext system.
The result is a multidimensional document that can be read by following different paths through it. In this section we
will look into the application of hypertext in computer systems, mainly the World Wide Web hypertext system.
The main use of hypertext is in information retrieval applications. The ease of linking different pieces (fragments) of
information is the important aspect of hypertext information retrieval. The information can be of various media: it
may be fragments of textual documents, structured data from databases, or list of terms and their definitions. Any of
these, or a mixture thereof, can make up the contents of a hypertext document.
Therefore, in a hypertext system it is possible to:
• link with a term that represents aspects of the content of a document;
• connect two related documents;
• relate a term to a fragment containing its definition and use; and
• link two related terms.
Such a hypertext system can store a large collection of textual and multimedia documents. Such a hypertext system
gives the end-user access to a large repository of knowledge for reading, browsing and retrieving. This is a "database"
of sorts, and is the reason why such a hypertext system is called a digital library. The Web started as an extensively
large digital library. As it has grown in popularity, it has offered the possibility of interactive applications and
commerce on the Internet, making it much more than a digital library.
To do
Read about networked hypertext and hypermedia in your textbooks.
We now explain some basic concepts on the use of hypertext.
2
, Basic Concepts
1.2.1 Anchors and Links
A hypertext document contains links referring to other parts of the document, or even to whole other documents. A
hypertext document does not have to be read serially; the fragments of information can be accessed directly via the
links contained in the document.
The links embedded in a document are known as hyperlinks. When selected, these hyperlinks allow for the portion
of the document linked to by the hyperlink to be displayed. This allows the reader to jump to another part of the same
page, another page in the same document, or another document. By following a series of hyperlinks, the reader can
follow their own path through the document.
A computerised hypertext system implements this idea by including anchors and links in documents, which are
usually represented by files. An anchor is a fragment of information which links to another document or portion
thereof. It is the visual representation of a link. A link is the actual reference (or "pointer") to the other document. For
example, in Figure 1 the fragment of Document A containing 'You can find this in Section 5 of B' is an anchor from
which there is a link to the relevant section in Document B.
Figure 1: Illustration of Anchor and Link
Take care not to confuse anchor or link. A link is a pointer to another piece of information within the same document
or in another document; often you cannot see how that link is implemented (it may be a hidden URL or some other
programmed mechanism). An anchor is a fragment of information which the user interacts with in order to access the
link. For instance, in a Web Browser the phrase "Click here to return to the previous page" is the anchor which the
user interacts with — it contains the link to the previous page.
A hyperlink must have unambiguous reference to the document: this is usually information on the document's location
(where in some file space or network it is) and the mechanism to access it (called the communication protocol). In
Chapter 3 you will be introduced to HTML anchors and how the referenced documents are identified and located
with URLs.
1.2.2 Jumps
A hypertext document allows links to portions of the document occurring before the link's anchor. This allows the
reader to loop to portions of the document that they have already seen.
The table of contents at the beginning of this chapter is a collection of anchors with explicit links to the internal parts
of the chapter. A book’s bibliography is another collection of links but it refers to external information. To refer to
the internal parts of this chapter is simple: the reader can merely turn to the appropriate page, identified by page
number. However, referring to the external information given in a bibliography requires a more complicated effort of
searching.
In computer-based hypertext documents, the mechanism to follow a link (the jump) is automatic. Jumping to an
external link (another document) is as easy as jumping to an internal link within the same document. As long as the
link is sufficiently specified with the name and the exact location of the linked document, the user can directly access
the linked document with a simple click on the anchor.
3
Table of Contents
Objectives .................................................................................................................................................................... 2
1.1 Introduction ...................................................................................................................................................... 2
1.2 Hypertext .......................................................................................................................................................... 2
1.2.1 Anchors and Links ............................................................................................................................. 3
1.2.2 Jumps ................................................................................................................................................. 3
1.2.3 Knowledge Additivity........................................................................................................................ 4
1.2.4 Chain of Links ................................................................................................................................... 4
1.2.5 Loops and Mesh ................................................................................................................................. 4
1.2.6 Hypermedia........................................................................................................................................ 4
1.2.7 Authoring Hypertext .......................................................................................................................... 4
1.2.8 Getting lost in 'hyperspace' ................................................................................................................ 5
1.3 The Ultimate Hypermedia System: The World Wide Web .............................................................................. 5
1.3.1 Basic Ideas of the Web ..................................................................................................................... 5
1.3.2 Fields of Application ......................................................................................................................... 6
1.3.3 The Web as a Digital Library............................................................................................................. 6
1.4 Summary of Web Terminologies ...................................................................................................................... 7
1.4.1 Network Protocols ............................................................................................................................. 7
1.4.2 Web Application (Webapp) ............................................................................................................... 7
1.4.3 Uniform Resource Locator (URL) ..................................................................................................... 8
1.4.4 HyperText Markup Language (HTML) ............................................................................................. 8
1.4.5 HyperText Transfer Protocol (HTTP)................................................................................................ 8
1.5 The Client-server Computing Model ................................................................................................................ 9
1.5.1 A Definition and some History .......................................................................................................... 9
1.5.2 Functionality .................................................................................................................................... 10
1.5.3 Information and Processing on the Web .......................................................................................... 11
1.5.4 MIME Types .................................................................................................................................... 11
1.5.5 Web Servers ..................................................................................................................................... 12
1.5.6 Distributed Processing ..................................................................................................................... 13
1.6 Review Questions ........................................................................................................................................... 14
1.7 Answers to Exercises ...................................................................................................................................... 15
1.7.1 Exercise 2......................................................................................................................................... 15
1.7.2 Exercise 3......................................................................................................................................... 16
1.7.3 Exercise 4......................................................................................................................................... 16
1.7.4 Exercise 5......................................................................................................................................... 16
1.7.5 Exercise 6......................................................................................................................................... 17
1.7.6 Review Question 1 ........................................................................................................................... 17
1.7.7 Review Question 2 ........................................................................................................................... 17
1.7.8 Review Question 3 ........................................................................................................................... 17
1.7.9 Review Question 4 ........................................................................................................................... 17
1.7.10 Review Question 5 ........................................................................................................................... 17
1.7.11 Review Question 6 ........................................................................................................................... 18
, Basic Concepts
Objectives
At the end of this chapter you will be able to:
• Explain the basics of Hypertext;
• Explain web technology terminologies;
• Understand the client-server computing model.
1.1 Introduction
In 2009 the Internet celebrated its 40th anniversary, and the World Wide Web had been in existence for over 15 years.
The concepts of computer networks and hypertext on which these technologies rely are only a little older. And yet
the speed of development of these technologies, the speed of uptake by companies, and the speed of acceptance by
consumers is unlike anything mankind has witnessed. Although both the Internet and the Web are firmly rooted in
academic, altruistic endeavour, there is no doubt that the commercial interests are currently driving much of the
technological development. This module aims to prepare you for contributing to this endeavour by helping you to
understand the basic ideas and technologies behind the Internet, and giving you the opportunity to design and write
Web pages using HTML5 and JavaScript.
The module starts here with, inevitably, the more theoretical aspects of the Internet and the Web. We begin by
explaining hypertext before moving on to the most elaborate hypermedia system, the Web, and the ideas of client-
server computing that allow us to use it.
1.2 Hypertext
Take a dictionary and observe how its content is linked together. How do you search for the meaning of a word? How
can you find another word synonymous with that word? The dictionary is a paper example of a hypertext system. So
are encyclopedias, product catalogues, user help books, technical documentation and many other kinds of books.
Information is obtained by searching through some kind of index - the dictionary is arranged in alphabetical order,
and each word is its own index. Readers are then pointed to the page of any other related information. They can read
the information they are interested in without having to read the document sequentially from beginning to end.
Hypertext systems allow for non-sequential or non-linear reading. This is the underlying idea of a hypertext system.
The result is a multidimensional document that can be read by following different paths through it. In this section we
will look into the application of hypertext in computer systems, mainly the World Wide Web hypertext system.
The main use of hypertext is in information retrieval applications. The ease of linking different pieces (fragments) of
information is the important aspect of hypertext information retrieval. The information can be of various media: it
may be fragments of textual documents, structured data from databases, or list of terms and their definitions. Any of
these, or a mixture thereof, can make up the contents of a hypertext document.
Therefore, in a hypertext system it is possible to:
• link with a term that represents aspects of the content of a document;
• connect two related documents;
• relate a term to a fragment containing its definition and use; and
• link two related terms.
Such a hypertext system can store a large collection of textual and multimedia documents. Such a hypertext system
gives the end-user access to a large repository of knowledge for reading, browsing and retrieving. This is a "database"
of sorts, and is the reason why such a hypertext system is called a digital library. The Web started as an extensively
large digital library. As it has grown in popularity, it has offered the possibility of interactive applications and
commerce on the Internet, making it much more than a digital library.
To do
Read about networked hypertext and hypermedia in your textbooks.
We now explain some basic concepts on the use of hypertext.
2
, Basic Concepts
1.2.1 Anchors and Links
A hypertext document contains links referring to other parts of the document, or even to whole other documents. A
hypertext document does not have to be read serially; the fragments of information can be accessed directly via the
links contained in the document.
The links embedded in a document are known as hyperlinks. When selected, these hyperlinks allow for the portion
of the document linked to by the hyperlink to be displayed. This allows the reader to jump to another part of the same
page, another page in the same document, or another document. By following a series of hyperlinks, the reader can
follow their own path through the document.
A computerised hypertext system implements this idea by including anchors and links in documents, which are
usually represented by files. An anchor is a fragment of information which links to another document or portion
thereof. It is the visual representation of a link. A link is the actual reference (or "pointer") to the other document. For
example, in Figure 1 the fragment of Document A containing 'You can find this in Section 5 of B' is an anchor from
which there is a link to the relevant section in Document B.
Figure 1: Illustration of Anchor and Link
Take care not to confuse anchor or link. A link is a pointer to another piece of information within the same document
or in another document; often you cannot see how that link is implemented (it may be a hidden URL or some other
programmed mechanism). An anchor is a fragment of information which the user interacts with in order to access the
link. For instance, in a Web Browser the phrase "Click here to return to the previous page" is the anchor which the
user interacts with — it contains the link to the previous page.
A hyperlink must have unambiguous reference to the document: this is usually information on the document's location
(where in some file space or network it is) and the mechanism to access it (called the communication protocol). In
Chapter 3 you will be introduced to HTML anchors and how the referenced documents are identified and located
with URLs.
1.2.2 Jumps
A hypertext document allows links to portions of the document occurring before the link's anchor. This allows the
reader to loop to portions of the document that they have already seen.
The table of contents at the beginning of this chapter is a collection of anchors with explicit links to the internal parts
of the chapter. A book’s bibliography is another collection of links but it refers to external information. To refer to
the internal parts of this chapter is simple: the reader can merely turn to the appropriate page, identified by page
number. However, referring to the external information given in a bibliography requires a more complicated effort of
searching.
In computer-based hypertext documents, the mechanism to follow a link (the jump) is automatic. Jumping to an
external link (another document) is as easy as jumping to an internal link within the same document. As long as the
link is sufficiently specified with the name and the exact location of the linked document, the user can directly access
the linked document with a simple click on the anchor.
3
