Web Technologies

1. 00:06Now lets talk about details of the uniform resource identifier. The way how the resources
2. 00:12in the world wide web
3. 00:14are identified. The basic components of the world wide web are
4. 00:20the web documents. Web documents are characterized, also called hypermedia documents,
5. 00:25are characterized by the hyperlinks. Hyperlinks provides the possibility
6. 00:31to point directly to another document.
7. 00:34But what is needed to implement this, is that each of the resources
8. 00:39which are world wide distributed may be uniquely identified
9. 00:46and what's needed and URI provides us is a unique identification scheme
10. 00:53which make it possible to identify each resource in the world wide web.
11. 00:59If we look to our social life then there are two identification models
12. 01:05very popular. The first identification is done by names; each
13. 01:10person has a name and if we talk to each others and we use
14. 01:14the name of the other we can directly
15. 01:17identify our partner by his name. So this is very common it's
16. 01:22used all over the world.
17. 01:25A little problem is there are many persons with the same name, so the name
18. 01:31often does not provide a unique identification.
19. 01:35Besides identifying persons by names, we have the possibility
20. 01:40to identify person by their address.
21. 01:43Addresses are uniquely defined. Addresses are given by
22. 01:49a hierarchical way by defining the country, the city, the
23. 01:53street number, housing unique,
24. 01:56flat of a person. And when we give
25. 02:00his or her address. We can exactly point
26. 02:05a resource to this person.
27. 02:10In the world wide web the identification scheme of URI's the uniform
28. 02:17resource identifier are used.
29. 02:20And exactly like social lives there are two types of such uniform resource identifiers.
30. 02:27There is a possibility to identify as a resources or a web
31. 02:31resources by their name
32. 02:34the scheme is a uniform resource name URN.
33. 02:39Beside of that, there is a possibility to identify resources
34. 02:44by their address and this is done by the uniform resource locator.
35. 02:50This is based on defining the address of a resource, defining the server,
36. 02:57where the resource is stored and then exactly describing the path
37. 03:05the location of the resource at the server.
38. 03:09In the practical application in the world wide web the URL are used.
39. 03:15Only a few exception where
40. 03:17people work with URN for practical application up to now
41. 03:22the URL the uniform resource locators are established.
42. 03:28The advantage is they provide a unique identification
43. 03:32by exactly describing the place where the resource
44. 03:38is stored. The disadvantage is, if address changes, if the resource
45. 03:44is placed on another
46. 03:46server, or if the website is restructured
47. 03:50then this change of address cannot be carried out automatically.
48. 03:58The implementation of the URNs of
49. 04:02the uniform resource name has failed until now due to a lack of a universal
50. 04:08name service.
51. 04:13When we want to access a resource in the world wide web
52. 04:19we have to use our browser and the user can access a resource in the web
53. 04:25via the browser by typing the URI or in most case typing
54. 04:30URL of the resources.
55. 04:33It's also possible to follow a hyperlink
56. 04:36by activating a special designed element
57. 04:40in the text underlined world or an image or video
58. 04:45in the web document which is displayed by the browser,
59. 04:50and then behind there is
60. 04:53a link which leads to the which exactly points to the document
61. 05:00we want to access.
62. 05:02As another way to access a resource in the web we can work
63. 05:09with for example the history directory of our browser or with the bookmark directory.
64. 05:18Directories help to make the
65. 05:22movement in the world wide web more simple and in all cases what's done is
66. 05:28that a resource is requested by giving its URI
67. 05:35in typical way by giving its URL.
68. 05:41What does the requirements for such a uniform resource identifiers?
69. 05:46First requirement is the universality.
70. 05:49So via such a scheme such an identification scheme in the web
71. 05:54it should be possible to address every available resources in the interne,
72. 05:59regardless
73. 06:04of a particular information service
74. 06:07which is used for that resource.
75. 06:11The other requirement for the uniform resource identifier is the uniqueness.
76. 06:17The uniqueness of every resource,
77. 06:21which can be accessed over the web must be uniquely
78. 06:27identifiable, because otherwise the technique does not know which of the
79. 06:34different resources with the same name
80. 06:38should be sent to the browser.
81. 06:42What is also very important
82. 06:44is that such an scheme uniform resource identifier is
83. 06:50extensible so all the new resources that have not been offered until now
84. 06:56should be suitable to be equipped with an identifier.
85. 07:01And it should be fixable.
86. 07:05what does it mean? Typically for example if you have a business card
87. 07:09you want to design also a home page. So in URI should not only be
88. 07:16interchangeable by electronic means it should also be manually
89. 07:22edited.It should be possible to print out for example for business cards.
90. 07:29These are the requirements for such an uniform resource identifier scheme.
91. 07:36Now let's consider the syntax of URI of the uniform resource identifier
92. 07:42that are used to indentified resources of the world wide web.
93. 07:47URIs are standardized by the internet engineering task force and by the
94. 07:54web consortium and it is described in the RFC 1630.
95. 08:02and the syntax of such a URI looks as follows: as a prefix,
96. 08:07then a colon, and then a suffix.
97. 08:11In the prefix the protocol is specified, the protocol all the information service,
98. 08:17is specified over which this resource can be accessed.
99. 08:23And in the suffix there is the place or
100. 08:28the identification specified as the resource can be found.
101. 08:33In the RFC 1630 not only complete URIs are described but also
102. 08:43relative URIs.
103. 08:47According to RFC URIs is either and URL
104. 08:55which specifies the location of resources, or it is specified
105. 09:00by URN which gives as a name of resource.

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