1
00:00:00,130 --> 00:00:02,410
So what does it mean to know architectural styles? There

2
00:00:02,410 --> 00:00:06,390
are many many, many architectural styles. So we cannot cover them

3
00:00:06,390 --> 00:00:08,730
all here. What I want to do instead is, I want to

4
00:00:08,730 --> 00:00:10,960
mention a few of those. And then I want to go in

5
00:00:10,960 --> 00:00:13,300
more depth, on one of them. So the first item I

6
00:00:13,300 --> 00:00:17,420
want to mention is pipes and filters. And pipes and filters indicate

7
00:00:17,420 --> 00:00:21,110
an architectural style in which a chain of processing elements, which

8
00:00:21,110 --> 00:00:25,410
can be processes, threads, co-routines, is arranged so that the output

9
00:00:25,410 --> 00:00:28,420
of each element is the input of the next one

10
00:00:28,420 --> 00:00:31,840
and usually with some buffering in between consecutive elements. A

11
00:00:31,840 --> 00:00:34,120
typical example of this, if you're familiar with Unix are

12
00:00:34,120 --> 00:00:37,900
Unix pipes, that you can use to concatenate Unix commands.

13
00:00:37,900 --> 00:00:40,310
Another style I want to mention is the event driven

14
00:00:40,310 --> 00:00:43,540
one. An event driven system typically consists of event

15
00:00:43,540 --> 00:00:46,590
emittors, like the alarm over here, and event consumers, like

16
00:00:46,590 --> 00:00:50,720
the fire truck, down here, and consumers are notified when events

17
00:00:50,720 --> 00:00:53,810
of interest occurr and have the responsibility of reacting

18
00:00:53,810 --> 00:00:56,676
to those events. A typical example will be a GUI,

19
00:00:56,676 --> 00:00:59,950
in which widgets generate events and listeners listen to those

20
00:00:59,950 --> 00:01:02,550
events and react to them. For example, they react to

21
00:01:02,550 --> 00:01:05,060
the push of a button. A very commonly used

22
00:01:05,060 --> 00:01:09,250
architectural style is Publish-subscribe, represented by the paper boy. Over

23
00:01:09,250 --> 00:01:12,420
here. And this is an architectural style in which senders

24
00:01:12,420 --> 00:01:15,870
of messages, they're called publishers, do not send messages directly

25
00:01:15,870 --> 00:01:19,330
to specific recievers. Instead, they publish messages with one

26
00:01:19,330 --> 00:01:22,530
or more associated texts without knowledge of who will

27
00:01:22,530 --> 00:01:26,810
receive such messages. Similarly subscribers will express interest in

28
00:01:26,810 --> 00:01:29,340
one or more tags. And will only receive messages of

29
00:01:29,340 --> 00:01:32,095
interest according to such tags. A typical example of

30
00:01:32,095 --> 00:01:35,240
a publish-subscribe system, will be Twitter. And I'm pretty

31
00:01:35,240 --> 00:01:36,835
sure that most of you are familiar with the

32
00:01:36,835 --> 00:01:41,170
client-server architecture. In which computers in a network, assume one

33
00:01:41,170 --> 00:01:43,930
of two roles. The server provides the resources and

34
00:01:43,930 --> 00:01:47,630
functionality. And the client initiates contact with the server,

35
00:01:47,630 --> 00:01:50,920
and requests the use of those resources and functionality.

36
00:01:50,920 --> 00:01:53,340
Also in this case, a typical example would be

37
00:01:53,340 --> 00:01:56,470
email, in which an email server provides email storage

38
00:01:56,470 --> 00:01:59,390
and management capabilities, and an email client will use

39
00:01:59,390 --> 00:02:02,580
those capabilities. You may also be familiar with peer-to-peer,

40
00:02:02,580 --> 00:02:06,530
or P2P, systems. A P2P system is a type

41
00:02:06,530 --> 00:02:10,850
of decentralized and distributed network system in which individual nodes

42
00:02:10,850 --> 00:02:14,220
in the network, that are called peers, act as independent

43
00:02:14,220 --> 00:02:17,940
agents that are both suppliers and consumers of resources. This

44
00:02:17,940 --> 00:02:20,700
is in contrast to the centralized client-server model, where client

45
00:02:20,700 --> 00:02:23,660
nodes interact with the central authority. And I'm not going to

46
00:02:23,660 --> 00:02:26,030
say anything more about peer-to-peer, because I'm going to show you

47
00:02:26,030 --> 00:02:28,940
two examples, of peer-to-peer systems in the rest of the

48
00:02:28,940 --> 00:02:32,040
lesson. And you probably have at least heard of rest.

49
00:02:32,040 --> 00:02:33,990
Which in this case is not an invitation to

50
00:02:33,990 --> 00:02:36,970
relax as the graphic might indicate. But rather stands for

51
00:02:36,970 --> 00:02:41,400
Representational State Transfer. REST is a hybrid architectural style

52
00:02:41,400 --> 00:02:45,150
for distributed hypermedia systems, that is derived from several other

53
00:02:45,150 --> 00:02:48,210
network based architectural styles. And that is characterized by

54
00:02:48,210 --> 00:02:51,970
uniform connector interface, and even if I'm not going to say

55
00:02:51,970 --> 00:02:54,230
anything else about the rest, I wanted to mention

56
00:02:54,230 --> 00:02:57,440
it, because it is an extremely well known architectural style.

57
00:02:57,440 --> 00:02:59,300
And the reason for this is that REST is

58
00:02:59,300 --> 00:03:03,310
very widely used, because it is basically the architectural style

59
00:03:03,310 --> 00:03:06,050
that governs the world wide web. So we use it

60
00:03:06,050 --> 00:03:08,330
all the time when we browse the internet, for instance.