Textbook Reminders Chapter 2

Front 1

Host based server

Back 1

Server performing all four functions. Enabled users to send and received messages. (Terminals). Problems: Must process all messages, slower response time, difficult to upgrade

Front 2

Client based server

Back 2

Personal computers that access stored data. Fundamental problem is, all data must travel to client for processing and more info is transmitted than actually needed.

Front 3

Client Based architectures

Back 3

Load is split. Client side does presentation logic, while server side does data access logic and data storage. Enables software and hardware from different vendors to be used together.

Front 4

Middleware

Back 4

Software that sites between software on the client and the application software on the server

Two functions: provides standard way of communicating that can translated b/ software from diff vendors

manage the message transfer from clients to servers (vice versa) so that client need not know the specific server that contains the application's data. Application sends msgs to middleware which is then forwarded to correct server.

Front 5

Two Tier Architecture

Back 5

Server is responsible for the data and the client, the application and presentation. Only uses two sets of computers, one set of clients and one set of servers.

Front 6

Three Tier architecture

Back 6

Three sets of computers. Software on client computer is responsible for presentation, logic, an application server is responsible for application, logic and a separate database server is responsible for data access logic and data storage.

Front 7

N-Tier architecture

Back 7

More than three sets. the clientis responsible for presentation logic, a database server is responsible for the data accesslogic and data storage, and the application logic is spread across two or more differentsets of servers. Advantage is it separates theprocessing that occurs to better balance the load on the different servers; it is morescalable. BUT it puts greater load on server and is also more difficult to program and test.

Front 8

Thin Client

Back 8

Places little or no application logic on the client. Easier to manage, only server needs to be updated. Thin-client architectures are the future. More and more application systems arebeing written to use a Web browser as the client software.

Front 9

Thick Client

Back 9

Places all or almost all application logic on the client, software on all client needs to be updated.. can be a burden.

Front 10

Hypertext Transfer Protocol (HTTP)

Back 10

Standard protocol for communication b/ a Web browser and a Web server. To get a page from a Web server, the Webbrowser issues a special packet called an HTTP request that contains the URL and otherinformation about the Web page requested. Once the server receives theHTTP request, it processes it and sends back an HTTP response, which will be therequested page or an error message.

Front 11

Hypertext Markup Language (HTML)

Front 12

Uniform resource locator (URL)

Back 12

specifies the Internet address of the Web server and thedirectory and name of the specific page wanted. If no directory and page are specified,the Web server will provide whatever page has been defined as the site’s home page.

Front 13

How does http get a web page?

Back 13

To get a page from a Web server, the Webbrowser issues a special packet called an HTTP request that contains the URL and otherinformation about the Web page requested. Once the server receives theHTTP request, it processes it and sends back an HTTP response, which will be therequested page or an error message.

Front 14

Requesting a page with graphic images

Back 14

In this case, there would be three request-response pairs.First, the browser would issue a request for the Web page, and the server would send theresponse. Then, the browser would begin displaying the Web page and notice the twographic files. The browser would then send a request for the first graphic and a requestfor the second graphic, and the server would reply with two separate HTTP responses,one for each request.

Front 15

HTTP request from a Web browser to a Web server has three parts

Back 15

Request Line. Request Header. Request Body.

Front 16

Request Line

Back 16

which starts with a command (e.g., get), provides the Web pageand ends with the HTTP version number that the browser understands; the version number ensures that the Web server does not attempt to use a more advanced ornewer version of the HTTP standard that the browser does not understand.

Front 17

Request Header

Back 17

which contains a variety of optional information such as theWeb browser being used (e.g., Internet Explorer) and the date.

Front 18

Request Body

Back 18

which contains information sent to the server, such as informationthat the user has typed into a form.

Front 19

HTTP response 3 steps

Back 19

Response Status. Response Header. Response Body

Front 20

Response Status

Back 20

which contains the HTTP version number the server hasused, a status code (e.g., 200 means “okay”; 404 means “not found”), and a reasonphrase (a text description of the status code).

Front 21

Response Header

Back 21

which contains a variety of optional information, such asthe Web server being used (e.g., Apache), the date, and the exact URL of the pagein the response.

Front 22

Response Body

Back 22

which is the Web page itself.