MAINTAINING STATE IN A STATELESS SYSTEM

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Lesson 19

MAINTAINING STATE IN A STATELESS SYSTEM

You know that http is stateless. Another reason why we need to write scripts or develop our back end is

that we want to maintain state. In other words, we want to link different clicks/steps involved in an e-

commerce transaction. When we go to an ecommerce site, we are generally asked to take three different

steps, that is, provide Registration information, and make selection of items (Add to Cart) and Confirm

Order. The question is how do we create link or maintain state among these different steps. There are

following options available for programmers in this regard:

A temporary file may be created on the server side and we code our scripts behind the steps/clicks -

temporary file using the same common ID. At the end our confirm order script puts this information in

some database using insert query.

Another method is to use the client side or cookies for maintaining state. Information regarding

Registration and Add to Cart can be stored in cookies and at Confirm Order cookies against these URLs

would revert to the serve side and be stored in databases against a common ID.

We can also use hidden forms' fields. We keep data back and forth within forms to maintain state.

Following is a piece of HTML code for a form (Add to cart) in which hidden fields are used. I have used

pairs of input tags with type hidden and type checkboxes. (I can also use them in a For loop using

Recordset object of ASP then it would be possible that these pairs of input tags are generated in a loop and

information of records available in databases is directly picked up and printed for me). Because of type

hidden the item name and item code/value for each item would be there in the form against each item but

would remain hidden. When the user selects items (through check boxes) and presses Add to Cart his

selected information would go to some script which would be coded such that it would open a new page

with button Confirm Order. In this new form the item code or value of selected items would be present but

would remain hidden. When a user presses the button Confirm Order the information of selected items is

stored in the databases (through a script) against the item code present in the form, though hidden. We can

say that state is maintained here between steps Add to Cart and Confirm Order in the sense that selections

made in step Add to Cart were passed over or provided to the next step Confirm Order.

Example - Hidden Fields

<FORM NAME="Form1"> <INPUT TYPE= "HIDDEN" NAME= "Shirt1" VALUE="25"> <INPUT

TYPE= "CHECKBOX" NAME= "Check1">Blue Cotton Shirt <br> <INPUT TYPE= "HIDDEN"

NAME= "Shirt2" VALUE="26"> <INPUT TYPE= "CHECKBOX" NAME= "Check2" >Green Cotton

Shirt <br>

<INPUT TYPE= "HIDDEN" NAME= "Shirt3" VALUE="27"> <INPUT TYPE= "CHECKBOX"

NAME= "Check3">White Silk Shirt ....

<P>

<INPUT TYPE="submit" NAME="Go" VALUE="Register!"> <INPUT TYPE="RESET"

VALUE="Reset!"></FORM>

Another option is to keep everything in databases. Here, information of each step is recorded in appropriate

tables of a database itself and linked up with the help of a commonID. It is relatively more costly and time

consuming option.

We can use Servlets to write our scripts to speed up processing. It gets tricky, as one must have a solid

knowledge of programming to implement these methods. Here, the idea is just to give you a broad

concept/picture as to how the state is maintained.

Client server architecture

Note that we may have different tiers in client server architecture depending on where the processing of

data takes place. In 1-tier architecture, the entire processing takes place at a single place/zone. For example,

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in Fig. 1 below, the processing of data only takes place in the main frame and different machines are

attached to it just as display terminals. Conversely, the entire processing may take place at individual

terminals and a centralized machine called file server just stores the files having no role in the processing of

data. Again, that would be an example of 1-tier architecture (Fig. 2). Example of 2-tier architecture is where

processing of HTML code takes place on the client side and the web page request is processed on the server

side (Fig. 3). In a 3-tier architecture, we can place our database management system or application software

on a different processing zone or tier than the web server (Fig. 4). Similarly in a 4-tier architecture ,for

example, we can place the payment processing system at the 4th tier. Thus, we can divide the client server

architecture into n tiers.

Fig. 1

Fig. 2

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Fig. 3

Fig. 4

Web server

You know that web server is a machine that serves up the web page requests of a client on the internet. It is

a combination of hardware and software. Decision as regards the type of a web server is largely dependent

on the volume and type of web activities. So, transaction processing sites generating dynamic pages with

high traffic volumes would need web server software that is more efficient and can easily be upgraded.

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Operating systems for web servers

A computer must have an operating system to run programs. It also provides input and output services to

devices connected to a computer such as monitor, printer etc. Commonly used web server operating

systems are Microsoft Windows NT Server, Microsoft Windows 2000 Advanced Server, Microsoft.NET

Server, Linux or Unix based operating systems such as Solaris. Unix-based web servers are more popular

and are considered to be more secured. Linux is open source operating system which is fast, efficient and

easy to install. Open source software is developed by a community of programmers who make it available

for download at no cost. Web Server Software Common examples of web server software are Apache

HTTP server, MS Internet Information Server (IIS) and Sun ONE web server. Apache is open source code

developed in 1994. Today, it dominates the web, because it is free and performs very efficiently. IIS comes

with MS windows 2000 and NT operating systems. IIS's inclusion of ASP provides an environment in

which HTML pages and scripts can be combined to produce dynamic web pages. Sun one (iPlanet or

Netscape) web server is a joint product of AOL and Sun Microsystems. It can run on many operating

systems including Solaris and Windows. Web Server Hardware Web Server computers have generally more

memory. They have larger and faster hard disk drives and faster processors than the typical desktop PCs.

Companies that sell web server hardware such as Dell, Hewlett Packard etc. all have configuration tools on

their web sites that allow visitors to design their own web servers.

Performance of web sever

Performance of web servers can be evaluated mainly on the basis of two factors:

Throughput, which is the number of http requests that a particular server hardware and

software can handle in the unit time; and

Response time, which is the amount of time a web server requires to process one request.

Web server hardware architectures

We can divide e-commerce sites up to n-tier architectures. Some web sites are so large that we need more

than one computer within each tier. For sites which have to deliver millions of individual pages and process

thousand of customer and vendor transactions each day, site administrators must plan carefully how to

configure their web server computers. They may adopt two different approaches in this regard. They can

use centralized architecture approach where they can use few but very fast and large computers within each

tier; or they may adopt decentralized approach using many less powerful computers and dividing workload

among them. Web hosting choices ISPs also offer web hosting arrangements.

Shared hosting means that a client's web site is hosted on a server that simultaneously hosts other web sites

and is operated by an ISP through its location.

In Dedicated hosting a web server is arranged by the ISP for a client but that client does not share it with

other clients of the ISP. In both cases ISP owns the hardware but leases it to the client and is responsible

for its maintenance. In Co-location hosting, the ISP offers on rent a physical space to client to install its

own server hardware and software and maintain it by itself. Companies may opt to run a server in house

which is called self hosting.

E-commerce software

Size and objectives of e-commerce sites vary thus variety of software and hardware products are developed

which can be used to build those sites. Type of e-commerce software that an organization needs depends

on several factors. Typically all e-commerce software must at least provide:

A catalog display

Shopping cart capabilities

Transaction processing

Large or complex e-commerce sites also use software that adds other features and capabilities as follows:

Middleware

Application integration

Web services

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Integration with ERP Software

Supply chain management software

Customer Relationship Management (CRM) Software

Content Management Software

Knowledge Management Software

Catalog display

A Static catalog is a simple list written in HTML. One has to edit the HTML code to change it. A dynamic

catalog stores information about items in a database usually on a different computer accessible by the web

server. It can provide photos, detailed description and search facility about the availability of items.

Shopping cart

In early days form based shopping cart was used wherein the user had to remember and type certain

information. It is now replaced by electronic shopping cart/basket that keeps record of the items the

customer has selected and allows customers to view the details of the items selected. The customer can add

new items or remove items. To order an item, a customer simply clicks at that item option. All details of an

item, including its price, product no. and order identifying information are stored automatically in the cart.

Transaction processing

It occurs when a customer clicks at checkout or confirm order button and is subjected to some payment

processing mechanism. It represents the most complex part of online sale. Calculation of taxes, shipping

costs etc. is important parts of this process. Some software enables a web server to obtain updated shipping

rates by directly connecting to shipping companies' web sites.

Advanced functions of e-commerce software

Middleware

Large companies establish connections between their e-commerce software and their existing accounting

system by using a type of software called Middleware which is a part of e-commerce software package.

Application integration

A program that performs a specific function such as creating invoices/bills or processing payment received

from customers is called an application program. We know that Database Management Software stores

information in a structured way. Experts should properly consider that their e-commerce software

application programs must be compatible and fully integrated with the Database Management Software.

For example if a company has existing inventory database then the experts should select that e-commerce

application program that supports such a system.

Web Services

Web services are defined as a combination of software tools that allow application software in one

organization communicate with other programs/applications over a network by using a specific set of

standard protocols. For example a company that wants to gather all its financial management information in

one spreadsheet can use web services to automatically get bank account details, information about loans,

stock value etc. from different independent sources. Similarly, web services can be used to obtain price and

delivery information about goods from different vendors/suppliers, review this information, place the order

to the right vendor/supplier and track the order till shipment is received.

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