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Ensure systems are dependable – Scalability, availability and security are not optional. Extending business-critical applications to the Web doesn’t make them any less critical. In a system that is only available 95% of the time, 5% of sales transactions are lost.
What is it meant by ‘extending’ here?
May 15th, 2011 
admin 
Posted in web application security
‘Extending’ in this case refers to adding these applications to Web use, where before they were used in a more limited way (probably internally only).
In the context you mention, if a business extends its critical applications to the Web, the business is making those applications available via the Web.
As Momomo said, it means “making them available through the web.”
The point here is that when you make a business-critical non-web application, such as payroll or an in-store sales application, available over the Web (Internet or Intranet), you add another layer of complexity. Not only do you have to keep the application server up 24/7, but the also the network server that allow you to GET to the application server. It’s still a business-critical application, so now the network server ALSO has be up 24/7. Just because the application is now available on the Web doesn’t make it any less critical.