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In this topic we refer to trials and demos: a trial is limited by time while a demo is limited in features; these can be combined to give a time-limited demo.
Typically, Sheriff-protected applications run in trial or demo mode if there is no valid licence present on the end user's machine.
There are two kinds of time limitation, one is to limit the number of days starting from the date of installation, another is to set an expiry date. With Sheriff you can use Day Metering and/or Expiry Control to make a trial application. Once the trial period has expired and an end user wishes to continue using your application, they will need to extend the demo or obtain a full licence.Demos
Demo applications offer limited features to end users. With Sheriff, a demo application can be a full-featured application yet only allow limited access. With feature access control you can make your demo application more realistic by allowing different users to have access to different levels of features in your application.
Initially, there is the issue of distributing a trial Licence Key. As discussed elsewhere, distribution involves the exchange of a user's Reference Code and the publisher's Licence Key, which can be done via phone calls, faxes, emails or the Web. However, if you do not want to get involved in the distribution of trial Licence Keys you can automate this procedure by calling a couple of Sheriff API functions. The function to issue a licence key without intervention between users and publishers is SLS_License. Challenge is required to call this function otherwise it would be subject to abuse.
Another issue is how to prevent the application from being re-installed after the trial period in the attempt to gain extra time, which can be done by calling SLS_IsProductInstalled. In your application, you need to call SLS_IsProductInstalled before you call SLS_License.
SLS_IsProductInstalled detects whether a specified product has been previously installed, however this does not prevent a product from being installed on another machine.
To prevent users from installing a trial on more than one machine, yet at the same time without the need to manually issue a trial Licence Key, the ideal solution is to set up a Web page to distribute the trial Licence Keys (see topic Sheriff ISR).