ALP Compatibility and limitations
This page contains summary information about ALP compatibility and limitations. In the reference pages you will find more details on the particular problems. See the ALP examples too.

OS compatibility

ALP engine (i.e. core plus the ALP run-time library) runs on the consumer Windows platforms beginning with Windows 95 (with IE4) and on the business Windows platforms beginning with Windows NT 4.0 (with IE4 installed). There is nothing to prevent ALP from running on any future Windows version, it is currently tested on all the available Windows OS versions up to Windows 2003.

Required additional components are always installed with Microsoft Internet Explorer 4 or later (this mostly causes NT4 that has older version pre-installed).

Technology compatibility and limitations

Standard simple generators: DirList, RawSpool, SimpleTemplate have no special requirements. In order to limit memory requirements by default ALP limits transferred content of one response to 1MB. It can be changed through the configuration. When the target resource is a file that must be "downloaded" it is recommended to generate file: protocol links instead of the alp: links because Internet Explorer treats them in special manner and thus avoids unnecessary copy and buffering operations - feature not available for the other protocols. Of course if the content is generated alp: protocol should be used and if the size of the generated resource is bigger than the default limit site should be configured with a bigger limit. Note that most of the ActiveX (embeded in a page) and file downloads require cache files. 

GateCGI native application executes CGI applications/scripts. It is limited by the CCGA assumption to request parameters in form paramname=value&...&paramnameN=valueN. The CGI applications that do not support this form are not supported. Some of these applications are still able to work using some tricks. This query string parameter form become an implicit standard in the last years and major part of applications support it. ALP passes fictitious values for the environment variables where the corresponding information is not available because of the desktop nature of the ALP. For example host name is the site root directory full path. Developers should check if their applications will work properly in this situation. The environment parameters not related to the network settings are passed correctly. GateCGI is limited to execution of the Win32 CGI applications - DOS applications are not supported.

ScriptGen native application supports ASP compatible pages and raw scripts. The same notes about the environment variables are true as for the CGI applications. ScriptGen object model provides utility function MapPath that should be used to map URL to a local path.

The ASP compatible pages are portable to the server side classic ASP provided by the Microsoft IIS 4.0 or later. ASP developers should take care to not use some of the extended collection features available in ALP, but not available in the classic ASP when portability is a requirement..

There is a set of features available on IIS that can not be emulated or integrated on the client side without adding more strict requirements. These features include integrated transactions support and all features related to a software that is not always available or properly configured on the client desktops. These features are not planned to become a standard part of the ALP, but custom versions can be developed if our customers are interested in such features for their internal corporate software.

All features available through a standard usage of ActiveX components in the scripts are available for the ALP ASP compatible pages (ADO, Scripting library and so on) . Note that Server.CreateObject method supports creation of the components not only by progID but also by CLSID passed as string. But please don't forget that ALP application you wrote will run on other desktops - you will need to provide with your application re-distributable files of the components you use - if you know they are not available by default on the target machines.

ALP is not binary compatible with the special type of ASP components that use the environment objects directly (ASP Objects). The ASP objects must use IDispatch to access the ASP object model in order to run on both ALP and IIS. See ALP Objects for more information.

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