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ASP.Net allows multiple Web applications to run on the same machine independently of each other. Web applications have their own directory for components (the ".\bin" directory) and its own XML-based configuration file (the ".config" file). This allows us to develop robust applications using custom configurations and components (or different versions of components) for each one.

Each ASP.Net application uses a local assembly cache to hold application specific logic (assemblies, contained in compiled DLLs). The \bin directory located in the application root is the local assembly cache for Web applications. This directory is denied access directly from browsers. This prevents users from downloading or executing any DLLs contained within.

When a Web application is started the .Net Framework constructs a new instance of the System.AppDomain class. When the instance is constructed it creates in-memory shadow copies of the DLLs in the \bin directory. The .Net Framework keeps an in-memory cache (shadow) of all assemblies used so that the actual files (.DLLs) are not locked. The .Net Framework will monitor the original DLL for changes. When changes occur the in-memory cache is updated. Applications already loaded and running with calls in-progress to the old library will continue using the old version so there is no interruption. All new calls to library will be effected, and use the new library. This means that you are free to replace the DLL with new versions as required. Previously with ASP you were required to stop IIS, register the DLL with RegServ32.exe and restart the Web server.

When new libraries are added to the .Net Framework for use in any application system wide, such as the Virtuoso Data Provider, these need to be added to the Global Assembly Cache (GAC). This is achieved using the gacutil.exe utility found in the Framework\[version number] directory. The gacutil.exe tool registers the DLL along with its version. One of .Net's strengths is its ability to maintain multiple versions of DLLs for multiple applications. This prevents "DLL-hell"; new DLLs breaking old applications. Applications can also maintain their own local versions of DLLs in their \bin directory.

gacutil.exe /i <full path and file name>.dll

Registers assemblies with the Global Assembly Cache.

gacutil.exe /l

Can be used to list registered assemblies.

After registering assemblies using the gacutil.exe tool you must add an <add assembly="..." /> entry into the <configuration><system.web><compilation><assemblies> section of the machine.config.

The application given in the previous section can be deployed to Virtuoso in the WebDAV repository or directly on file system under the VSPRoot directory. You should copy the directory structure as defined, applications in the root of the new directory and DLLs in a bin subdirectory. A virtual directory must be configured with execute permissions enabled. The application can be tested with a Web browser.