Creating OpenACS Packages
We can now return to APM and generate a package with our templates and database creation scripts. Click on the atf-hello package name, and then click on the manage file information link toward the bottom of the page. Now click on scan for additional files in this package. You should see a list of the .sql, .tcl and .adp pages we installed. Indicate that all of these files should be included in the package, and after returning to the main ATF Hello APM management screen, click on the generate a new atf-hello.info file link.
You're now set to create an APM that can be distributed to any other OpenACS user. Click on the generate a file link, and the distribution file information will indicate the size of the generated APM. If you click on this link, an APM should be downloaded to your system.
How do you install a new APM someone has sent you? The easiest method is to place the APM on the server filesystem. Then from within your web browser, return to the main APM page (/acs-admin/apm/) and click on the install link. Tell the system where the APM is located, and it will be placed under the packages directory. You will then be able to install it using the APM installer that we examined last month. The data model will be inserted into the database, and the web pages will be made available for any interested parties. And of course, once a package is installed in the system, you can use the ACS site map application to mount a new instance of the package under a URL of your choice.
This example package only scratches the surface of OpenACS application development, for example:
The templating system comes with an automatic form-builder system that makes it easy to create HTML forms that automatically provide confirmation screens and data validation.
We can load Tcl procedures into AOLserver at startup time by defining them within the package's tcl directory.
Named SQL queries, as mentioned above, make it possible to write a single Tcl program that transparently accesses both Oracle and PostgreSQL.
Each instance of a package can be kept separate from its peers using the OpenACS concept of context.
Each instance can set its own parameters, allowing it to have installation-specific information.
Each package can define (or use) its own set of permissions, allowing you to create custom permissions and custom access control lists for users and groups on the system.
OpenACS is complex, and APM is not the simplest system to learn because it tries to handle so many complicated cases that web/database developers often encounter. At the same time, I haven't yet seen an easier way to distribute web/database applications with this degree of modularity, portability across databases and flexibility when it comes to the templates. The ease of creating such applications, combined with a rich data model and a large set of established applications makes OpenACS a viable and useful platform for on-line communities.
Reuven M. Lerner is a consultant specializing in web/database applications and open-source software. His book, Core Perl, was published in January 2002 by Prentice Hall. Reuven lives in Modi'in, Israel, with his wife and daughter.
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