We have only scratched the surface of the OpenACS templating system. ad_page_contract additionally supports verification routines that allow you to check multiple parameters or to signal errors based on information found in the database. You actually can define your own custom error messages that may appear in the case of trouble. Even outside of ad_page_contract, a .tcl page also can call the universal ad_return_complaint function, which produces error messages in nicely formatted HTML pages.
In addition, the OpenACS templating system has a complete set of form-building routines that allow a programmer to specify an HTML form using Tcl procedures. The contents of the form then can be exported to the .adp page using data sources. Not only does the form builder cut down on the amount of HTML you have to write, but it makes it easy to create a two-stage form submission process, in which users get a chance to preview their work before sending it in.
Finally, OpenACS templates include a number of additional tags, such as <if>, that allow you to include text and images conditionally, depending on the values of other data sources.
While OpenACS is often touted as a remarkable system because of its elaborate data model and advanced applications, I have found the templates to be one of the more compelling parts of OpenACS. The graphic designers with whom I work enjoy the separation between .tcl and .adp pages, and I like that I can check for errors and pass multiple values without having to remember that there is no obvious connection between them at the HTTP level.
While the learning curve for OpenACS can be quite steep, learning how the templates work is both a gratifying and interesting way to start with this system. Given the many application packages that come with OpenACS, there also are numerous examples of the templates right in the code after you download the system.
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.
Fast/Flexible Linux OS Recovery
On Demand Now
In this live one-hour webinar, learn how to enhance your existing backup strategies for complete disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible full-system recovery solution for UNIX and Linux systems.
Join Linux Journal's Shawn Powers and David Huffman, President/CEO, Storix, Inc.
Free to Linux Journal readers.Register Now!
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- Profiles and RC Files
- Astronomy for KDE
- Maru OS Brings Debian to Your Phone
- Understanding Ceph and Its Place in the Market
- Snappy Moves to New Platforms
- Git 2.9 Released
- OpenSwitch Finds a New Home
- What's Our Next Fight?
- The Giant Zero, Part 0.x
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide