Interfacing Relational Databases to the Web
The remaining design step is deciding what sort of capabilities we wish to grant users to access and update the data. This is perhaps not as much of a problem in our database, but what if we were designing a database of employees? It might cause great discord in the office if everyone knew the salary of the guy who spends every day surfing the Web and taking two-hour lunch breaks; however, they should be able to access his name, department and extension. Likewise, they shouldn't be able to change that information unless they are the department secretary or manager.
We do want some protection on our address book, so that you can type in your grandmother's e-mail address with the peace of mind that a spammer can't get it just by accessing your web server. We also don't want to bother the user with implementation details like unique ID numbers on each record—this should be a user-friendly address book. Therefore, we will allow the following:
A user can retrieve records from her own address book.
A user can insert and delete records in her own address book.
The user will be shown only what she needs to see.
To this end, we create views. A view can be just a few columns of a table or a few columns of a join. In SQL, a view is defined with the CREATE VIEW statement, which creates a view from a SELECT statement. A view can be accessed just like a table, except you can't perform inserts, updates or deletes on it. Some of the views in our example application also use PostgreSQL functions to make the final application programming easier, i.e., “make a mailto URL from this e-mail address”.
We also make note of the constraints which we cannot enforce with views: for example, the consideration that one may view only her own address book. We must implement these constraints in the application program.
Implementation in PHP3 is quite straightforward; many things in the example code speak for themselves, and others are well-commented.
The source code for the example application is intended to be more of a teaching tool than a finished product. It works well, but you would certainly want to add features before making a large-scale service from it. I have released it under the GNU GPL, so feel free to modify my code and share your modifications with others. This code is also on the FTP site shown above.
Will Benton can be reached at email@example.com
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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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