Nov 3

Building Simple Interfaces

I’m presently over in Taiwan presenting at ICOS, and one of the things I’m looking at is one of Joomla!’s 2007 Summer of Code student’s final project. Its an email interface for publishing into Joomla!, and it raises what I find is the interesting concept: building a simple interface into a more complicated thing and allowing that simple interface to provide the basis of a more advanced system.

When I consider this more and more I look at the ability for systems to build up more advanced using simpler tools. It is actually the basis of the UNIX philosophy, lots of small tools doing their own thing really well and then tying them all together to build a more advanced product, perhaps a GUI interface or something that automates things.

When you step back and think about it, the internet is based on a similar concept. If you look at a really common protocol like HTTP or SMTP you can easily write and send valid protocol responses without too much effort by hand. And then you look at what is built on top of that, we have products like Mozilla Firefox which provide a nice GUI interface into the system and allow the user to graphically browse the web and saves them from having to see the raw HTTP that is being transmitted with each and every request.

So how does this relate to my part of the world? Well at present I’m writing a metadata file system (the sort of thing you do in your spare time…no really!) and part of its interface is utilising the file system to provide the system interface instead of writing a full API to manipulate the metadata part of the filesystem. What I’m using is a combination of the POSIX listxattr, getxattr, setxattr and other related functions. The benefit of this will mean that the system will work in locations where this is supported and will appear as a ‘natural’ part of the filesystem. This means that applications can start to take advantage of the extended attributes within the file system without having to worry about compatibility from one file system to the next (you can enable extended attributes on ext3 though they’re not structured like they are with the MDFS project). 

So starting off simple and making a flexible interface allows for the system to deploy more advanced systems at a later point without compromising on short term functionality. The development and debugging of a GUI application is harder than testing concrete scriptable interfaces such as checking that completing certain operations behaves the same way in two different circumstances, however it is easy to move from the simple interface into building the more advanced one.

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