Thoughts and Ramblings

About 3 weeks ago, Kevin (developer of NitoTV) and I decided it was a bit silly how we were each writing playback mechanisms on the AppleTV with little to no collaboration between us. So, we decided to write a Common Media Player Framework, which is licensed using LGPL.

Kevin sent me the code he used for DVD playback inside NitoTV as a place to start. I stripped it down to a smaller piece, and started the framework. After I had it doing basic playback, I worked on overlays to provide feedback to the user. Now, hitting up and down changes the overlays between normal, chapter view, audio/subtitle selection, and zoom.

I use MacPorts to get a whole host of utilities. In addition, I’ve always used it to obtain later versions of subversion that the one provided with the OS. Xcode, on the other hand, is locked into using the version of Subversion which is installed in /usr (currently version 1.4.4 where as I have 1.6.3). Since I often work in the command line, eventually I will use the newer version of Subversion on a directory which I also use in Xcode. This causes a problem since the command line utility will upgrade the local repository format in such a way that old versions of Subversion (Xcode’s) cannot use it.

When I redesigned Sapphire, I decided that the metadata back end would be best served by Apple’s Core Data Framework. While the framework has a lot of power, several shortcomings in the implementation hindered its potential.

First, I should start with the many things that Apple did correctly in Core Data.

• The whole data model with relationships and properties is quite powerful. With this data model, one can represent many data sets in a simple manner, such as the example below:

  

  This example shows part of the data model within Sapphire pertaining to TV shows, where a TV shows contains multiple seasons, each of which contains multiple episodes. Additionally, an episode contains one or more sub-episodes, to handle the case where a single file or DVD contains multiple episodes. Lastly, the show and season objects extend from a superclass CategoryDirectory, which contains some common properties to all collections.
• Since the relationships are defined, they can be automatically maintained. In the above example, if an episode’s show relationship is set to a particular TVShow object, that show’s object will automatically have the episode added to its episodes relationship.
• Delete rules can be set such that if an object is removed, the delete can cascade to remove other objects as well. This is useful in the case of removing a directory, and all the files and directories contained within it.
• Saving to a file is easy since the details of reading and writing a file are handled by Core Data
• While I didn’t use it, undo management is also built into the system.

So, with all these advantages, why is Core Data not used more often. The answer is that it contains numerous short comings.