When building Rich Internet Applications, eventually you will have to consider file sizes and download times. The Flex Framework offers several alternatives for separating application code into separate SWF files to enrich the user experience.
Runtime shared libraries (RSLs) are files that can be downloaded and cached on a client. After an RSL is downloaded and persists on the client, multiple applications can access assets from that cached RSL. Applications can load two types of RSLs: unsigned and signed. Unsigned RSLs, such as standard and cross-domain SWF files, are stored in the browser cache. Signed RSLs, which are libraries that have been signed by Adobe and have the .swz extension, are stored within the Flash Player cache.
As the name suggests, an RSL is loaded at runtime and is considered
a dynamically linked library. Statically linked libraries are SWC files
that you compile into an application by using the
include-libraries compiler options. Application SWF files using statically linked libraries generally have a larger file size and take longer to download yet have the added benefit of running quickly because all the code is available to the application. Applications employing RSLs load faster and have a smaller file size, but may take more time at start up while loading the RSLs and increase memory usage as a consequence. The power of using RSLs becomes apparent when considering multiple applications that ...