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The color code in Figure \ref{fig:stack} adds a different dimension to this diagram and taps into a different characteristic of the Iris architecture: extensibility. In particular, blue boxes with purple letters denote extensible components of the architecture, i.e. component that offer hooks into the Iris architecture to users and developers. The orange labels, on the other hand, express components that were not even part of the Iris design, but that can be loaded in Iris as plug-ins, possibly providing an interface to access non-standard services. Some of these plug-ins, along with a description of the design of the Iris Software Development Kit, will be introduced in section \ref{sec:plugins}.  The Iris development team also faced some extra challenges: our team was distributed in nature, with developers and managers working from different institutions with different tools and practices \cite{http://adsabs.harvard.edu/abs/2012SPIE.8449E..0IE}. \cite{2012SPIE.8449E..0IE}.  Moreover, willing to reuse existing software instead of reinventing the proverbial wheel, we had to integrate different existing software components in a seamless way. In summary, the Iris framework, which we will describe more in detail in the following sections, was designed to address several different requirements:  \begin{itemize}