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\section{Introduction}   The Virtual Observatory (VO) provides a set of standards and protocols that enable interoperability among astronomy-centered services and applications \color{{red} [REFs]}. {\color{{red} [REFs]}}.  Building VO-enabled, interoperable applications poses several challenges to software developers. In order to design effective applications, one wants to leverage VO standards and protocols without exposing the complexity and technicality of their specifications to the users. Also, while application developers implement many desired functionalities, they must keep the door open for plugging in user's code, and allow third party developers to extend the application's functionality without being aware of the standards themselves. Designing such general purpose applications thus becomes an exercise in designing a framework that implements some basic, effective functionality for a wide set of use cases, while being highly extensible. Iris, the Virtual Astronomical Observatory spectral energy distribution (SED) analysis tool [REFs], is such a VO-enabled application. Iris was developed to provide the science community a desktop application for building, viewing and analyzing broadband spectro-photometric SEDs, while implementing VO standards and protocols and taking advantage of existing astronomy software.