Because software is defined as a hierarchy of models instead of code only, the task of software development is to build this model hierarchy. The methodology to build this model hierarchy is called Unified Content. With UC, software development is a model-building activity along the model hierarchy. The bottom level of the hierarchy, the business model, contains all the required modeling components to be implemented at the levels above. The development process is to build the business model first and then refine and branch out these components, bottom up, level by level. UC is business-driven, irreversible growth, and model orientation. UC workflow contains activities of building four models: business, technology, design model, and cod. (See Figure below)