Others regard those products which share common capabilities or provide similar services as a product family. Still others will group software products according to the technology embodied in them. For example, process control systems are based on common mathematical feedback model. In all of these overlapping notions there is the concept of a shared core. This shared core is what we define as a domain.
Domains are areas of core product expertise for which economies of scope can be realized.
Economies of scope occur when building a reusable resource and then using it in multiple products yields more income than recreating the resource in each product. The economy stems from leveraging expertise and reducing learning - major cost drivers in product development. It is dependent on a strategy that pursues market share and product differentiation. Domains are centered around a body of knowledge. Domains may be defined by a common design shared by a group of products.