A common data model (CDM) that is a data model common to multiple application-specific data models. The CDM supports both PIM (Personal Information Manager end-user application data and line-of-business (LOB) data. Similarly, an SDM-type (system definition model) application can specify its model on top of the CDM. The CDM enables improved interoperability between applications by employing an entity component that provides a data entity having a uniform identity across a plurality of disparate applications and a relationship component that defines a relationship between two or more of the data entities. The CDM provides a type system over which any algebra will operate.