Aspects of the subject matter described herein relate to type and property definition support for software. In aspects, new types can be added to an application model after the software has been created without changing the software. After software is created and embodied in computer code, a new type definition may be received by a user type service. The user type service may then place the new type definition in a data store in which other types native to the software are located. The software may then use the new type definitions and properties associated therewith in queries and in user interfaces provided by the software.