A method and system for creating and modifying computer applications using an application description language based on a markup language is provided. An engine creates, connects, and initializes objects corresponding to entities, and specified by entity tags. A factory may be specified by an entity tag and used to create a plurality of entities. Applications are specified in a plaintext descriptive language using a markup language such as XML, enabling applications to be easily developed using object oriented techniques and abstraction. Altering preexisting applications is also simplified. Finally, an application may be dynamically reconfigured when the application's data changes. Type checking and conditional creation of entities is supported.