This invention provides a device and method for processing data with a data processing string having push type and pull type tasks. Push tasks processes data and pushes the output of the process to downstream push tasks based on link paths. On the other hand, pull tasks sends data requests via upstream links to upstream pull tasks to acquire data for processing. Data processing strings are usually configured with either push tasks and/or pull tasks to maintain consistency in the direction of links. The preferred embodiments of this invention provides a method and apparatus for inserting push tasks in a string of pull tasks and inserting pull tasks in a string of push tasks. The inserted push and pull tasks are enhanced with forward and backward message links and interface tasks are provided to interface between the inserted pull or push tasks in the strings of push or pull tasks, respectively.