1. A computer system, comprising: task model holding means for holding a task model, which is a collection of knowledge, modeled after task execution pattern of a user; context information holding means for holding context information, which is a knowledge to represent a context of task execution of the user, sequentially calculated and updated based on input information from task model and operation series of the user; task execution means for making access to software functions necessary to task execution wanted by the user referring to the task model and the context information based on input operation by the user and for converting the results of execution of the software functions to adequate expression to present to the user, referring to the task model and context information; whereby there are further provided: task description holding means for holding a collection of task descriptions formally describing individual utilization patterns of the software functions; and filtering means for finding and selecting a task description describing utilization pattern, not tried by the user in the past and regarded as useful to the user, from a collection of task descriptions held by the task description holding means, and for disclosing it to the user.