A method for designing a system LSI includes the step of defining, for
each of instructions of the processor, a behavior function description
and an instruction description specifying the behavior function
description, and the step of synthesizing the instructions by behavior
synthesis to define the processor. The behavior function description and
the instruction description are separately stored in a database as design
resources for the next design of a system LSI. The instruction
description is retrieved as accompanied by the associated behavior
function description from the database.