We define a systemSystem in two ways: using a general definitionDefinition as a set of partsPart (of a system) and their relationshipsRelationship and a more specific definitionDefinition as a set of interacting agentsAgent. The latter definitionDefinition is helpful inSelf-organizing system self-organizing systemsSystem, called complex adaptive systemsComplex adaptive system. We construct a roadmapRoadmap and visionVision, usually for the next ten years. It is then easier to define the research problemsResearch problem and the actual researchResearch. The emergenceEmergence phenomenon in complex systemsComplex system makes reductionReduction and deductionDeduction impossible, and the systemsSystem are analytically intractable. There are some limitations for human knowledgeKnowledge and fundamental limitsFundamental limit of nature. We present a hierarchyHierarchy of core sciencesScience and information technologyInformation technology.