Commonality and variability play central roles in all product line development processes. Indeed, at each phase of core assets development, variabilities can exist at different levels of abstraction and in addition can be concretized by different artifacts. In this paper, we suggest a 2-dimensional framework for analyzing variabilities of core assets in software product lines. In the vertical analysis, variations are analyzed at different abstract levels, in which the region of commonality is first identified, and variation points are accordingly defined. In the horizontal analysis, variation types are elaborated according to the characteristics of requirements and architecture. With this framework, the variability of assets can be consistently and explicitly described, allowing variations to be traced in core assets and seamless reuse of core assets across the entire life cycle.