The lack of one holistic view on technology mediated learning and teaching (LT) complicates and hinders development of adaptive LT oriented Learning Technology Systems (LTS) and integration of independently developed educational components intended for specific educational tasks. We introduce the Systemic-Structural Theory of Activity (SSTA) that gives way to resolve the psychological and pedagogical issues in formally modelling LTS under the umbrella of one holistic LT activity. This paper demonstrates relevancy of SSTA, discusses conceptual, strategic, semantic, heuristic, algorithmic, logical, computational, and self-regulative viewpoints, and addresses relevant software engineering research issues for adaptive LTS design.