2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/145385Revisiting the old problem of existence of interacting models of QFT with new conceptual ideas and mathematical tools, one arrives at a novel view about the nature of QFT. The recent success of algebraic methods in establishing the existence of factorizing models suggests new directions for a more intrinsic constructive approach beyond Lagrangian quantization. Holographic projection as a simplifying tool for certain aspects of QFT turn out to be an indispensible part of these new attempts.24 pages, refereces and footnotes added, last two sections expanded Dedicated to Klaus Fredenhagen on the occasion of his 60th birthday. To appear in: "Quantum field theory --Competitive Methods", Birkhhaeuser Basel, 2008, Eds. B. Fauser, J. Tolksdorf and E. Zeidler 23 pagesHigh Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext