Editing Spiral model (section)

===Use anchor point milestones===
Boehm's original description of the spiral model did not include any process milestones. In later refinements, he introduces three anchor point milestones that serve as progress indicators and points of commitment. These anchor point milestones can be characterized by key questions.
# Life Cycle Objectives. Is there a sufficient definition of a technical and management approach to satisfying everyone's win conditions? If the stakeholders agree that the answer is "Yes", then the project has cleared this LCO milestone. Otherwise, the project can be abandoned, or the stakeholders can commit to another cycle to try to get to "Yes."
# Life Cycle Architecture. Is there a sufficient definition of the preferred approach to satisfying everyone's win conditions, and are all significant risks eliminated or mitigated? If the stakeholders agree that the answer is "Yes", then the project has cleared this LCA milestone. Otherwise, the project can be abandoned, or the stakeholders can commit to another cycle to try to get to "Yes."
# Initial Operational Capability. Is there sufficient preparation of the software, site, users, operators, and maintainers to satisfy everyone's win conditions by launching the system? If the stakeholders agree that the answer is "Yes", then the project has cleared the IOC milestone and is launched. Otherwise, the project can be abandoned, or the stakeholders can commit to another cycle to try to get to "Yes."
"Hazardous spiral look-alikes" that violate this invariant include evolutionary and incremental processes that commit significant resources to implementing a solution with a poorly defined architecture.{{huh|date=August 2014}} <!-- What is meant by "architecture"? -->

The three anchor point milestones fit easily into the [[Rational Unified Process]] (RUP), with LCO marking the boundary between RUP's Inception and Elaboration phases, LCA marking the boundary between Elaboration and Construction phases, and IOC marking the boundary between Construction and Transition phases.