The earliest example of equine footwear we have is made of animal hide and dates from about 600 B.C. This primitive hoof protector looks more like a horse bootie than what we think of today as a horseshoe. It was probably stuffed with dried grass or other available natural material and tied on with hide thongs.
The spiral model is a software development process combining elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. The spiral model was defined by Barry Boehm in his article A Spiral Model of Software Development and Enhancement from 1985. This model was not the first model to discuss iterative development, but it was the first model to explain why the iteration matters.
Each increment of capability will have its own set of threshold and objective values set by the user. Spiral development is an instance of an incremental development strategy where the end state is unknown. Technology is developed to a desired maturity and injected into the delivery of an increment of capability. (Source: CJCSI 3170.01I â Joint Capabilities Integration and Development System)