1. A computer-implemented method of automatically deploying an information technology (IT) system instance having hardware and software components, said method comprising: receiving, by a computer system, functional requirements of said IT system instance; receiving, by said computer system, non-functional requirements of said IT system instance; subsequent to said receiving said functional requirements, generating, by said computer system, use cases describing said functional requirements of said IT system instance; subsequent to said generating said use cases and based on components consisting of said use cases, system context diagrams, component models, operational models, and data flow diagrams, generating, by said computer system, an application model of said software components, wherein said generating said application model includes representing said software components in a software component modeling language; based on said application model and said generated use cases, generating, by said computer system, an infrastructure model of infrastructure components consisting of an operating system, middleware, and a specification of a physical environment required to host said software components, wherein said generating said infrastructure model includes representing said hardware components in said software component modeling language; based on said application model and said infrastructure model, generating, by said computer system, a computer file in a markup language, wherein said computer file includes a design of said IT system instance having said hardware and software components, and further includes first instructions for accessing first assets stored in an infrastructure runtime source library and second instructions for accessing second assets stored in a software source library, and wherein said first assets specify said hardware components and said second assets specify said software components; and exporting, by said computer system, said computer file in said markup language to a deployment tool, wherein a result of said exporting said computer file to said deployment tool is an automatic deployment of said IT system instance based on carrying out said first and second instructions included in said computer file to access said first and second assets stored in said infrastructure runtime source library and said software source library, respectively, wherein said generating said application model, said generating said infrastructure model based on said application model, said generating said computer file in said markup language, said exporting said computer file to said deployment tool, and said automatic deployment of said IT system instance resulting from said exporting said computer file to said deployment tool are steps performed automatically in succession without a human-performed step being performed between any of said steps, wherein said computer system includes software-based generators that consist of first, second, third and fourth software-based generators which perform said steps, wherein said first generator is a use case generator that performs said generating said use cases, wherein said second generator is an application model generator that performs said generating said application model of said software components, wherein said third generator is an infrastructure model generator the performs said generating said infrastructure model, and wherein said fourth generator is a deployable object generator that performs said generating said computer file in said markup language.