The Role of Natural Language in a Software Product

Formal methods as currently practiced possess a serious flaw. Formalization is the goal of a specification process, and little or no attention is paid to issues in natural language. However, natural language is necessary in any software specification because formal languages have no real-world meaning. The application domain is almost entirely informal, so some formalization process is necessary to create a symbolic representation of the part of the domain in which the program will operate. This formalization process must contain informal steps, so to facilitate the process it is imperative that all available conceptual information be gathered and organized so that it is easily accessible to the people who carry out that process. We define a new software artifact that includes not only the formal part of software, but also informal descriptions mapping formalisms to concepts in the domain. We call this new artifact a program+. The purpose of the informal part of the program+ does not end with the specification. It is theoretically possible to include only formal information after the specification stage, but in practice this is unsatisfactory. First, there is a strong chance that some error occurred in the formalization of the program. Such errors often present themselves during coding or testing, and are difficult to locate and correct. We hypothesize that much of this difficulty stems from a lack of understanding of domain issues related to such errors, and how those issues have been represented throughout the formal part of the software. We also describe a method to include necessary informal information in a software implementation. In order to build this new software artifact, a new software development process is required. This process must include not only steps for building the informal part of the iv program+, but also a procedure for gathering the domain knowledge necessary in order to build it. We call this type of process a Hamilton process, after the first person to use the word formal in this context. We demonstrated feasibility of building a program+ and refined our ideas about what it must entail by building a portion of a commercial surgical planning software tool for implanting radioactive material into tissue. We chose to rebuild the dose calculation mechanism of the current production version of the tool, which determines the amount of radiation delivered to tissue from source placement. The mechanism was specified and implemented in the style of a program+, …