This report provides a summary of the work completed in the Source Code Assurance Tool project. This work was done as part of the Laboratory Directed Research and Development program.ii iii

The purpose of the project was to describe existing deficiencies in Geographic Information Systems for transportation (GIS-T) applications and prescribe solutions that would benefit the transportation community in general. After an in-depth literature search and much consultation with noted transportation experts, the need for a common linear reference system that integrated and supported the planning and operational needs of the transportation community became very apparent. The focus of the project was set on a unified linear reference system and how to go about its requirements definition, design, implementation, and promulgation to the transportation community. Intentionally Left Blank.. 11

We present the tool we built as part of a Laboratory Directed Research and Development (LDRD) project. This tool consists of a commercially-available, graphical editor front-end, combined with a back end "slicer."The significance of the tool is that it shows how to slice across system components. This is an advance from slicing across program components.

This report provides a preliminary functional description of a novel software application, the Source Code Assurance Tool, which would assist a system analyst in the software assessment process. An overview is given of the tool's functionality and design; and how the analyst would use it to assess a body of source code. This work was done as part of a Laboratory Directed Research and Development project.ii iii Contents

In this paper we describe a new language, Visual Structure Language (VSL), designed to describe the structure of a program and explain its pieces. This new language is built on top of a general-purpose language, such as C. The language consists of three extensions: explanations, nesting, and arcs. Explanations are comments explicitly associated with code segments. These explanations can be nested. And arcs can be inserted between explanations to show data-or control-flow.The value of VSL is that it enables a developer to better control a code. The developer can represent the structure via nested explanations, using arcs to indicate the flow of data and control. The explanations provide a "second opinion" about the code so that at any level, the developer can confirm that the code operates as it is intended to do.We believe that VSL enables a programmer to use in a computer language the same model-a hierarchy of components-that they use in their heads when they conceptualize systems.