Methodology for Selection and Development of TransXML Schemas

Abstract

NCHRP Project 20-64, TransXML, solicited the development of standard, public domain extensible markup language (XML) schemas for the exchange of transportation data as well as the creation of a framework for the development, validation, dissemination, and extension of current and future schemas. The methodology used for the selection and development of the initial set of TransXML schemas ensured their consistency, cohesiveness, and usefulness. Data flow diagrams of the design and construction process had previously been developed for the Minnesota Department of Transportation. They articulate steps in the design process as well as the flow of data between these steps. The diagrams were analyzed to discover candidate data flows that if supported by standardized XML schemas, could improve the design and construction process. The content and structure of the data identified were then modeled with unified modeling language (UML) class diagrams–roughly one UML package per data flow. Consensus of interested parties was achieved through the project website, including specific agreement on data elements and their associations. For each element, relevant attributes were decided, along with their cardinality and data type. For associations, relationship types, cardinalities, and roles were established. Diagrams for each area were compared to achieve consistency and to identify common elements, the latter being extracted into separate UML packages. XML schemas were then developed, based on the UML packages. The geography markup language (GML) was used as the framework for the schemas, building on predefined GML elements and following GML rules for developing application schemas. Sample applications were developed to demonstrate how the schemas support the data flows.