Engineers who design systems using text specification documents focus their work upon the completed system to meet performance, time, and budget goals. Consistency and integrity are difficult to maintain within text documents for a single complex system, and they are more difficult to maintain as several systems are combined into higher-level systems, especially when these systems are maintained over decades, and evolve technically and in performance through updates. This system design approach frequently results in major changes during the system integration and test phase, and in time and budget overruns.