Engineering diagnosis often involves analyzing complex records of system states printed to large, textual log files. Typically the logs are designed to accommodate the widest debugging needs without rigorous plans on formatting. As a result, critical quantities and flags are mixed with less important messages in a loose structure. Once the system is sealed, the log format is not changeable, causing great difficulties to the technicians who need to understand the event correlations. We describe a modular system for analyzing such logs where document analysis, report generation, and data exploration tools are factored into generic, reusable components and domain-dependent, isolated plug-ins. The system supports incremental, focused analysis of complicated symptoms with minimal programming effort and software installation. We discuss important concerns in the analysis of logs that sets it apart from understanding natural language text or rigorously structured computer programs. We highlig...