An environment for understanding of legacy real-time software

This dissertation describes an environment for understanding of large and complex legacy real-time software. Software understanding research combines analysis of legacy software and graphics-based man-machine interaction. The environment processes legacy software automatically first to create a repository, next to facilitate its understanding, and finally to create reusable components to facilitate modernizing software for the same or new application. The environment consists of the following components. (1) Legacy code representation: The legacy software is represented by a graphical language, called the Elementary Statement Language for Ada (ESL-Ada). The ESL-Ada statements and relations between the statements are represented as nodes and edges respectively. It is used as a basis for the understanding. (2) Concurrency representation: Concurrency in the legacy software, expressed in Operating System calls, are represented by Ada. The translation is accomplished by replacing the call with equivalent Ada code based on a message-based kernel oriented architecture. (3) Architecture discovery: The ESL-Ada, is partitioned into modules, called Software Units (SWUs). The SWUs are organized hierarchically based on parent-child relations. (4) State machine: The body of SWUs are represented by state machines, called Ada Real-time State Machine (ARSM). ARSM consists of states and transitions. ARSM preserves all real-time features of Ada. Each ARSM of a process (task) is a concurrently executable entity. ARSMs are hierarchically organized. (5) Simulation: The bodies of SWUs, represented by ARSMs, are simulated with test input. The outputs are obtained from the simulation. The output can be used to verify the correct execution behavior of SWUs. The graphical user interface to these components is supported by a meta graphic system, called DECDesign. This environment is the first comprehensive environment for analysis and understanding of large-scale legacy real-time software