The Part 21 Working Set library is an extension of the ROSE library for extracting and processing data from very large STEP files. These operations are done "out-of-memory;" the original large file is never loaded into memory as C++ objects. Operations are done on the file as a text stream, and can run quickly.
For simple operations on large files, this technique can be faster than reading the entire file into memory with the ROSE library. On files less than a few megabytes in size, or with more complex operations, the ROSE library will outperform the Part 21 Working Set library.