xz is a lossless data compression program and file format which incorporates the LZMA/LZMA2 compression algorithms. One can think of xz as a stripped-down version of the 7-Zip program. xz has its own file format rather than the .7z format used by 7-Zip (which lacks support for Unix-like file system metadata).
In general, an ePortfolio is a purposeful collection of information and digital artifacts that demonstrates development or evidences learning outcomes, skills or competencies.
The error System program problem detected comes up when a certain application crashes. Ubuntu has a program called Apport that is responsible for detecting such crashes and upon user consent, report these crashes to developers. This process intends to get the problem fixed by the developers.