Simply put, the numbers are the different classes that are offered by the MLIS program at the University of Western Ontario. Numbers 501 through 505 are required courese for the degree, while the rest are all electives. Here's a breakdown of the courses by number:
501 - Perspectives on Library and Information Science
502 - Organization of Information (Cataloguing)
503 - Information Sources and Services (Reference)
504 - Research Methods and Statistics
505 - Information Systems and Technology
506 - Management
520 - Digital Libraries
523 - Web Design and Architecture
558 - Database Management
598 - Services for Children and Young Adults
595 - Archives Administration
600 - Library Planning and Architecture
615 - Records Management
675 - Collections Development
716 - Archival Reference and Outreach