  Existence constraints were defined in the Relational Data Model, but,
unfortunately, are not provided by any Relational Database Management System,
except for their NOT NULL particular case. Our (Elementary) Mathematical Data
Model extended them to function products and introduced their dual
non-existence constraints. MatBase, an intelligent data and knowledge base
management system prototype based on both these data models, not only provides
existence and non-existence constraints, but also automatically generates code
for their enforcement. This paper presents and discusses the algorithms used by
MatBase to enforce these types of constraints.
