This document discusses entity-relationship (E-R) modeling. It defines the key components of an E-R model, including entities, attributes, keys, relationships, and structural constraints. Entities can be strong or weak. Attributes have domains and can be single-valued or multi-valued. Relationships associate entities and have degrees and constraints like cardinality. The enhanced E-R model adds entity types like subclasses and superclasses, as well as attribute and constraint inheritance. The document provides steps for designing an E-R diagram, including identifying entity types and relationships, then shows an example E-R diagram for a rental management system.