The document discusses some key concepts of the entity-relationship model for database systems. It describes how a database can be modeled as a collection of entities and relationships between entities. An entity represents a real-world object that can be distinguished from other objects, and an entity set is a collection of similar entities that share the same attributes. Entities are represented by attributes, which are descriptive properties like name, address. Attribute types can be simple, composite, single-valued, or multi-valued. An example entity set of customers is shown related to a loan entity set by a shared attribute.

1. ©Silberschatz, Korth and Sudarshan2.1Database System Concepts
Entity-Relationship Model
INDEX
 Entity Sets
Prepared by HENRY ECHEVERRÍA

2. ©Silberschatz, Korth and Sudarshan2.2Database System Concepts
Entity Sets
 A database can be modeled as:
 a collection of entities,
 relationship among entities.
 An entity is an object that exists and is distinguishable from other
objects.
 Example: specific person, company, event, plant

3. ©Silberschatz, Korth and Sudarshan2.3Database System Concepts
Entity Sets
 An entity set is a set of entities of the same type that share the
same properties.
 Example: set of all persons, companies, trees, holidays

4. ©Silberschatz, Korth and Sudarshan2.4Database System Concepts
Attributes
 An entity is represented by a set of attributes, that is descriptive
properties possessed by all members of an entity set.
 Domain – the set of permitted values for each attribute
 Attribute types:
 Simple and composite attributes.
 Single-valued and multi-valued attributes
 Derived attributes
Example: loan = (loan-number, amount)

5. ©Silberschatz, Korth and Sudarshan2.5Database System Concepts
Entity Sets customer and loan
customer-id customer- customer- customer- loan- amount
name street city number

6. ©Silberschatz, Korth and Sudarshan2.6Database System Concepts
Attributes