# Introduction The ER model models a database in the form of its entities and the relationships between those entities. An **entity** is an object that exists and is distinguishable from other objects. Entities have **attributes**. The **domain** of the attribute specifies the set of values that the attribute can hold. Attributes can be: * simple or composite * single-valued or multivalued attributes * derived (can be computed from other attributes) An **entity set** is a set of entities of the same type that share the same properties. A **relationship** is an association among several entities. A **relationship set** is a mathematical relation among n ≥ 2 entities, each taken from entity sets. Relationships can be **binary** (between 2 entities) or **ternary** (between 3 entities). --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://vikram-bajaj.gitbook.io/cs-gy-6083-principles-of-database-systems/main-1/the-entity-relationship-model-details/introduction.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.