Learn to Create Data Model in DBMS E-R model

The Entity Relationship Model in DBMS
- The Entity-Relationship model is a set of concepts and graphical symbols that can be used to create conceptual schemas
Versions/ Evolution of the E-R Model
- Original E-R model by Peter Chen (1976)
- Extended E-R model (1986): added subtypes, now the most widely used E-R model
- Information Engineering/IE model (also called the Crow’s Foot model) developed by James Martin in 1990
- IDEF1X (1994) : national standard by the National Institute of Standards and Technology
- Additionally:
Unified Modeling Language (UML) Style E-R Models
Semantic Object Data Models (SOMs)
The Four Major Components of the E-R Model
• Entities (really entity sets)
• Attributes
• Relationships
• Identifiers
The Geometric Symbols in an E-R Model
- Entities are represented by rectangles.- Attributes are represented by ovals, that are connected to the entity by a straight line.
- Relationships are represented by diamond shaped

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.
• Eg. specific person, company, event, plant
- Entities have attributes
• Eg. people have names and addresses
- An entity set is a set of entities of the same type that share the same properties.
• Eg. set of all persons, companies, trees, holidays
Note: There are usually many instances of an entity

Entity Sets customer and loan












Attributes

- An entity is represented by a set of attributes, that is descriptive properties possessed by all members of an entity set.
- Description of the entity’s characteristics







- Domain – the set of permitted values for each attribute
- Attribute types:
• Simple and composite attributes.
• Single-valued and multi-valued attributes
E.g. multivalued attribute: phone-numbers
• Derived attributes Can be computed from other attributes
E.g. age, given date of birth

Composite Attributes