Definition: Attributes are properties used to represent entities. In a data model, entities are like the nouns, and attributes are like the adjectives describing those nouns.
Values: All attributes have values. For example, a student entity may have attributes like name, class, and age, each with specific values.
Domain: There is a domain or range of values that can be assigned to attributes. This sets constraints on what kind of values an attribute can have. For instance, a student’s name must be alphabetic, and age cannot be negative.
Domain:
Definition: A domain is an attribute constraint that determines the type of data values allowed for that attribute. It defines the acceptable range or set of values for an attribute.
Size: Attribute domains can vary in size, meaning they can be broad or narrow depending on the requirements.
Types of Attributes in a Conceptual Data Model:
Simple Attribute:
Description: Atomic values that cannot be further divided.
Example: Student’s phone number with 10 digits.
Composite Attribute:
Description: Made up of more than one simple attribute.
Example: Student’s complete name composed of first_name and last_name.
Derived Attribute:
Description: Values are not physically stored but derived from other attributes.
Example: Calculating average_salary in a department based on individual salaries.
Single-Value Attribute:
Description: Contains a single value.
Example: Social Security Number for an individual.
Multi-Value Attribute:
Description: Can contain more than one value.
Example: A person can have multiple phone numbers or email addresses.
