8. Identifying Objects and their Classes

• Tangible object: corresponds to a thing existing in physical sense, such as
  a keyboard, a valve, a sensor, etc...

• Role: an abstraction of an assignment or purpose of
  a person, organization, or physical object.
  For example, instructor, student, input file, auditing agency, etc...

• Incident: an abstraction of an event, occurrence, such as
  a meeting, an interrupt, an error, etc...

• Interaction: an object resulting from associations between objects.
  For example, a course registration, a club membership, etc...

• Specification: represents a rule, a standard, or criteria.
  For example, a recipe, graduation requirements, etc...