Unitary entities
Names can be split into personal names and corporate names. You decide that all names should have the same features in this model; that is, you do not plan to record different information about a company than you would record about a person. Likewise, you decide that only one kind of address exists; you are not required to treat home addresses differently from business addresses.
However, you also realize that more than one kind of telephone number exists. Voice numbers are answered by a person, fax numbers connect to a fax machine, and modem numbers connect to a computer. You decide that you want to record different information about each kind of number, so these three types are different entities.
- Name
- Address (mailing)
- Telephone number (voice)
- Telephone number (fax)
- Telephone number (modem)