ITM 500 Lecture 6: Week 6

• School: Ryerson University
• Department: Information Technology Management
• Course: ITM 500
• Professor: Raymond Moss

Document Summary

Keys: a key consists of one or more attributes that determine other attributes. For example, an invoice number identifies all of the invoice attributes, such as the invoice data and the customer name. The attribute whose value determines another is the determinant or the key. Types of keys: a composite key is a ke(cid:455) that"s (cid:272)o(cid:373)posed of (cid:373)ore tha(cid:374) o(cid:374)e attri(cid:271)ute. An attribute that is a part of a key is called a key attribute: a superkey is a key that can uniquely identify any row in the table. All invoice are uniquely identified by their invoice number. Every non-null foreign key value must reference an existing primary key value: purpose it"s possi(cid:271)le for a(cid:374) attri(cid:271)ute not to ha(cid:448)e a (cid:272)orrespo(cid:374)di(cid:374)g (cid:448)alue, (cid:271)ut it"ll (cid:271)e impossible to have an invalid entry. The 1:1 relationship: a professor can chair only one department, and one department can have only one department chair.