MIS 325 Lecture Notes - Lecture 7: Area Codes 615 And 629, Unique Key, Bachelor Of Business Administration

• School: UT-Austin
• Department: Management Information Systems
• Course: MIS 325
• Professor: John Mote

Document Summary

Entity relationship models binary relationship - an er term for an association between two entities. For example, a phone number such as 615-898-2368 may be divided into an area code 615, an exchange number 898, and a four-digit code 2368. Compare to simple attribute. composite identifier - in er modeling, a key composed of more than one attribute. connectivity - the classification of the relationship between entities. Classifications include 1:1, 1:m, and m:n. derived attribute - an attribute that does not physically exist within the entity and is derived via an algorithm. For example, the age attribute might be derived by subtracting the birth date from the current date. existence-dependent - a property of an entity whose existence depends on one or more other entities. Such a table must be created first when referencing an existence-dependent table. identifiers - in an erm, unique names of each entity instance.