Part2-ERM - ENTITY-RELATIONSHIP MODEL HIGH-LEVEL,...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
ENTITY - RELATIONSHIP MODEL HIGH-LEVEL, CONCEPTUAL DESCRIPTION OF: ENTITIES (OBJECTS) THEIR ATTRIBUTES (COMPONENTS) THEIR RELATIONSHIPS (CONNECTIONS) ENTITIES ARE OBJECTS (PHYSICAL OR CONCEPTUAL THINGS WHICH HAVE AN INDEPENDENT EXISTENCE) PERSON, PROJECT, COURSE, … ENTITIES HAVE ATTRIBUTES PERSON(NAME, AGE, ADDRESS) ATTRIBUTES HAVE DOMAINS (ALLOWABLE VALUES) (BUT NO VALUES IN ERM - THERE ARE NO SPECIFIC INSTANCES) WHAT MAKES A VIABLE ENTITY? UNIQUE IDENTIFIER. MULTIPLE ATTRIBUTES. MULTIPLE INSTANCES. NOT REDUNDANT. RELATIONSHIPS TO OTHER ENTITIES.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
RELATIONSHIPS EXIST BETWEEN ENTITIES THE DEGREE OF A RELATIONSHIP IS NUMBER OF PARTICIPATING ENTITY TYPES. EMPLOYEE SSN DEPARTMENT NAME WORKS NAME ADDRESS IN PHONE SALARY LOCATION BINARY RELATIONSHIPS COWBOY RIDES BULL ENTERS RODEO USED TERNARY RELATIONSHIP COWBOY RIDES BULL RODEO THREE BINARY RELATIONSHIPS ARE NOT THE SAME AS A TERNARY RELATIONSHIP. IN GENERAL, THE HIGHER THE DEGREE OF A RELATIONSHIP, THE MORE RESTRICTIVE IT IS.
Background image of page 2
NAME IDENTIFIES THE ROLE OF AN ENTITY IN A RELATIONSHIP STUDENTS ENROLL CLASS STUDENT IN CLASS THIS IS NORMALLY SELF-EVIDENT, BUT NOT ALWAYS. RELATIONSHIPS CAN HAVE ATTRIBUTES TOO STUDENTS ENROLL CLASS IN STUDY HOURS RELATIONSHIP ATTRIBUTES ARE DEPENDENT ON ALL ENTITIES PARTICIPATING IN THE RELATIONSHIP . STRUCTURAL CONSTRAINTS PARTICIPATION TOTAL - EVERY DEPARTMENT MUST HAVE AT LEAST ONE EMPLOYEE. PARTIAL
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/12/2010 for the course CMPS 460 taught by Professor Jim during the Spring '10 term at École Normale Supérieure.

Page1 / 12

Part2-ERM - ENTITY-RELATIONSHIP MODEL HIGH-LEVEL,...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online