This is a one-to-one (1:1 connectivity) ER Diagram that illustrates that one Child completes one Chore (cardinality). The lines on the Crow’s Feet indicate that the child is one of many and the chore can be zero or one. The green boxes are the entities and the orange diamond represents the relationship between the two. 1 The circle with the line at the end of the Chore entity shows that a child can theoretically complete no chore for the day, and this makes the entity ‘optional’.2
DISHES OUT 1 CHORE LIST
M CHORE CLEAN ROOM LAUNDRY LIVING ROOM
This ER Diagram indicates that one Chore List contains many Chores. The two lines at the end of the Chore List entity indicate that there is one and only one Chore List, not one Chore List of many. The relationship ‘Contains’ is represented by the orange diamond and the entity ‘Chore’ is labeled with Crow’s Feet that say that there are many chores. Attributes of the Chore entity are labeled in blue circles, showing the many ‘Chores’ that are on the ‘Chore List’. Cardinality is the relationships explained in numbers 2, so the cardinality of this diagram would be one Chore List and five Chores. The connectivity of the diagram is 1:M, which is the relationship expressed in one-to-one (1:1), one-to-many (1:M), or many-to-many (M:N)3 .
KINGDOM HEARTS SHAMSI ALI M CHILD ADHAN ANGELES OWNS M PS2 GAMES
KINGDOM HEARTS 2
This ER Diagram shows a M:N, or a many-to-many relationship. This shows that many Child(ren) own(s) many PS2 Games, as the Chen Diagram, created by Peter Chen 4 , indicates. The green boxes labeled ‘Child’ and ‘PS2 Games’ are the entities. The orange diamond labeled ‘owns’ is the relationship. The blue circles that branch off of ‘Child’ list the many children and are considered attributes. The blue circles branching off of PS2 Games indicate the many PS2 Games that are owned and are also attributes. The cardinality is four children own five PS2 Games, and the connectivity is M:N.
KINGDOM HEARTS ANGELES SHAMSI
KINGDOM HEARTS 2
ALI CHILD ADHAN
M OWNS 1
M PS2 GAMES I NINJA
DYNASTY WARRIORS CHORE LIST 1
M CONTAINS CHORE
CLEAN ROOM LAUNDRY LIVING ROOM
Above is an example of all three ER Diagrams connected.
2. http://searchcrm.techtarget.com/sDefinition/0,290660,sid11_gci333128,00.html example of a 1:M ERD. 3. http://www.utexas.edu/its/windows/database/datamodeling/dm/erintro.html 4. http://homepages.gold.ac.uk/mark/cis104/node14.html 5. http://www.infocom.cqu.edu.au/Courses/spr2000/95169/Extra_Examples/ERD.ht m Examples of a 1:1, 1:M, and M:N ERD. 6. http://kogs-www.informatik.unihamburg.de/~haarslev/publications/avitvl96/node3.html Example of a 1:1 ERD. 7. http://en.wikipedia.org/wiki/Image:ER_Diagram_MMORPG.png Example of 1:M and M:N ERD.