问题
Does the double line in the following ER diagrams means total participation or recursive relation?
Could anyone tell me the notation difference for both?
回答1:
Total Participation: Every entity in the set is involved in some association (or tuple) of the relationship.
Recursive Relationship: An entity set relating to itself.
Most commonly in recursive relationships they indicate the different types of roles an entity can have (e.g., the different ways it can participate) in a relationship by writing each role above each line.
An example of this would be in a Course table with a relational table of Prerequisites
A Course could be both the Prerequisite and the Course and you would write those on each line.
Here's another example.
Assuming your textbook follows a similar pattern, I would assume that these are in fact total participation constraints.
回答2:
double line : Used to represent total participation of an entity in a relationship set.
A recursive relationship is one in which the same entity participates more than once in the relationship.
recursive relationship example : Suppose one team is assigned the task of supervising the other teams. This supervisor team makes sure that each team records its portion of the data. The supervision relationship is a recursive relationship because the same entity, a particular team, participates more than once in the relationship, as a supervisor and as a supervisee. To draw the situation, we label the two lines between team and supervision with the two possible roles
by this definitions all three above are total participation
回答3:
defination of total participation constraints: the participation of an entoty set E in the eelationship R is said to be a total if every entity in E participates in at least one relationship in R.
来源：https://stackoverflow.com/questions/19781294/whats-the-difference-in-notation-for-total-participation-and-recursive-relation