AboutIain M Watson Expertise I have 15 years of SQL experience in several large scale business catagories. I have many programs involving complicated SQL queires in both DB2 and Orcale databases. I have many years experience dealing with Database administrators in performance/tuning and implementing large scale SQL systems.
Experience I have designed many complicated SQL queries involving many aspects of the SQL syntax to obtain information from large databases with performance and efficiency as a major consideration.
Education/Credentials Bachelors degree in Computer Science.
Question I have a question on a homework problem asking me to Identify the mandatory/optional dependencies for the relationships. I do not understand what this means. Could you please help.
Answer Hi, this look like a relational databases question ?? If so then we are talking about existence dependency. Existence dependency describes whether an entity in a relationship is optional or mandatory. when you build a database from the beginning, you need to analyze your business rules to identify whether an entity must exist in a relationship.
For example, your business rules might dictate that an address must be associated with a name. Such an association indicates a MANDATORY existence dependency for the relationship between the name and address entities. An example of an OPTIONAL existence dependency could be a business rule that says a person might or might not have children.
All relational databases have to have rules or business rules. From the initial design all the relationships have to be designed correctly otherwise later on when you use the database model, the data retrieved, manipulated or even deleted could be wrong ad give incorrect results.
There is also connectivity in relationships, you can have
- one to one (example, 1 person per account id)
- one to many ( example, 1 account id can have many address lines)
- many to many ( a patient can be covered by multiple insurance plans, and an insurance company may have multiple patients.
