Jan 21, Ron McFadyen1 Domain Modeling Specification classes “need-to-know” associations Reflexive associations “association checklist”

Jan 21, Ron McFadyen2 Specification (Description) conceptual classes P. 142: Include a specification class when we need a description of something irrespective of its existence deletions result in loss of information it reduces duplicated information Sale SaleLineItemProductSpecification

Jan 21, Ron McFadyen3 Specification (Description) conceptual classes Flight destination arrival vs Flight destination arrival Airport Destination and arrival airports as attributes Destination and arrival airports as associations vs

Jan 21, Ron McFadyen4 Specification (Description) conceptual classes Flight is a class that keeps track of flight number, date and time for a flight, departure and arrival airports. departs from arrives in arrival departure * *1 1 Flight number date time name address Regardless of the date/time of a flight, the number and the airports involved stay constant. Airport

Jan 21, Ron McFadyen5 Specification (Description) conceptual classes Flight date time Larman suggests the use of a Description/Specification Conceptual Class to hold these attributes - to avoid an anomaly relating to information disappearing due to objects being deleted. FlightDescription number * 1 departs from arrives in arrival departure * *1 1 name address Airport

Jan 21, Ron McFadyen6 Page 164: Focus on those associations for which knowledge of the relationship needs to be preserved for some duration “need-to-know” associations Avoid showing redundant or derivable associations “need-to-know” associations correspond to verbs expressing a relationship between classes objects do not exist in isolation - they fit together in some way

Jan 21, Ron McFadyen7 “need-to-know” associations Flight date time Our database needs to record, to keep track of, when flights are scheduled, where they fly from and to - I.e. we need to know (or be able to derive) this information. FlightDescription number * 1 departs from arrives in arrival departure * *1 1 name address Airport

Jan 21, Ron McFadyen8 “need-to-know” associations departs from arrives in arrival departure Flight date time name address We can always derive the departure and arrival airports for a flight, so we don’t need to have these 2 redundant relationships Airport FlightDescription number * 1 * * 1 1 arrival departure

Jan 21, Ron McFadyen9 * 0..1 Page 158: “ a person can be Married-to only one other person at any particular moment, even though... Person is Married to ? Reflexive associations

Jan 21, Ron McFadyen10 Page 160: ? Person Supervises Reflexive associations *

Jan 21, Ron McFadyen11 Pages 156, 162: “association checklist” typical ways in which associations arise A is physically contained in B … Section in a Book A is an organizational subunit of B … Faculty in a University etc Association checklist