The relational model allows designers toDatabase normalizationTo build ainformationConsistent model.Access planAnd other implementation and operation detailsDBMSThe engine should not be reflected in the logical model.This is opposite to the common practice of SQL DBMSPerformance tuningIt is often necessary to change the logical model.
The basic relationship building blocks are domains ordata type。tupleyesattributeOrder ofMultiple set(multiset). Attributes are ordered pairs of fields and values.Relational variable(relvar) is the domain and nameOrdered pairA set of (ordered pairs) that serves as a relationalHeader（header）。relationshipIs a collection of tuples.Despite theseConcept of relationshipThey are mathematically defined and can be loosely mapped to traditional database concepts.A table is a recognized visual representation of a relationship;Tuples similar tothat 's okThe concept of.
The basic principle of the relational model isInformation principle: AllinformationAre represented asData value。Therefore, the relationship variableDesign timeAre not related to each other;Instead, designers use the samefield, if an attribute depends on another attribute, theReferential integrityTo force thisdependence。
