Relationship and attribute cardinality depends on business rules. Ex: Usually Employee-WorksIn-Department maxima are one-many. If a company assigns employees to multiple departments, however, the maxima are many-many. Show
During the analysis phase, the designer looks for cardinality business rules in interviews and document review. The designer then converts business rules into 0, 1, and M specifications, and documents specifications in the entity-relationship ER diagram and glossary. Depending on the desired level of detail, cardinality does not always appear on ER diagrams. Usually, ER diagrams are drawn with software tools, which can automatically show or hide cardinality. ER diagram conventions for independent, dependent, subtype, and supertype entities vary. Many software tools allow users to choose from different conventions. After entities, relationships, attributes, and cardinality are determined, the database designer looks for dependent and subtype entities. Similar entities and optional attributes suggest new subtype and supertype entities and warrant special attention. Like other analysis steps, activities within these steps are executed iteratively. Following these steps, the database designer implements the completed entity-relationship model in SQL for a specific database. The 'implement relationships' and 'implement attributes' steps add foreign keys to the initial table design. Many-many relationships and plural attributes become new dependent tables. Unique and required cardinality is enforced with UNIQUE, NOT NULL, and PRIMARY KEY keywords. Partition rules are usually enforced in application software. After the 'implement relationships' and 'implement attributes' steps, the database is completely specified in SQL as CREATE statements. The final step, 'review tables for third normal form', ensures that tables do not contain redundant data and fine-tunes the design if necessary. What is the greatest number of instances of one entity that can relate to a single instance of another entity a maximum b minimum C one D many many?The maximum cardinality is the maximum number of entity instances that can participate in a relationship instance. There are three types of maximum cardinality: one-to-one (1:1), one-to-many (1:N) and many-to-many (N:M).
Which one refers to the number of instances in a relation?Cardinality of Relationships
Refers to the number of instances of entity A that can be associated with each instance of entity B. One-to-one: Each entity in the relationship will have exactly one related entity.
What refers to the number of entities that participate in a relationship?Cardinality: The number of times an entity of an entity set participates in a relationship set is known as cardinality.
Is an entity whose instances store attributes that are common to one or more entity subtypes?52. An entity supertype is an entity whose instances inherit some common attributes from an entity subtype and then add other attributes that are unique to an instance of the supertype.
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What is the greatest number of instances of one entity that can relate to a single instance of another entity quizlet?
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