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C175 Ch.4

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verickle's version from 2017-08-21 20:01

Attributes

Question Answer
Required AttributeAn attribute that must have a value.
Optional AttributeAn attribute that does not require a value; therefore, it can be left empty.
DomainThe set of possible values for a given attribute.
Identifiers (Primary Keys)One or more attributes that uniquely identify each entity instance.
Composite IdentifiersA primary key composed of more than one attribute.
Composite AttributeAn attribute that can be further subdivided to yield additional attributes.
Single-Valued AttributeAn attribute that can have only a single value.
Multivalued AttributeAttributes that can have many values.
Derived AttributeAn attribute whose value is calculated from other attributes.
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Glossary

Question Answer
binary relationshipAn ER term for an association (relationship) between two entities. For example, PROFESSOR teaches CLASS.
cardinalityA property that assigns a specific value to connectivity and expresses the range of allowed entity occurrences associated with a single occurrence of the related entity.
composite attributeAn attribute that can be further subdivided to yield additional attributes. For example, a phone number such as 615-898-2368 may be divided into an area code (615), an exchange number (898), and a four-digit code (2368). Compare to simple attribute.
composite identifierIn ER modeling, a key composed of more than one attribute.
derived attributeAn attribute that does not physically exist within the entity and is derived via an algorithm. For example, the Age attribute might be derived by subtracting the birth date from the current date.
existence-dependentA property of an entity whose existence depends on one or more other entities. In such an environment, the existence-independent table must be created and loaded first because the existence-dependent key cannot reference a table that does not yet exist.
existence-independentA property of an entity that can exist apart from one or more related entities. Such a table must be created first when referencing an existence-dependent table.
identifiersOne or more attributes that uniquely identify each entity instance.
iterative processA process based on repetition of steps and procedures.
mandatory participationA relationship in which one entity occurrence must have a corresponding occurrence in another entity. For example, an EMPLOYEE works in a DIVISION. (A person cannot be an employee without being assigned to a company's division.)
multivalued attributesAn attribute that can have many values for a single entity occurrence. For example, an EMP_DEGREE attribute might store the string "BBA, MBA, PHD" to indicate three different degrees held.
non-identifying relationshipA relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.
optional attributeIn ER modeling, an attribute that does not require a value; therefore, it can be left empty.
optional participationIn ER modeling, a condition in which one entity occurrence does not require a corresponding entity occurrence in a particular relationship.
participantsAn ER term for entities that participate in a relationship. For example, in the relationship "PROFESSOR teaches CLASS," the teaches relationship is based on the participants PROFESSOR and CLASS.
recursive relationshipA relationship found within a single entity type. For example, an EMPLOYEE is married to an EMPLOYEE or a PART is a component of another PART.
regular entitySee strong entity.
relational schemaThe organization of a relational database as described by the database administrator.
relationship degreeThe number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher.
required attributeIn ER modeling, an attribute that must have a value. In other words, it cannot be left empty.
simple attributeAn attribute that cannot be subdivided into meaningful components. Compare to composite attribute.
single-valued attributeAn attribute that can have only one value.
strong (identifying) relationshipA relationship that occurs when two entities are existence-dependent; from a database design perspective, this relationship exists whenever the primary key of the related entity contains the primary key of the parent entity.
strong entityAn entity that is existence-independent, that is, it can exist apart from all of its related entities. Also called a regular entity.
ternary relationshipAn ER term used to describe an association (relationship) between three entities. For example, a DOCTOR prescribes a DRUG for a PATIENT.
unary relationshipAn ER term used to describe an association within an entity. For example, an EMPLOYEE might manage another EMPLOYEE.
weak entityAn entity that displays existence dependence and inherits the primary key of its parent entity. For example, a DEPENDENT requires the existence of an EMPLOYEE.
weak relationshipA relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.
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