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28 Cards in this Set
- Front
- Back
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optional participation
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one entity occurrence does not require corresponding entity occurrence in particular
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mandatory participation
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one entity occurrence does require corresponding entity occurrence in particular
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unary relationship
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association is maintained within single entity
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binary relationship
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association is maintained within two entities
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ternary relationship
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association is maintained within three entities
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recursive relationships
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relationship can exist between occurrences of the same entity set, naturally found in unary relationships
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associative entity
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also known as bridge entity or composite entity
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cardinality
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Assigns a specific value to connectivity. Expresses the range (minimum to maximum) of allowed entity occurrences associated with a single occurrence of the related entity.
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composite attribute
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An attribute that can be further subdivided to yield additional attributes. For example, a phone number maybe be divided into an area code, an exchange number, and a four digit code. Compare to simple attribute.
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composite identifier
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In ER modeling, a key composed of more than one attribute.
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Connectivity
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Describes the classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.
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derived attribute
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An attribute that does not physically exist within the entity and is derived via an algorithm. Example
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exsitence-dependent
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A property of an entity whose existence depends on one or more other entities. In an existence-dependent enviroment, the existence-independent table must be created and loaded first because that existence-dependent key cannot reference a table that does not yet exist.
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Existence-independent
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An entity that can exist apart from one or more related entities. It must be created first when referencing an existence-dependent table to it.
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Identifiers
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The ERM uses identifiers to uniquely identify each entity instance. In the relational model, such identifiers are mapped to primary keys in tables.
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indentifying relationship
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A relationship that exists when the related entities are existence-dependent. Also called a strong relationship or strong identifying relationship because the dependent entity’s primary key contains the primary key of the parent entity.
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iterative process
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a process based on repetition of steps and procedures.
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multivalued attribute
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An 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.
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non-identifying relationship
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A relationship that occurs when the primary key of the dependent (many side) entity does not contain the primary key of the related parent entity. Also known as a weak relationship.
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optional attribute
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In ER modeling, refers to an attribute that does not require a value, therefore it can be left empty.
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Participants
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An ER term used to label the entities that participate in a relationship. Ex
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relationship degree
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Indicates the number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher level.
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required attribute
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In ER modeling, refers to an attribute that must have a value. It cannot be left empty.
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simple attribute
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An attribute that cannot be subdivided into meaningful components. Compare to composite attribute.
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single valued attribute
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An attribute that can have only one value.
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strong relationship
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When two entities are existence-dependent
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weak entity
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An entity that displays existence dependence and inherits the primary key of its parent entity. Ex: A DEPENDENT requires the existence of an EMPLOYEE.
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weak relationship
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A relationship that exists when the PK of the related entity does not contain a PK component of the parent entity. Also known as a non-identifying relationship.
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