Lesson 4 Flashcards
binary relationship
An ER term for an association (relationship) between two entities. For example, PROFESSOR teaches CLASS.
cardinality
A 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 attribute
An 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 identifier
In ER modeling, a key composed of more than one attribute.
derived attribute
An 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-dependent
A 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-independent
A 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.
identifiers
One or more attributes that uniquely identify each entity instance.
iterative process
A process based on repetition of steps and procedures.
mandatory participation
A 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 attributes
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.
non-identifying relationship
A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.
optional attribute
In ER modeling, an attribute that does not require a value; therefore, it can be left empty.
optional participation
In ER modeling, a condition in which one entity occurrence does not require a corresponding entity occurrence in a particular relationship.
participants
An 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 relationship
A 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.
relational schema
The organization of a relational database as described by the database administrator.
relationship degree
The number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher.
required attribute
In ER modeling, an attribute that must have a value. In other words, it cannot be left empty.
simple attribute
An attribute that cannot be subdivided into meaningful components. Compare to composite attribute.
single-valued attribute
An attribute that can have only one value.
strong (identifying) relationship
A 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 entity
An entity that is existence-independent, that is, it can exist apart from all of its related entities. Also called a regular entity.
ternary relationship
An ER term used to describe an association (relationship) between three entities. For example, a DOCTOR prescribes a DRUG for a PATIENT.
unary relationship
An ER term used to describe an association within an entity. For example, an EMPLOYEE might manage another EMPLOYEE.
weak entity
An 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 relationship
A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.
The entity relationship model (ERM) is dependent on the database type. (T/F)
False
The Crow’s Foot notation is less implementation oriented than the Chen notation. (T/F)
False
An entity in the entity relationship model corresponds to a table in the relational environment.
True
In the entity relationship model, a table row corresponds to an entity instance. (T/F)
True
In the Chen and Crow’s Foot notations, an entity is represented with a rectangle containing the entity’s name. (T/F)
True
In the original Chen notation, each attribute is represented by an oval with the attribute name connected to an entity rectangle with a line. (T/F)
True
Software vendors have adopted the Chen representation because of its compact representation (T/F)
False
A composite identifier is a primary key composed of more than one attribute. (T/F)
True
The Crow’s Foot notation easily identifies multivalued attributes. (T/F)
False
Composite attributes make it easier to facilitate detailed queries. (T/F)
False
Relationships between entities always operate in one direction. (T/F)
False