Chapter 4: Entity Relationship (ER) Modeling

What is simple attribute?

Simple attribute is an attribute that cannot be subdivided into meaningful components. Compare to composite attribute.

What is single-valued attribute?

Single-valued attribute is an attribute that can have only one value.

What is binary relationship?

Binary relationahip is an ER term for an association (relationship) between two entities. For example, PROFESSOR teaches CLASS.

What is cardinality?

Cardinality is 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.

What is composite attribute?

Composite attribute is an attribute that can be further subdivided to yield additional attributes. For exampl, a phone number such as 615-898-2368 may be divided into area code (615), an exchanged number (898), and a four-digit code (2368). Compare to cimple attribute.

What is composite identifier?

Composite identifies is, in ER modeling, a key composed of more than one attribute.

What is connectivity?

Connectivity is the classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.

What is derived attribute?

Derived attribute is an attribute that does not physically exits 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.

What is existence-dependent?

Existence-dependent is a property of an entity whose existence depends on one or more other entities. In such an enviroment, the existence-independent table must be created and loaded first because the existence-dependent key cannot reference a table that does not yet exist.

What is existence-independent?

Existence-independent is 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.

What are identifiers?

Identifiers are one or more attributes that uniquely identify each entity instance.

What is strong (identifying) relationship?

Identifying or strong relationship is 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.

What is iterative process?

Iterative process is a process based on repetition of steps and procedures.

What is mandatory participation?

Mandatory participation is a relationship in which one entity occurence must have a correspondng 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.

What is multivalued attribute?

Multivalued attribute is 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.

What is weak (non-identifying) relationship?

Non-identifying or weak relationship is a relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.

What is optional attribute?

Optional attribute is, in ER modeling, an attribute that does not require a value; therefore, it can be left empty.

What is optional participation?

Optional participation is, in ER modeling, a condition in which one enitity occurrence does not require a corresponding entity occurrence in a particular relationship.

What is required attribute?

Required attribute is, in ER modeling, an attribute that must have a value. In other words, it cannot be left empty.

What is participants?

Participants is 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.

What is recursive relationship?

Recursive relationship is 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.

What is regular entity?

Regular entity is an entity that is existence-independent, that is, it can exist apart from all of its related entities...Also called a strong entity.

What is relational schema?

Relational schema is the organization of a relational database as described by the database administrator.

What is relationship degree?

Relationship degree is the number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher.

What is strong entity?

Strong entity is an entity that is existence-independent, that is, it can exist apart from all of its related entities...Also called a regular entity.

What is ternary relationship?

Ternary relationship is an ER tern used to describe an association (relationship) between three entities. For example, a DOCTOR prescrives a DRUG for a PATIENT.

What is unary relationship?

Unary relationship is an ER term used to describe an association within an entity. For example, an EMPLOYEE might manage another EMPLOYEE.

What is weak entity?

Weak entity is an entity that displays existence dependence and inherits the primary key of its parent entity. For example, DEPENDENT requires the existence of an EMPLOYEE.