A characteristic of an entity or object. An attribute has a name and a data type.
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business rule
Narrative descriptions of a policy, procedure, or principle within an organization. Examples: A pilot cannot be on duty for more than 10 hours during a 24-hour period. A professor may teach up to four classes during any one semester.
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class
A collection of like objects with shared structure (attributes) and behavior (methods). A class encapsulates an object's data representation and a method's implementation. Classes are organized in a class hierarchy.
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class hierarchy
The organization of classes in a hierarchical tree where each "parent" class is a superclass and each "child" class is a subclass.
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conceptual model
The output of the conceptual design process. The conceptual model provides a global view of an entire database. Describes the main data objects, avoiding details.
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conceptual schema
A representation of the conceptual model, usually expressed graphically.
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connectivity
Describes the classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.
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constraint
A restriction placed on data. Constraints are normally expressed in the form of rules. Example: "A student's GPA must be between 0.00 and 4.00." Constraints are important because they help to ensure data integrity.
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data definition language (DDL)
The language that allows a database administrator to define the database structure, schema, and subschema.
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data manipulation language (DML)
The language (set of commands) that allows an end user to manipulate the data in the database (SELECT, INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK).
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data model
A representation, usually graphic, of a complex "real-world" data structure. Data models are used in the database design phase of the database life cycle.
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entity
Something about which someone wants to store data; typically a person, a place, a thing, a concept, or an event.
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entity instance
A term used in ER modeling to refer to a specific table row. Also known as an entity occurrence.
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entity relationship diagram (ERD)
A diagram that depicts an entity relationship model's entities, attributes, and relations.
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entity set
In a relational model, refers to a grouping of related entities.
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internal model
In database modeling, refers to a level of data abstraction that adapts the conceptual model to a specific DBMS model for implementation.
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internal schema
Depicts a specific representation of an internal model, using the database constructs supported by the chosen database.
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logical design
A stage in the design phase that matches the conceptual design to the requirements of the selected DBMS and is, therefore, software-dependent.
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logical independence
A condition that exists when the conceptual model can be changed without affecting the external model.
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many-to-many (M:N or *..*) relationship
One of three types of relationships (associations among two or more entities) in which one occurrence of an entity is associated with many occurrences of a related entity and one occurrence of the related entity is associated with many occurrences of the first entity.
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one-to-many (1:M or 1..*) relationship
One of three types of relationships (associations among two or more entities) that are used by data models. In a 1:M relationship, one entity instance is associated with many instances of the related entity.
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one-to-one (1:1 or 1..1) relationship
One of three types of relationships (associations among two or more entities) that are used by data models. In a 1:1 relationship, one entity instance is associated with only one instance of the related entity.
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physical independence
A condition that exists when the physical/internal model can be changed without affecting the conceptual model.
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physical model
A model in which the physical characteristics (location, path, and format) are described for the data. Both hardware- and software-dependent.
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relation
In a relational database model, an entity set. Relations are implemented as tables. Relations (tables) are related to each other through the sharing of a common entity characteristic (value in a column).
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relational database management system (RDBMS)
A collection of programs that manages a relational database. The RDBMS software translates a user's logical requests (queries) into commands that physically locate and retrieve the requested data.
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relational diagram
A graphical representation of a relational database's entities, the attributes within those entities, and the relationships among those entities.
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relational model
Developed by E. F. Codd (of IBM) in 1970, it represents a major breakthrough for users and designers because of its conceptual simplicity. The relational model, based on mathematical set theory, represents data as independent relations.
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relationship
An association between entities.
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schema
A logical grouping of database objects (tables, indexes, views, queries, etc.) that are related to each other. Usually, a schema belongs to a single user or application.
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table
A (conceptual) matrix composed of intersecting rows (entities) and columns (attributes) that represents an entity set in the relational model. Also called a relation.
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domain
In data modeling, refers to the construct used to organize and describe an attribute's set of possible values.
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entity integrity
The property of a relational table that guarantees that each entity has a unique value in a primary key and that there are no null values in the primary key.
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key, superkey, primary key, foreign key
An entity identifier based on the concept of functional dependence; may be classified as follows: Superkey: An attribute (or combination of attributes) that uniquely identifies each entity in a table. Candidate key: A minimal attribute that is itself a superkey. Primary key (PK): A candidate key selected as a unique entity identifier.
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Foreign key
An attribute (or combination of attributes) in one table whose values must match the primary key in another table or whose values must be null.
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key attribute
The attribute(s) that form(s) a primary key.
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null
In SQL, refers to the absence of an attribute value. Note: A null is not a blank.
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primary key (PK)
In the relational model, an identifier composed of one or more attributes that uniquely identifies a row.
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referential integrity
A condition by which a dependent table's foreign key must have either a null entry or a matching entry in the related table.
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relational schema
The description of the organization of a relational database as seen by the database administrator.
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binary relationship
An ER term used to describe an association (relationship) between two entities. Example: PROFESSOR teaches COURSE.
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cardinality
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
An attribute that can be further subdivided to yield additional attributes. For example, a phone number () may be divided into an area code (615), an exchange number (898), and a four-digit code (2368).
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derived attribute
An attribute that does not physically exist within the entity and is derived via an algorithm. Example: Age = current date - birth date.
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mandatory participation
A term used to describe a relationship in which one entity occurrence must have a corresponding occurrence in another entity. Example: EMPLOYEE works in DIVISION.
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multivalued attribute
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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optional participation
In ER modeling, refers to a condition where one entity occurrence does not require a corresponding entity occurrence in a particular relationship.
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participants
An ER term used to label the entities that participate in a relationship. Example: PROFESSOR teaches CLASS.
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recursive relationship
A relationship that is found within a single entity type. For example, an EMPLOYEE is married to an EMPLOYEE.
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relationship degree
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
In ER modeling, refers to an attribute that must have a value. In other words, it cannot be left empty.
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simple attribute
An attribute that cannot be subdivided into meaningful components.
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single-valued attribute
An attribute that can have only one value.
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strong relationship
When two entities are existence-dependent; from a database design perspective, this exists whenever the primary key of the related entity contains the primary key of the parent entity.
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ternary relationship
An ER term used to describe an association (relationship) between three entities. Example: A CONTRIBUTOR contributes money to a FUND from which a RECIPIENT receives money.
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unary relationship
An ER term used to describe an association within an entity. Example: A COURSE is a prerequisite to another COURSE.
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weak entity
An entity that displays existence dependence and inherits the primary key of its parent entity. Example: A DEPENDENT requires the existence of an EMPLOYEE.
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