Domain
In data modeling, the construct used to organize and describe an attribute's set of possible values.
Primary key (PK)
An identifier composed
... [Show More] of one or more attributes that uniquely identifies a row. Also, a candidate key selected as a unique entity identifier. A minimal superkey.
Key
One or more attributes that determine other attributes.
Determination
The role of a key. In the context of a database table, the statement "A determines B" indicates that knowing the value of attribute A means that the value of attribute B can be looked up.
Determinant
Any attribute in a specific row whose value directly determines other values in that row.
Dependent
An attribute whose value is determined by another attribute.
Full functional dependence
A condition in which an attribute is functionally dependent on a composite key but not on any subset of the key.
Composite key
A multiple-attribute key.
Key attributes
The attributes that form a primary key
Superkey
An attribute or attributes that uniquely identify each entity in a table.
Candidate key
A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey.
Entity integrity
The property of a relational table that guarantees each entity has a unique value in a primary key and that the key has no null values.
Null
The absence of an attribute value.
Foreign key
An attribute or attributes in one table whose values must match the primary key in another table or whose values must be null.
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.
Secondary key
A key used strictly for data retrieval purposes. For example, the combination of last name, first name, middle initial, and telephone number will probably match the appropriate table row. Also called an alternate key.
Relational algebra
A set of mathematical principles that form the basis for manipulating relational table contents; the eight main functions are SELECT, PROJECT, JOIN, INTERSECT, UNION, DIFFERENCE, PRODUCT, and DIVIDE.
Relvar
Short for relation variable, a variable that holds a relation. It is a container (variable) for holding relation data, not the relation itself.
Closure
A property of relational operators that permits the use of relational algebra operators on existing tables (relations) to produce new relations.
SELECT operator
An operator used to select a subset of rows. Also known as RESTRICT.
σ cus_code = 10010
PROJECT operator
An operator used to select a subset of columns. In other words, it yields a vertical subset of a table. This operation retrieves all rows and some attributes of a table without using a WHERE clause to limit which rows of the table are included.
π cus_fname, cus_lname
UNION operator
This set operator combines the result set of two or more SELECT statements, dropping the duplicate rows.
supplier ∪ vendor
Union-compatible
Two or more tables that have the same number of columns and the corresponding columns have compatible domains.
INTERSECT operator
This set operator combines the output of two SELECT queries and returns only the rows that appear in both.
supplier ∩ vendor
DIFFERENCE
An operator used to yield all rows from one table that are not found in another union-compatible table.
supplier – vendor
PRODUCT
An operator used to yield all possible pairs of rows from two tables.
customer × agent
JOIN
In relational algebra, a type of operator used to yield rows from two tables based on criteria. There are many types, such as natural, theta, equi, and outer.
Natural join (JOIN)
A relational operation that yields a new table composed of only the rows with common values in their common attribute(s).
customer ⨝ agent
Equijoin
A join operator that links tables based on an equality condition that compares specified columns of the tables. Is a special type of theta join
Theta join
A join operator that links tables using an inequality comparison operator (<, >, <=, >=) in the join condition.
INNER JOIN
A join operation in which only rows that meet a given criterion are selected. The join criterion can be an equality condition (natural join or equijoin) or an inequality condition (theta join). This join is the most commonly used type of join.
OUTER JOIN
This join Returns a set of records that includes rows for which no corresponding match is found in the other table. Unmatched values in the related table are left null. Three types LEFT, RIGHT and FULL
LEFT OUTER JOIN
In a pair of tables to be joined, a join that yields all rows in the left table, including those that have no matching values in the other table.
SELECT *FROM T1 ____________ T2 ON T1.C1=T2.C1
RIGHT OUTER JOIN
In a pair of tables to be joined, a join that yields all of the rows in the right table, including the ones with no matching values in the other table.
SELECT *FROM T1 ____________ T2 ON T1.C1=T2.C1
FULL OUTER JOIN
Returns rows with matching values and includes all rows from both tables (T1 and T2) with unmatched values
SELECT *FROM T1 ____________ T2 ON T1.C1=T2.C1
DIVIDE operator
An operator that answers queries about one set of data being associated with all values of data in another set of data. It uses one 2-column table as the dividend and one single-column table as the divisor.
JOIN operation
This operation integrates data from two or more tables or combines them. It can be implemented in the FROM and WHERE clauses.
Data dictionary
A DBMS component that stores metadata. It contains the data definition as well as their characteristics and relationships. It may also include data that are external to the DBMS. Also known as an information resource dictionary
System catalog
A detailed system data dictionary that describes all objects in a database.
Homonyms
The use of the same name to label different attributes. Some relational software automatically check for these and either alerts the user to their existence or automatically makes the appropriate adjustments.
Synonym
The use of different names to identify the same object, such as an entity, an attribute, or a relationship; For example, car and auto refer to the same object
The 1:M Relationship
This relationship is the relational modeling ideal. One record in a table can be associated with one or more records in another table. For example, each customer can have many sales orders.
The 1:1 Relationship
This relationship should be rare in any relational database design. One entity can be related to only one other entity, and vice versa.
The M:N Relationship
This relationship cannot be implemented as such in the relational model however, it can be implemented by creating a new entity in 1:M relationships with the original entities.
Composite entity
An entity designed to transform an M:N relationship into two 1:M relationships. The entity's primary key comprises at least the primary keys of the entities that it connects. Also known as a bridge entity or associative entity.
Linking table
In the relational model, a table that implements a composite entity in a M:M relationship
Cardinality
Denotes how many instances of one object are related to instances of another object (maximum).
Modality
Denotes an instance of a specific entity is optional or mandatory in a relationship (minimum).
Unary one-to-one
A relationship between a single occurrence of an entity type with another single occurrence of the same entity type
Unary one-to-many
A relationship between a single occurrence of an entity type with any number of occurrences (minimum one) of the same entity type.
Unary many-to-many
A relationship between any occurrence of an entity type with any number of occurrences (minimum one) of the same entity type.
Index
An ordered array of key values and row ID values (pointers). They are generally used to speed up and facilitate data retrieval.
Unique index
An index in which the index key can have only one associated pointer value (row).
Flags
Special codes implemented by designers to trigger a required response, alert end users to specified conditions, or encode values. May be used to prevent nulls by bringing attention to the absence of a value in a table.
Prime attribute
An attribute that is part of a key or is the whole key.
Set theory
A part of mathematical science that deals with sets, or groups of things, and is used as the basis for data manipulation in the relational model.
Required attribute
In ER modeling, an attribute that must have a value. In other words, it cannot be left empty.
Optional attribute
In ER modeling, an attribute that does not require a value; therefore, it can be left empty.
Identifiers
The ERM uses one or more attributes that uniquely identify each entity instance.
Relational schema
The organization of a relational database as described by the database administrator.
Composite identifier
In ER modeling, a key composed of more than one attribute.
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.
Single-valued attribute
An attribute that can have only one value.
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.
Derived attribute
An attribute that does not physically exist within the entity and is computed via an algorithm.
Participants
An ER term for entities that participate in a relationship.
Connectivity
The classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.
Existence-dependent
A property of an entity whose existence depends on one or more other entities.
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.
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.
Weak (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.
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.
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.
Optional participation
In ER modeling, a condition in which one entity occurrence does not require a corresponding entity occurrence in a particular relationship.
Mandatory participation
A relationship in which one entity occurrence must have a corresponding occurrence in another entity.
Relationship degree
The number of entities or participants associated with a relationship. It can be unary, binary, ternary, or higher.
Unary relationship
An ER term used to describe an association within an entity. For example, an EMPLOYEE might manage another EMPLOYEE.
Binary relationship
An ER term for an association (relationship) between two entities. For example, PROFESSOR teaches CLASS.
Ternary relationship
An ER term used to describe an association (relationship) between three entities. For example, a DOCTOR prescribes a DRUG for a PATIENT.
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. [Show Less]