Inf282 Chapter 3 Relational Database Model

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associative entity

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also known as composite entity

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bridge entity

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also known as a composite entity

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candidate key

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a minimal super key that does not contain a subset of attributes that is itself a super key

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closure

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a property of relational operators that permits the use of relational algebra operators on existing tables/relations to produce new relations

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composite entity

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an entity designed to transform a M

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composite key

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a multiple attribute key

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data dictionary

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a DBMS component that stores metadata. Thus the data dictionary contains the data definition as well as its characteristics and relationships. A data dictionary may also include data that are external to the DBMS. Also known as an information resource dictionary.

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Determination

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the role of a key. The context of a database table, the statement “A determines B” indicates that knowing/determining the value of attribute A means that the value of attribute B can be looked up/determined

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domain

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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

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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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equijoin

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a join operator that links tables based on an equality condition that compares specified columns of the tables

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flags

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special codes implemented by designers to trigger a required response, to alert end users to specified conditions, or to encode values. Flags may be used to prevent nulls by bringing attention to the absence of a value in the table.

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foreign key

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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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full functional dependence

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A condition in which an attribute is functionally dependent on a composite key but not on any subset of that composite key.

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functional dependence

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Within a relation R, an attribute B is functionally dependent on an attribute A if and only if a given value of the attribute A determines exactly one value of the attribute B. The relationship “B is dependent on A” is equivalent to “A determines B” and is written as A→B

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homonyms

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Indicates the use of the same name to label different attributes

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Index

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An ordered array of index key values and row ID values (pointers). Indexes are generally used to speed up and facillitate data retrieval. Also known as an index key.

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index key

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index

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join column(s)

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A term used to refer to the columns that join two tables. The join columns generally share similar values.

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Key

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An entity identifier based on the concept of functional dependence, may be classified as follows, superkey, candidate key, primary key, secondary key, and foreign key

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key attribute

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The attributes that form a primary key. See also prime attribute.

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left outer join

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In a pair of tables to be joined a left outer join yields all of the rows in the left table, including those that have no matching values in the other table. For example, a left outer join of Customer with Agent will yield all of the Customer rows, including the ones that do not have a matching Agent row. See also outer join and right outer join.

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linking table

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In the relational model, a table that implements a M:M relationship. See also composite entity.

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natural join

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A relational operation that links tables by selecting only the rows with common values in their common attributes.

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Null

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in SQL, refers to the absence of an attribute value. Note: A null is NOT a blank.

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outer join

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A relational-algebra JOIN operation that produces a table in which all unmatched pairs are retained, unmatched values in the related table are left null. Contrast with inner join. See also left outer join and right outer join.

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predicate logic

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Used extensively in mathematics, provides a framework in which an assertion (statement of fact) can be verified as either true or false. For example, suppose that a student with a student ID of 12345678 is named Melissa. That assertion can easily be demonstrated to be true or false.

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primary key

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A candidate key selected as the unique entity identifier.

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referential integrity

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A condition by which a dependent table’s foreign key must either has a null entry or a matching entry in the related table. Even though an attribute may not have a corresponding attribute, it is impossible to have an invaild entry.

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relational algebra

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A set of mathematical principles that form the basis of the manipulation of relational table contents, composed of eight main functions, SELECT, PROJECT, JOIN, INTERSECT, UNION, DIFFERENCE, PRODUCT, and DIVIDE.

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relational schema

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The description of the organization of a relational database as seen by the database administrator.

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right outer join

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In a pair of tables to be joined, a right outer join yields all of the rows in the right table, including the ones with no matching values in the outer table. For example, a right outer join of CUSTOMER with AGENT will yield all of the agent rows, including the ones that do not have a matching CUSTOMER row. See also left outer join and outer join.

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secondary key

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A key that is used strictly for data retrieval purposes.

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set theory

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A mathematical science component that deals with sets, or gorups of things, and is used as the basis for data manipulation in the relational model.

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Superkey

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An attrbute that uniquely identifies each entity in a table.

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synonym

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The use of different names to identify the same object, such as entity, an attribute, or a relationship, should generally be avoided. See also homonym.

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system catalog

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A detailed system data dictionary that describes all objects in a database.

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theta join

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A join operator that links tables, using an inequality comparison operator (<, >, <=, >=) in the join condition.

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Tuple

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The the relational model, a table row.

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Union-compatible

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Two or more tables are union-compatible whent hey share the same column names and the columns have compatible data types or domains.

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unique index

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An index in which the index key can have only one pointer value associated with it.