GLOSSARY

This appendix contains a glossary of useful database terms. You may find them handy when you read other books and articles about databases. You may also want to look for database and related glossaries online and in print. For example, https://raima.com/database-terminology and www.prisma.io/dataguide/intro/database-glossary provide good online glossaries.

1NF
See first normal form.
2NF
See second normal form.
3NF
See third normal form.
4NF
See fourth normal form.
5NF
See fifth normal form.
6NF
See domain key normal form.

A

ACID
An acronym for a set of database properties needed for reliable transactions. ACID stands for atomicity, consistency, isolation, durability (see the entries for those terms).
alternate key
A candidate key that is not used as the table's primary key.
Apache Ignite
A NoSQL key-value database that can run locally or in the cloud. See https://ignite.apache.org.
association object
In a semantic object model, an object used to represent a relationship between two other objects.
atom
A piece of data that cannot be meaningfully divided. For example, a Social Security number of the form 123-45-6789 contains three pieces. There is structure in those pieces (see www.ssa.gov/history/ssn/geocard.html), but it's a pretty unusual application that needs to look them up separately so the number as a whole is usually treated as an atom.
atomic transaction
A possibly complex series of actions that is considered as a single operation by those not involved directly in performing the transaction.
atomicity
The requirement that tasks within a transaction occur as a group as if they were a single complex task. The tasks are either all performed or none of them are performed. It's all or nothing.
attribute
The formal database term for column (see column).

B

b+tree
(Pronounced “bee plus tree.”) A self-balancing tree data structure that allows efficient searching of indexes. A b+tree stores data records only in leaf nodes.
BCNF
See Boyce-Codd normal form.
BLOB
Binary large object. A data type that can hold large objects of arbitrary content such as video files, audio files, images, and so forth. Because the data can be any arbitrary chunk of binary data, the database does not understand its contents so you cannot search in these fields.
Boyce-Codd normal form (BCNF)
A table is in BCNF if every determinant is also a candidate key (minimal superkey). See determinant and candidate key.
b-tree
(Pronounced “bee tree.”) A self-balancing tree data structure that allows efficient searching of indexes. A b-tree stores data records in internal and leaf nodes.
business rule
Business-specific rule that constrains the data. For example, “all orders require a valid existing Customers record” and “orders for $50 or more get free shipping” are business rules.

C

candidate key
A minimal superkey (see superkey). In other words, the fields in a candidate key uniquely define the records in a table and no subset of those fields also uniquely defines the records.
cardinality
A representation of the minimum and maximum allowed number of values for an attribute. In semantic object models, written as L.U, where L and U are the lower and upper bounds. For example, 1.10 means an attribute must occur between 1 and 10 times.
catalog
A directory storing metadata.
check constraint
A record-level validation that is performed when a record is created or updated.
cloud
Servers, software, databases, and services that are accessed over the Internet.
column
A piece of data that may be recorded for each row in a table. The corresponding formal database term is attribute.
column-oriented database (aka wide-column database or column family database)
These allow you to treat data in a table-like format, although they may allow different rows in a table to contain different fields. They are optimized to efficiently fetch or search data in columns, so they make aggregation analysis faster.
commit
To make changes performed within a transaction permanent. The SQL COMMIT command performs this action.
composite index
An index that includes two or more fields. Also called a compound index or concatenated index.
composite key
A key that includes two or more fields. Also called a compound key or concatenated key.
composite object
In a semantic object model, an object that contains at least one multivalued, non-object attribute.
compound index
An index that includes two or more fields. Also called a composite index or concatenated index.
compound key
A key that includes two or more fields. Also called a composite key or concatenated key.
compound object
In a semantic object model, an object that contains at least one object attribute.
concatenated index
An index that includes two or more fields. Also called a compound index or composite index.
concatenated key
A key that includes two or more fields. Also called a compound key or composite key.
consistency
The requirement that a transaction should leave the database in a consistent state. If a transaction would put the database in an inconsistent state, the transaction is canceled.
CRUD
An acronym for the four main database operations: create, read, update, delete. These operations correspond to the SQL statements INSERT, SELECT, UPDATE, and DELETE.
CSV file
Comma-separated value file. A text file where each row contains the data for one record and field values are separated by commas.
cursor
An object that allows a program to work through the records returned by a query one at a time. Some databases allow cursors to move forward and backward through the set of returned records, whereas others allow only forward movement.
cyclic dependency
Occurs when objects depend on each other directly or indirectly. For example, a cyclic dependency occurs in a table if field A depends on field B, field B depends on field C, and field C depends on field A.

D

Data Control Language (DCL)
The SQL commands that control access to data such as GRANT and REVOKE.
Data Definition Language (DDL)
The SQL commands that deal with creating the database's structure such as CREATE TABLE, CREATE INDEX, and DROP TABLE.
data dictionary
A list of descriptions of data items to help developers stay on the same track.
Data Manipulation Language (DML)
The SQL commands that manipulate data in a database. These include INSERT, SELECT, UPDATE, and DELETE.
data mart
A smaller data warehouse that holds data of interest to a particular group. Also see data warehouse.
data mining
Digging through data (usually in a data warehouse or data mart) to identify interesting patterns.
data scrubbing
Processing data to remove or repair inconsistencies.
data type
The type of data that a column can hold. Types include numbers, fixed-length strings, variable-length strings, BLOBs, and so forth.
data warehouse
A repository of data for offline use in building reports and analyzing historical data. Also see data mart.
database
An entity that holds data in some useful way and provides CRUD methods (see CRUD). Modern databases also provide sophisticated methods for joining, sorting, grouping, and otherwise manipulating the data.
database administrator (DBA)
Someone who manages the database, optimizes performance, performs backups, and so forth.
DBA
See database administrator.
DBMS
Database management system. A product or tool that manages any kind of database, not just relational databases.
DDBMS
Distributed database management system. See DBMS.
DDL
See Data Definition Language.
delete
To remove one or more rows from a table. The SQL DELETE command performs this action. Represents the D (for Delete) in CRUD.
deletion anomaly
Occurs when deleting a record can destroy information.
determinant
A field that at least partly determines the value in another field.
dimensional database
A database that treats the data as if it is stored in cells within a multidimensional array (see multidimensional array).
distributed database
A database with pieces stored on multiple computers on a network.
DKNF
See domain key normal form.
DML
See Data Manipulation Language.
document database (aka document store or document-oriented database)
Stores documents, usually in XML, JSON, BJSON, or a similar format. These allow you to query on fields defined within the documents.
domain
The values that are allowed for a particular column. For example, the domain of the AverageSpeed field in a database of downhill speed skiers might allow values between 0 and 200 miles per hour (although if your average speed is 0, you might consider another sport).
domain key normal form (DKNF)
A table is in DKNF if it contains no constraints except domain constraints and key constraints.
durability
The requirement that a completed transaction is safely recorded in the database and will not be lost even if the database crashes.

E

Easter egg
A feature or message hidden in software or another medium.
Edgar Codd
IBM researcher who laid the groundwork for modern relational databases and SQL starting in 1970.
edge
In a graph database, a connection between two nodes. An edge represents a relationship between its nodes, so it is sometimes called a relationship.
entity
In entity-relationship modeling, an object or item of interest such as a customer, invoice, vehicle, or product.
entity integrity
Requires that all tables have a primary key. The values in the primary key fields must be non-null and no two records can have the same primary key values.
entity-relationship diagram (ER diagram)
A diagram that shows entities (rectangles), their attributes (ellipses), and the relationships among them (diamonds).
ER diagram
See entity-relationship diagram.
Extensible Markup Language (XML)
A language that uses nested tokens to represent hierarchical data. Also see JSON.

F

field
Another informal term for column (see column).
fifth normal form (5NF)
A table is in 5NF if it is in 4NF and contains no related multivalued dependencies.
first normal form (1NF)
A table is in 1NF if it satisfies basic conditions to be a relational table.
flat file
A plain-old text file used to store data. A flat file isn't very fancy and provides few tools for querying, sorting, grouping, and performing other database operations, but flat files are very easy to use.
foreign key
One or more columns that are related to values in corresponding columns in another table.
fourth normal form (4NF)
A table is in 4NF if it is in BCNF and contains no unrelated multivalued dependencies.

G

graph database
A database that stores nodes that represent pieces of data connected by edges (aka links or relationships) that represent relationships between the nodes. These are good when you want to study relationships among objects.
Graph Query Language (GQL)
Upcoming standard language for querying graph databases. Used by Neo4j AuraDB. See www.gqlstandards.org.

H

HOLAP
Hybrid online analytical processing. A combination of MOLAP and ROLAP. Typically, this combines relational storage for some data and specialized storage for other data. The exact definition of HOLAP isn't clear, so you can use it as a conversation starter at cocktail parties. Also see OLAP.
hybrid object
In a semantic object model, an object that contains a combination of multivalued and object attributes.
hypercube
A multidimensional array (see multidimensional array). To be a true hypercube, each dimension should have the same length or number of entries.

I

identifier
In a semantic object model, one or more attributes that are used to identify individual objects. Indicated by writing ID to the left of the attribute(s), underlined if the identifier is unique.
index
A data structure that uses one or more columns to make looking up values on those columns faster.
insert
To create a new record in a table. The SQL INSERT command performs this action. The C (for Create) in CRUD.
insertion anomaly
Occurs when you cannot store certain kinds of information because it would violate the table's primary key constraints.
instance
A particular occurrence of an entity. For example, if VicePresident is an entity (class), then William Rufus King was an instance of that class.
isolation
The requirement that no one should be able to peek into the database and see changes while a transaction is underway. Anyone looking at the data will either see it as it is before the transaction or after the transaction but cannot see the transaction partly completed.

J

JavaScript Object Notation (JSON)
A language that uses nested tokens to represent hierarchical data. Also see XML.
join
A query that selects data from more than one table, usually using a JOIN or WHERE clause to indicate which records in the two tables go together.
JOLAP
Java Online Analytical Processing. A Java API for online analytical processing. Also see OLAP.
JSON
See JavaScript Object Notation.

K

key
One or more fields used to locate or arrange the records in a table. Also see index.
key constraint
In an ER diagram, a key constraint means an entity can participate in at most one instance of a relationship. For example, during flight a pilot can fly at most one hang glider.
key-value database (aka key-value store)
A database that holds values that you can index by using a key. This is similar to the hash tables, dictionaries, and associative arrays that are provided by different programming languages.

L

link
See edge.
lock
Used to control access to part of the database. For example, while one user updates a row, the database places a lock on the row so that other users cannot interfere with the update. Different databases may lock data by rows, table, or disk page.

M

many-to-many relationship
A relationship where one object of one type may correspond to many objects of another type, and vice versa. For example, one COURSE may include many STUDENTs and one STUDENT may be enrolled in many COURSEs. Normally you implement this kind of relationship by using an intermediate table that has one-to-many relationships with the original tables.
MariaDB
An open source relational database management system. See https://mariadb.org. Also see Michael Widenius.
MaxDB
Relational database management system from SAP AG. Also see Michael Widenius.
memo
A text data type that can hold very large chunks of text.
metabase
A database that stores metadata.
metadata
Data about the database such as table names, column names, column data types, column lengths, keys, and indexes. Some relational databases allow you to query tables that contain the database's metadata.
Michael Widenius
Main author of the MySQL, MariaDB, and MaxDB databases, which are named for his children My, Maria, and Max.
MOLAP
Multidimensional analytical processing. The “classic” version of OLAP and is sometimes referred to as simply OLAP. See OLAP.
MongoDB Atlas
A NoSQL cloud document database. See www.mongodb.com.
multidimensional array
A multidimensional rectangular block of cells containing values. Picture a row of bricks where each brick is a cell. A wall made of bricks arranged in rows and columns (which would not be very architecturally sound) would be a two-dimensional array. A series of walls closely packed together (which would be architecturally bizarre) would be a three-dimensional array. Use your imagination for higher dimensions.
multivalued dependency
When one field implies the values in two other fields that are unrelated. For example, a table has a multivalued dependency if field A implies values in field B, and field A implies values in field C, but the values in fields B and C are not related.
MySQL
A relational database management system that was formerly open source but that is now mostly commercialized. See www.mysql.com. Also see Michael Widenius.

N

Neo4j AuraDB
Fully managed graph database service in the cloud. See www.neo4j.com. Uses the Graph Query Language (see Graph Query Language).
node
In a graph database, a node represents some kind of object. Edges define relationships between nodes.
normalization
The process of transforming the database's structure to minimize the chances of certain kinds of data anomalies.
NoSQL
Either “not SQL” or “not only SQL.” When speaking about database types, this generally refers to nonrelational databases, which include the four main categories document database, key-value database, column-oriented database, and graph database. Many of these can run locally or in the cloud.
null
A special column value that means “this column has no value.”

O

object
An instance of an item of interest to the data model. See instance.
object database
See object-oriented database.
object database management system (ODBMS)
A product or tool for managing object-oriented databases. See object-oriented database.
object store
See object-oriented database.
object-oriented database
A database that provides tools to allow a program to create, read, update, and delete objects. The database automatically handles object persistence (changes to the object are automatically saved) and concurrency (two users accessing the same object will not interfere with each other).
object-relational database (ORD)
A database that provides relational operations plus additional features for creating, reading, updating, and deleting objects.
object-relational database management system (ORDBMS)
See object-relational database.
object-relational mapping
A translation layer that converts objects to and from entries in a relational database.
ODBMS
See object database management system.
OLAP
See online analytical processing.
one-to-many relationship
A relationship where one object of one type may correspond to many objects of another type. For example, one INSTRUCTOR may teach many COURSEs, but each COURSE has only one INSTRUCTOR.
one-to-one relationship
Occurs when one record in a table corresponds to exactly one record in another table. For example, each US_STATE has one GOVERNOR and each GOVERNOR belongs to one US_STATE.
online analytical processing (OLAP)
A data mining approach for analyzing information from multiple data sources.
OODBMS
Object-oriented database management system. See object database management system.
Oracle
An enterprise-level relational database management system. See www.oracle.com/database.
ORD
See object-relational database.
ORDBMS
Object-relational database management system. See object-relational database.

P

participation constraint
In an ER diagram, a participation constraint means every entity in an entity set must participate in a relationship set. The constraint is drawn with a thick or double line. For example, during flight a hang glider must participate in the “Pilot Flies HangGlider” relationship.
PL/SQL
Procedural Language/Structured Query Language. Oracle's extension to SQL used to write stored procedures in Oracle.
PostgreSQL (aka Postgres)
Open source object-relational database system. See www.postgresql.org.
primary key
A candidate key that is singled out as the table's “main” method for uniquely identifying records. Most databases automatically build an index for a table's primary key and enforce uniqueness.
primary key constraint
Requires that each table's primary key behavior be valid. In particular, this requires that no two records in a table have exactly the same primary key values and that all records' primary key values be non-null.

Q

query
A command that extracts data from a database. In SQL, a SELECT statement.

R

RDBMS
See relational database management system.
record
Another informal term for row (see row).
referential integrity
Requires that relationships among tables be consistent. For example, foreign key constraints must be satisfied. You cannot accept a transaction until referential integrity is satisfied.
regret
What you feel when you accidentally omit the WHERE clause in an UPDATE or DELETE statement so that you update or delete every record in the table.
relation
The database theoretical term for a table. For example, the Customer table is a relation holding attributes such as FirstName, LastName, Street, City, State, ZipCode, PacManTopScore, and WarcraftName.
relational database
A database that stores data in tables containing rows and columns and that allows queries representing relationships among records in different tables.
relational database management system (RDBMS)
A product or tool that manages a relational database such as MySQL, PostgreSQL, MariaDB, or SQL Server.
relationship
An association between two tables. For example, if an order contains several order items, there is a one-to-many relationship between the Orders and OrderItems tables. Don't confuse this term with “relation.”
replication
The process of storing data in multiple databases while ensuring that it remains consistent. For example, one database might contain a master copy of the data and other satellite databases might hold read-only copies to let clerks or customers view data quickly without impacting the main database.
report
The results of a query displayed in a nice format. Sometimes, this term is used to mean the format that will produce the report when data is added to it.
ROLAP
Relational online analytical processing. OLAP performed with a relational database. See OLAP.
roll back
To undo changes performed within a transaction before the transaction is committed. The SQL ROLLBACK command performs this action.
row
A group of related column values in a table. The corresponding formal database term is tuple. Also see record.

S

savepoint
A position within a transaction that you may want to roll back to later. The program can roll back the entire transaction or to a savepoint. The SQL SAVEPOINT command creates a savepoint.
second normal form (2NF)
A table is in 2NF if it is in 1NF and every field that is not part of the primary key depends on every part of the primary key.
select
To extract data from a database, possibly from multiple tables. The SQL SELECT command performs this action. This is the R (for Read) in CRUD.
semantic attribute
A characteristic of a semantic object.
semantic class
A named collection of attributes sufficient to specify an entity of interest.
semantic object (SO)
An instance of a semantic class with specific attribute values.
semantic object model (SOM)
A model that uses classes, objects, and relationships to provide understanding of a system. Classes have attributes that describe instances. Object attributes provide the relationships among objects.
simple object
In a semantic object model, an object that has only single-valued simple attributes.
SOM
See semantic object model.
splay tree
A self-balancing tree data structure that allows efficient searching of indexes.
SQL
See Structured Query Language.
SQL Server
Microsoft's enterprise-level relational database management system. See www.microsoft.com/sql.
stored procedure
A piece of code stored in the database that can be executed by other pieces of code such as check constraints or application code. Stored procedures are a good place to store business logic that should not be built into the database's structure.
Structured Query Language (SQL)
An industry standard English-like language for building and manipulating relational databases.
subclass object
An object that represents a subset of the objects in a larger class. For example, the Vehicle class could have a Truck subclass, which could have its own PickupTruck subclass, which could in turn have its own BrokenPickupTruck class.
superkey
A set of fields that uniquely define the records in a table. (Not a key that wears a cape and fights crime.)

T

table
A collection of rows holding similar columns of data. The corresponding formal database term is relation.
temporal database
A database that associates times with data. See valid time.
third normal form (3NF)
A table is in 3NF if it is in 2NF and it contains no transitive dependencies.
transaction
A series of database operations that should be treated as a single atomic operation, so either they all occur or none of them occur. In SQL a transaction normally begins with a START TRANSACTION or BEGIN TRANSACTION command and ends with a COMMIT or ROLLBACK command. Also see commit, roll back, and savepoint.
Transaction Control Language (TCL)
The SQL commands that control transactions such as COMMIT, ROLLBACK, and SAVEPOINT.
Transact-SQL (TSQL)
Microsoft's version of SQL used in SQL Server. See SQL.
transitive dependency
When one non-key field's value depends on another non-key field's value. Typically, this shows up as duplicated data. For example, suppose a table holds people's favorite book information and includes fields Person, Title, and Author. The primary key is Person but Title determines Author, so there is a transitive dependency between Title and Author.
trigger
A stored procedure that executes when certain conditions occur such as when a record is created, modified, or deleted. Triggers can perform special actions like creating other records or validating changes.
TSQL
See Transact-SQL.
tuple
The formal database term for a record or row (see row).

U

unique constraint (aka uniqueness constraint)
Requires that the values in one or more columns be unique within a table.
update
To modify the values in a record's fields. The SQL UPDATE command performs this action. This is the U (for Update) in CRUD.
update anomaly
Occurs when a change to a row leads to inconsistent data.

V

valid time
The time during which a piece of data is valid in a temporal database.
view
The result of a query that can be treated as if it were a virtual table. For example, you could define views that return only selected records from a table or that return only certain columns.

W

weak entity
In an ER diagram, an entity that cannot be identified by its own attributes. Instead you need to use the attributes of some other associated entity to find the weak entity. Drawn with a bold or double rectangle and attached to its identifying relationship by a bold or double arrow.

X

XML
See Extensible Markup Language (XML).
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