The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F...
In computer science, a data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently.Different kinds of data structures are suited to different kinds of applications, and some are highly specialized to specific tasks...
In computer science, a set is an abstract data structure that can store certain values, without any particular order, and no repeated values. It is a computer implementation of the mathematical concept of a finite set...
Edgar Frank "Ted" Codd was an English computer scientist who, while working for IBM, invented the relational model for database management, the theoretical basis for relational databases...
In mathematics, a binary relation on a set A is a collection of ordered pairs of elements of A. In other words, it is a subset of the Cartesian product A2 = . More generally, a binary relation between two sets A and B is a subset of...
In logic, mathematics, and computer science, the arity of a function or operation is the number of arguments or operands that the function takes. The arity of a relation is the dimension of the domain in the corresponding Cartesian product...
relation. Relation is a fundamental concept in relational model.
In relational databases, a relvar is a term coined by C. J. Date as an abbreviation for the concept of relation variable, which is the actual term used by the inventor of the relational model, E. F. Codd, regarding the same concept...
is a variable which has a relation value.
In some context, relation means relation variable. In another context, relation means relation value.
A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
In relational databases and flat file databases, a table is a set of data elements that is organized using a model of vertical columns and horizontal rows. A table has a specified number of columns, but can have any number of rows...
.
A relation value, which is assigned to a certain relation variable, is time-varying. By using a Data Definition Language
Data Definition Language
A data definition language or data description language is a syntax similar to a computer programming language for defining data structures, especially database schemas.-History:...
In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed....
. A heading has zero or more attributes.
A body is the unordered set of tuples, which constitutes a relation value. In other words, a relation value consists of a heading and a body.
A tuple is a data structure which consists of the unordered set of zero or more attributes.
In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed....
In data management and database analysis, a data domain refers to all the unique values which a data element may contain. The rule for determining the domain boundary may be as simple as a data type with an enumerated list of values....
In computer programming, a data type is a classification identifying one of various types of data, such as floating-point, integer, or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values of...
, or simply, type.
An attribute has an attribute value which conforms to its domain. An attribute value is a scalar value
Scalar (computing)
In computing, a scalar variable or field is one that can hold only one value at a time; as opposed to composite variables like array, list, hash, record, etc. In some contexts, a scalar value may be understood to be numeric. A scalar data type is the type of a scalar variable...
In grammar, the comparative is the form of an adjective or adverb which denotes the degree or grade by which a person, thing, or other entity has a property or quality greater or less in extent than that of another, and is used in this context with a subordinating conjunction, such as than,...
of a relation is the number of attributes which constitute a heading. The degree of a relation value is zero or more integer. An n-ary relation is a relation value in which its degree is n.
The cardinality of a relation is the number of tuples which constitutes a relation value. The cardinality of a relation value is zero or more integer.
There are no duplicate tuples in a relation value.
A candidate key
Candidate key
In the relational model of databases, a candidate key of a relation is a minimal superkey for that relation; that is, a set of attributes such that# the relation does not have two distinct tuples In the relational model of databases, a candidate key of a relation is a minimal superkey for that...
is a certain minimal set of one or more attributes that can uniquely identify individual tuples in a relation value.
Examples
The following is an example of a heading which consists of three attribute
Column (database)
In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed....
In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed....
In data management and database analysis, a data domain refers to all the unique values which a data element may contain. The rule for determining the domain boundary may be as simple as a data type with an enumerated list of values....
In computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....
In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....
Address : String
The following is an example of a relation value which consists of the above heading and tuples (row
Row (database)
In the context of a relational database, a row—also called a record or tuple—represents a single, implicitly structured data item in a table. In simple terms, a database table can be thought of as consisting of rows and columns or fields...
s) which conform to the heading.
This example shows a relation value in visual table
Table (database)
In relational databases and flat file databases, a table is a set of data elements that is organized using a model of vertical columns and horizontal rows. A table has a specified number of columns, but can have any number of rows...
form for the sake of convenience.
ID : Integer
Name : String
Address : String
102
"YONEZAWA Akinori"
"Naha, Okinawa"
202
"MURATA Makoto"
"Sendai, Miyagi"
104
"SAKAMURA Ken"
"Kumamoto, Kumamoto"
152
"MATSUMOTO Yukihiro"
"Okinawa, Okinawa"
The above relation value includes four tuples which share the same type.
As mentioned above, the attributes are unordered.
In other words, it is wrong to say "Address is on Name's right." and it is also wrong to say "Address is the third attribute."
As mentioned above too, the tuples are unordered.
In other words, it is wrong to say "The tuple of 'MURATA Makoto' is above the tuple of 'MATSUMOTO Yukihiro'" and it is also wrong to say "The tuple of 'YONEZAWA Akinori' is the first tuple."
Base relation variable and derived relation variable (view)
In relational databases, a relvar is a term coined by C. J. Date as an abbreviation for the concept of relation variable, which is the actual term used by the inventor of the relational model, E. F. Codd, regarding the same concept...
are classified into the two classes, which are base relation variable and derived relation variable.
By applying a relational algebra
Relational algebra
Relational algebra, an offshoot of first-order logic , deals with a set of finitary relations that is closed under certain operators. These operators operate on one or more relations to yield a relation...
Relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries...
expression to one or more relation variable, one new relation value is derived.
A base relation variable is a source relation variable which is not derived from any other relation variables.
In SQL
SQL
SQL is a programming language designed for managing data in relational database management systems ....
A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
In relational databases and flat file databases, a table is a set of data elements that is organized using a model of vertical columns and horizontal rows. A table has a specified number of columns, but can have any number of rows...
A data definition language or data description language is a syntax similar to a computer programming language for defining data structures, especially database schemas.-History:...
(DDL), it is able to define base relation variables.
In SQL, by using CREATE TABLE syntax, it is able to define base relation variables.
The following is an example.
CREATE TABLE List_of_people (
ID INTEGER,
Name CHAR(40),
Address CHAR(200),
PRIMARY KEY (ID)
)
A derived relation variable is a relation variable which is derived from one ore more relation variables by applying a relational algebra
Relational algebra
Relational algebra, an offshoot of first-order logic , deals with a set of finitary relations that is closed under certain operators. These operators operate on one or more relations to yield a relation...
Relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries...
In database theory, a view consists of a stored query accessible as a virtual table in a relational database or a set of documents in a document-oriented database composed of the result set of a query or map and reduce functions...
is considered derived relation variable.
By using a Data Definition Language (DDL), it is able to define derived relation variables.
In SQL, by using CREATE VIEW syntax, it is able to define derived relation variables.
The following is an example.
CREATE VIEW List_of_Okinawa_people AS (
SELECT ID, Name, Address
FROM List_of_people
WHERE Address LIKE '%, Okinawa'
)
In set theory and logic, a relation is a property that assigns truth values to k-tuples of individuals. Typically, the property describes a possible connection between the components of a k-tuple...
In data management and database analysis, a data domain refers to all the unique values which a data element may contain. The rule for determining the domain boundary may be as simple as a data type with an enumerated list of values....
In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed....
A data model in software engineering is an abstract model, that documents and organizes the business data for communication between team members and is used as a plan for developing applications, specifically how data is stored and accessed....
Data modeling in software engineering is the process of creating a data model for an information system by applying formal data modeling techniques.- Overview :...
Data management comprises all the disciplines related to managing data as a valuable resource.- Overview :The official definition provided by DAMA International, the professional organization for those in the data management profession, is: "Data Resource Management is the development and execution...
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
Database design is the process of producing a detailed data model of a database. This logical data model contains all the needed logical and physical design choices and physical storage parameters needed to generate a design in a Data Definition Language, which can then be used to create a database...
In the design of a relational database management system , the process of organizing data to minimize redundancy is called normalization. The goal of database normalization is to decompose relations with anomalies in order to produce smaller, well-structured relations...
In relational database design, a unique key can uniquely identify each row in a table, and is closely related to the Superkey concept. A unique key comprises a single column or a set of columns. No two distinct rows in a table can have the same value in those columns if NULL values are not used...
In the relational model of databases, a candidate key of a relation is a minimal superkey for that relation; that is, a set of attributes such that# the relation does not have two distinct tuples In the relational model of databases, a candidate key of a relation is a minimal superkey for that...
The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F...
A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
A relational database management system is a database management system that is based on the relational model as introduced by E. F. Codd. Most popular databases currently in use are based on the relational database model....
Query languages are computer languages used to make queries into databases and information systems.Broadly, query languages can be classified according to whether they are database query languages or information retrieval query languages...
A data definition language or data description language is a syntax similar to a computer programming language for defining data structures, especially database schemas.-History:...
D is a set of requirements for what Christopher J. Date and Hugh Darwen believe a relational database query language ought to be like. It is proposed in their book The Third Manifesto.-Overview:...
Tutorial D
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A relation value, which is assigned to a certain relation variable, is time-varying. By using a Data Definition Language