Data domain - AbsoluteAstronomy.com

Data management

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...

and database

Database

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...

analysis, a data domain refers to all the unique values which a data element

Data element

In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has:# An identification such as a data element name# A clear data element definition# One or more representation terms...

may contain. The rule for determining the domain boundary may be as simple as a data type

Data type

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...

with an enumerated

Enumeration

In mathematics and theoretical computer science, the broadest and most abstract definition of an enumeration of a set is an exact listing of all of its elements . The restrictions imposed on the type of list used depend on the branch of mathematics and the context in which one is working...

list of values.

For example, a database

Database

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...

that has information about people, with one record per person, might have a "gender

Gender

Gender is a range of characteristics used to distinguish between males and females, particularly in the cases of men and women and the masculine and feminine attributes assigned to them. Depending on the context, the discriminating characteristics vary from sex to social role to gender identity...

" column

Column

A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

. This gender column might be declared as a string data type, and allowed to have one of two known code values

Code (metadata)

In metadata, the representation term code refers to, and is used in the name of, data elements whose allowable values can be represented as enumerated lists. Each enumerated value is a string that for brevity represents a specific meaning. For example, for a PersonGenderCode the allowable code...

: "M" for male, "F" for female—and NULL

Null (SQL)

Null is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfill the requirement that all true relational database management systems support...

for records where gender is unknown or not applicable (or arguably "U" for unknown as a sentinel value

Sentinel value

In computer programming, a sentinel value is a special value whose presence guarantees termination of a loop that processes structured data...

). The data domain for the gender column is: "M", "F".

In a normalized

Database normalization

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...

data model

Data model

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....

, the reference domain

Master Data Management

In computing, master data management comprises a set of processes and tools that consistently defines and manages the non-transactional data entities of an organization...

is typically specified in a reference table

Reference table

A reference table may mean a set of references that an author may have cited or gained inspiration from whilst writing an article, similar to a bibliography....

. Following the previous example, a Gender reference table would have exactly two records, one per allowed value—excluding NULL. Reference tables are formally related to other tables in a database by the use of foreign key

Foreign key

In the context of relational databases, a foreign key is a referential constraint between two tables.A foreign key is a field in a relational table that matches a candidate key of another table...

s.

Less simple domain boundary rules, if database-enforced, may be implemented through a check constraint

Check Constraint

A check constraint is a condition that defines valid data when adding or updating an entry in a table of a relational database. A check constraint is applied to each row in the table. The constraint must be a predicate. It can refer to a single or multiple columns of the table...

or, in more complex cases, in a database trigger

Database trigger

A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. The trigger is mostly used for keeping the integrity of the information on the database...

. For example, a column requiring positive numeric values may have a check constraint declaring that the values must be greater than zero.

This definition combines the concepts of domain as an area over which control is exercised and the mathematical idea of a set of values of an independent variable

Independent variable

The terms "dependent variable" and "independent variable" are used in similar but subtly different ways in mathematics and statistics as part of the standard terminology in those subjects...

for which a function

Function (mathematics)

In mathematics, a function associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output. A function assigns exactly one output to each input. The argument and the value may be real numbers, but they can...

is defined. See: domain (mathematics)

Domain (mathematics)

In mathematics, the domain of definition or simply the domain of a function is the set of "input" or argument values for which the function is defined...

See also