101companies

Headline

Construction of data according to variants

Note

Data variation is not an established term, but it naturally arises as a generalization and dualization of existing notions that are used in data modeling and programming. Common forms of data variation are based on variant types and type generalization. For clarity, the general term data variation is used on this wiki, whenever appropriate.

Description

Data variation entails data variants, of which one must be chosen when actual data is constructed. The data variants may be specified, for example, as a variant type or as OO types related to a common base type through type generalization. Data variation may be seen as a principle means of going beyond data composition.

Illustration

The following Language:Haskell-based data model for the @system leverages data variation in one spot and otherwise data composition. The data model is based on algebraic data types. The data type for subunits declare two constructors to model different types of subunits, as needed for aggregating subunits of departments. 

data Company = Company Name [Department]
data Department = Department Name Manager [SubUnit]
data Employee = Employee Name Address Salary
data SubUnit = EUnit Employee | DUnit Department
type Manager = Employee
type Name = String
type Address = String
type Salary = Float

The snippet originates from Contribution:haskellVariation.

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