Vision Class: Classification

Classification Overview

The Classification class is an abstract class used to organize a number of subclasses that define instances used for grouping and summarization purposes. Instances of Classification subclasses are normally referenced by other Entity instances. For example, the property country could be define for the class Company to return an instance of the Country class representing the country in which the company is based and the property industry could be defined to return an instance of the class Industry representing the company's major industry.

The Classification class is a direct subclass of Entity: 

  Object
     |
  Entity
     |
     Classification
        |
        |-- RangeClassification

The class Classification is used to unify all the protocol that is common to classifications. Your installation may define any number of subclasses of Classification. To determine which subclasses have been defined, use the expression: 

  Classification showInheritance

Basic Usage

The standard messages are used to create new subclasses, instances, and messages for the Classification subclasses. For example, to define a new subclass and some instances representing countries and a property that links specific currencies to specific countries, use the following: 

  #--  Define the new class and some instances
  Classification createSubclass: "Country" ;
  Country createInstance: "US" . 
     setNameTo: "Unites States" ;
  Country createInstance: "CA" .
     setNameTo: "Canada" ;

  #--  Define a message at Currency that returns country
  Currency defineFixedProperty: 'country' ;
  Named Currency USD :country <- Named Country US ;
  Named Currency CAD :country <- Named Country CA ;

Instances of many classification subclasses are often managed as a hierarchy. For example, Industry 123 may refer to "Book Publishing", Industry 120 may refer to "General Publishing", and Industry 100 may refer to "General Media". It is often useful to be able to link these instances. The property parent is defined at Classification and is used to store a reference to another instance of the class that represents the parent instance. The message setParentTo: allows you to set up these relationships. For example: 

  #--  Create Industry subclass
  Classification createSubclass: "Industry" ;

  #--  Create Industry instances and link to parent industry
  Industry createInstance: "100" . 
      setNameTo: "General Media" ;
  Industry createInstance: "120" . 
      setNameTo: "General Publishing" .
      setParentTo: Named Industry \100 ;
  Industry createInstance: "123" . 
      setNameTo: "Book Publishing" .
      setParentTo: Named Industry \120 ;
The expression: 
  Named Industry \123 parent name
accesses the name of industry 123's parent, "General Publishing". The message displayHierarchy displays the industry hierarchy: 
  Named Industry \123 displayHierarchy
produces: 
   123       Book Publishing
      120       General Publishing
         100       General Media

When new instances are created, the parent property is initialized to return the new instance. The isParent message returns TRUE if the recipient is its own parent instance.

The RangeClassification Class

The class RangeClassification has been created to manage classes whose instances are used to assign values falling into a particular numeric range. Instances are not directly created for this class; instead, you would create subclasses of RangeClassification for each distinct range being tracked. Instances of subclasses of RangeClassification define the properties lowerBound and upperBound. The message getClassificationFor: inputValue is used to access the instance whose range contains the supplied value. The message rangeName returns a string formatted as: 

  (lowerBound, upperBound)
For example, you can create a class to track market capitalization ranges using: 
  RangeClassification createSubclass: "MCapGroup"
New instances are created by supplying the lower and upper boundary values to the createInstance: message. NA values are used to indicate that a lower or upper bound is undefined: For example, you can create the instances for MCapGroup using: 
  MCapGroup
    createInstance: NA, 400 .
    setNameTo: "less than $400M" ;
  MCapGroup
    createInstance: 400, 1000 .
    setNameTo: "$400M - $1,000M" ;
  MCapGroup
    createInstance: 1000, 2000 .
    setNameTo: "$1,000M - $2,000M" ;
  MCapGroup
    createInstance: 2000, 5000 .
    setNameTo: "$2,000M - $5,000M" ;
  MCapGroup
    createInstance: 5000, NA .
    setNameTo: "greater than $5,000M" ;
The expression: 
  MCapGroup getClassificationFor: 2300
returns the instance represented by the range 2000,5000 . Selection is done using: 
  inputValue >= lowerBound && inputValue < upperBound
Assume that the property marketCap is defined for the class Security to return a numeric value. For reporting purposes you may want to group your securities into their market capitalization range and display summary data for each group. For example: 
  Security masterList
  extendBy: 
    [ !mcapGroup <- 
         ^global MCapGroup getClassificationFor: marketCap ;
    ] .
  groupedBy: [ mcapGroup ] .
  do: [ name print: 30 ; 
        groupList count print ;
        groupList min: [ marketCap ] . print ; 
        groupList max: [ marketCap ] . printNL ;
      ] ;

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