Classification
Each property within MDDL which is intended to convey data is defined by a classification. The classification clarifies the content the property holds and identifies a predetermined set of properties that may augment that content. It is used to denote the fundamental usage of a property. Classifications included in MDDL are the following:

Amount:
A property of classification Amount indicates a quantity of money for a transaction of more than one item. The value of an Amount is the value of the property of classification Price multiplied by the value of another property of classification Quantity.

Amount properties can be augmented by the following properties:
  calculationType   currency   dateTime   fraction   indicatorsType   marketCenter   multiplier   previousDateTime   sequence   source   valuationType   valuationRef

DateTime:
A property of classification DateTime can hold a date, time, or date and time as defined by the mdDateTime element.

DateTime properties can be augmented by the following properties:
  indicatorsType   marketCenter   sequence   source

Fee:
The classification Fee denotes a property that holds a quantity of money for the cost of a transaction or exchange of goods.

DateTime properties can be augmented by the following properties:
  calculationType   currency   dateTime   fraction   indicatorsType   marketCenter   previousDateTime   seqeunce   source   valuationType   valuationRef

Measure:
A property of classification Measure holds a number that represents a non-money based indicator or reference value.

Measure properties can be augmented by the properties:
  calculationType   dateTime   fraction   indicatorsType   marketCenter   multiplier   previousDateTime   seqeunce   source   valuationType   valuationRef

Quantity:
A property of classification Quantity holds a number that represents an accumulator or counting of some entity.

Quantity properties can be augmented by the properties:
  calculationType   dateTime   fraction   indicatorsType   marketCenter   multiplier   previousDateTime   seqeunce   source   valuationType   valuationRef

Price:
Properties of classification Price hold a number indicating a quantity of money for a single item.

Price properties can be augmented by the properties:
  calculationType   currency   dateTime   fraction   indicatorsType   marketCenter   multiplier   previousDateTime   seqeunce   size   source   valuationType   valuationRef

Container:
A property of classification Container does not have any content other than child elements. It is intended to hold other elements (as a placeholder) and hence does not have a base type associated with it.

Enumeration:
A property of classification Enumeration holds a String value constrained by the discrete values from a Controlled Vocabulary identified in the 'scheme' attribute. The value of the 'scheme' attribute points to file that contains the discrete list of values (or to a webservice that can validate them). Note that some schemes are assigned default values in the schema and thus they may not appear in an MDDL Instance Document.

Rate:
A property of classification Rate holds a decimal value representing a ratio or percentage value.

Rate properties can be augmented by the properties:
  calculationType   currency   dateTime   fraction   indicatorsType   marketCenter   multiplier   previousDateTime   seqeunce   source   valuationType   valuationRef

Root:
There is only one element within the MDDL schema that has a classification of 'root' - the root 'mddl' element!

Simple:
This identifies a property that has a base type but without explicitly defined modifiers. Note that a 'simple' property may still have qualifiers - but not from a predetermined set.

Adding Classifications
It is not recommended that any other classifications be added outside the formal specification review process. The basic classifications are fundamental to the recipient’s understanding and processing of the data. As such, MDDL does not support the addition of classifications without modification to the base schema. All requests for modifications or addition of classifications should be directed to the MDDL sponsoring agency.