PMML 1.1 -- Data Dictionary
The data dictionary contains definitions for fields as used
in mining models.
It specifies the types and value ranges. These definitions are assumed to
be independent of specific data sets as used for training or building a
specific model.
A data dictionary can be shared by multiple models, statistics and other
information related to the training set is stored within a model;
see also the DTDs for
statistics
and
mining fields
.
<!ENTITY % FIELD-NAME "CDATA" > <!ELEMENT DataDictionary (Extension*, DataField+) > <!ATTLIST DataDictionary numberOfFields %INT-NUMBER; #IMPLIED > <!ELEMENT DataField ( Extension*, (Interval*| Value*) ) > <!ATTLIST DataField name %FIELD-NAME; #REQUIRED displayName CDATA #IMPLIED optype ( categorical | ordinal | continuous ) #REQUIRED isCyclic ( 0 | 1 ) "0" >
The fields are separated into different types depending on which operations are defined on the values; this is defined by the attribute optype. Categorical fields have the operator "=", ordinal fields have an additional "<", and continuous fields also have arithmetic operators. Cyclic fields have a distance measure which takes into account that the maximal value and minimal value are close together.
The content of a DataField defines the set of values which are considered to be valid.
Mining models distinguish three properties of values:
- Missing value:
- Input value is missing, for example, if a database column contains a null value. It is possible to explicitly define values which are interpreted as missing values.
- Invalid value:
- The input value is not missing but it does not belong to a certain value range. The range of valid values can be defined for each field.
- Valid value:
- A value which is neither missing nor invalid.
The following element definitions for Value and Interval are used to define the types and value ranges for fields in the data dictionary. The range of valid values can either be defined by specifying the set itself or by specifying complement set.
Note that PMML does not define how an interpreter of a model actually represents invalid or missing values. This depends on the application environment.
A continuous field may have at most
two intervals defining the range of valid values.
If intervals are present, any data that is outside the intervals
will be considered invalid.
If no intervals are present, the entire real
axis (except for discrete missing values) is made of valid values.
Intervals are not allowed for non-continuous fields
There can be continuous fields where a sequence
of valid values is specified instead of an interval range.
This can be used, for example, in a rating system
with a fixed set of values 1,2,3,4,5,6 representing grades.
Other values than
these numbers are considered as invalid input,
but the operational type still allows to compute sums and mean values.
Note that binary fields are modelled as categorical fields
where the value range
is given and it contains exactly two valid values.
There is no special
optype
value for binary fields.
Ordinal and continuous fields may be cyclic;
these are used for clustering models
where the distance of values depends on the 'cyclic' property.
For cyclic ordinal fields the sequence of
Value
elements also defines the first and last value of a cycle.
For continuous fields there must be exactly one interval of valid values,
this interval also defines the first and last value of a cycle.
The ordering for ordinal fields can be specified by a sequence of
category elements.
If the ordering is not specified in the element then the default ordering
on the representation type (strings, date, numbers, etc)
also defines the ordering of the field values in the mining model.
If the application algorithm for some class of models does not
require any special treatment of ordinal fields, then they
can be interpreted as categorical fields.
<!ELEMENT Value (Extension*) > <!ATTLIST Value value CDATA #REQUIRED displayValue CDATA #IMPLIED property (valid | invalid | missing ) "valid" >
The element Interval defines a range of numeric values.
<!ELEMENT Interval EMPTY> <!ATTLIST Interval closure (openClosed | openOpen | closedOpen | closedClosed ) #REQUIRED leftMargin %NUMBER; #IMPLIED rightMargin %NUMBER; #IMPLIED >