Representations

Representations describe the structure and content of data as it is captured from the population and held within a data file. They share common category schemes and code list as well as the means of defining numeric ranges and text content. DDI begins by defining the core descriptive content for a wide range of representations and then adds a set of common objects used by all Value Representations (Variables) or Response Domains (Questions) in their applied use.

A number of these representations also have a Managed version which allows a single description of a Representation to be reused within and between studies. Some Representations reference reusable structures (Category Schemes, Code Lists, etc.) and are already reusable. Others such as Numeric Representations have a Managed Representation contained in a ManagedRepresentationScheme located in Logical Product. This Scheme contains all forms of Managed Representations and supports the standard Scheme organizational objects that allow for grouping and classification according to Subjects, Keywords, Concept, and Universe

Whether you provide representations inline or manage them within a scheme, they contain the same information. High level descriptions are shown below, detailed explanations are described in the Specific Structures section.

Variables use the representation substitutions found in reusable directly as substitution types for VariableRepresentation with the exception of CodeRepresentation where it allows additional specifications of the use of the CodeScheme contents. Further explanation of this can be found in the Value Representation section.

QuestionItem uses local substitution types for ResponseDomain which use their respective representation types with the addition of an optional Label and Description. Questions that require a mixture of response domain types may do so by using the StructuredMixedResponseDomain as an alternative to ResponseDomain. Further explanation of this can be found in the Response Domain section.

Each representation type described below notes the related ResponseDomain and VariableRepresentation including any details of specialized use.

All representation types provide the following optional content that help to define the classification and use of the representation content. When used as question response domains these may not be relevant, however, depending on the type of response domain the user may wish to define this content.

RecommendedDataType This element is a CodeValueType which allows for input of a simple term or reference to an established controlled vocabulary list. Preferably the user should select from the W3C XML Schema Part 2 list of data types with the exception of sub-string types QNAME and NOTATION. See: http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#built-in-datatypes
GenericOutputFormat This element is a CodeValueType which allows for input of a simple term or reference to an established controlled vocabulary list. This element provides specification for the preferred output format expressed in a generic way.
@missingValue Provides a listing as a space delimited array of values that should be treated as missing values.
@blankIsMissingValue A Boolean attribute that when set to ‘true’, indicates that a blank (no content) should be treated as a missing value.
@classificationLevel Indicates the classification of the content as: Nominal, Ordinal, Interval, Ratio, or Continuous

Representation (inline)

Figure 4. Overview of Representation (inline)

figure4

Available Inline Representation members

Variable Representation Question Representation
TextRepresentation TextDomainType
DateTimeRepresentation DateTimeDomainType
NumericRepresentation NumericDomainType
ExternalCategoryRepresentation ExternalCategoryDomainType
CodeRepresentation CodeDomainType
ScaleRepresentation ScaleDomainType
GeographicLocationCodeRepresenation GeographicLocationCodeRepresenation
GeographicStructureCodeRepresentation GeographicStructureCodeDomainType
  CategoryDomainType
  GeographicDomainType
  NominalDomainType
  LocationDomainType
  RankingDomainType
  DistributionDomainType

Comparison of Inline Value Representation and Response Domains

Variable representation Question representation
TextRepresentation TextDomain

RecommendedDataType

GenericOutputFormat

@missingValues

@blankIsMissingValue

@classificationLevel

@maxLength

@minLength

@regExp

RecommendedDataType

GenericOutputFormat

@missingValues

@blankIsMissingValue

@classificationLevel

@maxLength

@minLength

@regExp

Label

Description

OutParameter

ResponseCardinality

ContentDateOffset

CodeRepresentation CodeDomain

RecommendedDataType

GenericOutputFormat

@missingValues

@blankIsMissingValue

@classificationLevel

CodeListReference

CodeSubsetInformation

RecommendedDataType

GenericOutputFormat

@missingValues

@blankIsMissingValue

@classificationLevel

CodeListReference

CodeSubsetInformation

Label

Description

OutParameter

ResponseCardinality

ContentDateOffset

Representation (by Reference)

Figure 5. Overview of Representation (by reference)

figure5

Available Managed Representation members

Variable Representation Question Representation
TextRepresentationReference TextDomainReference
DateTimeRepresentationReference DateTimeDomainReference
NumericRepresentationReference NumericDomainReference
ScaleRepresentationReference ScaleDomainReference
  MissingValuesDomainReference

Comparison of Managed Value Representation and Response Domains