DDI is a very flexible and complex standard, and even within the mappings from GSIM which have been developed, there is still the possibility that two GSIM implementations using DDI might not interoperate. DDI itself provides a mechanism for solving this problem – a feature of the standard known as “DDI Profiles”. It is thought that the publication of standard DDI profiles will facilitate the harmonisation of the use of DDI in statistical organisations.
What is a DDI Profile?
According to the DDI 3.2 documentation, a DDI profile “describes the subset of valid DDI objects used by an agency for a specified purpose.” This is documented in an XML format (part of the DDI specification) which allows a set of declarations to be made, identifying specific fields in the DDI which are “Used” or “Not Used”. Various other qualifications can be made to restrict or default permitted values for specific elements, and human-readable documentation can be added.
Thus, an organization or application can specify exactly how it uses the DDI XML formats. It is anticipated that as organizations implement GSIM, these standard profiles can be used to form a base set of DDI elements for interoperable use.
Examples of some of the profileswhich have been developed include:
- BTO Profile: The first profile is "Basic Technical Objects" (BTO). There are a small set of technical objects that are used in DDI to support identification, referencing, dates, external controlled vocabularies, string content, and the basic features of ISO/IEC 11179-5 (Name, Label, Description). This profile provides guidance for the best practice usage of these technical objects to support interoperability. In particular it identifies those objects which should be considered interoperable and applied in a consistent manner, and those that contain primarily local information.
- Variable Profile: This profile covers those DDI objects required to support the Variable, Population and Concept objects in GSIM.
- Represented Variable Profile: This profile covers those DDI objects required to support the Represented Variable, Enumerated Value Domain, Described Value Domain and Unit of Measure objects in GSIM.
- Questionnaire Profile: This is the definition of a 3.2 DDI profile for business questionnaire - test version. This profile includes all the objects, schemes and 'packaging' information needed to create a complete questionnaire, including Questions, Question Groups and Blocks, Statements, Interviewer Instructions, Controls and Instrument.
- Codelist Profile: This profile covers those DDI objects required to support Code Lists and Category Sets in GSIM.