FAQ

What is DDI?

The DDI is a metadata specification for describing social and behavioral science data and data in related domains. Essentially, the DDI is a way of formatting the documentation for a social science data file, such that it is much more useful than a simple MS Word or text file. The tagged structure enables computer processing of the information.

DDI is used to document datasets and allow search in many social science data archives around the world. Examples of the use of DDI can be found on the DDI Adopters page.

The DDI is currently a specification, not a standard. While the DDI has not yet become a formal ISO standard, that is an important goal of the initiative.

  1. What is DDI?
  2. What is XML?
  3. What are the benefits of using the DDI?
  4. How can I get started using the DDI?
  5. What is the DDI Alliance? How can I participate?
  6. I am starting a new project. How do I know whether I should use DDI Codebook or DDI Lifecycle as the basis for my markup?
  7. I have used DDI Codebook Version 2 for markup at my organization. Do I need to migrate to DDI Lifecycle Version 3 or above?
  8. Why is the Alliance creating DDI - Cross Domain Integration (DDI-CDI) when DDI Codebook and DDI Lifecycle are available?
  9. Does a new version of DDI mean older versions will no longer be supported?
  10. When will DDI-CDI be ready for production?
  11. What kind of comments about the DDI-CDI Public Release are being solicited?
  12. What is XML?

    XML stands for Extensible Markup Language and is a way of tagging text for meaning, instead of appearance.

    If you wanted to emphasize the name of a variable in a codebook, you'd probably make it bold or type it in all capitals, but you would also use that same emphasis for the study title, or for important notes on using the data. To easily identify variable names, which would make your documentation much more useful, you need more than formatting and display options. In XML, you surround your information with tags that have meaning and differentiate information:

    <study-title>Euro-barometer</study-title>
    
    <summary>This study was conducted in <time-period>April 1994</time-period>
    and covered....</summary>
    

    With a good search engine, it would thus be possible to search for studies done in April 1994, and this study would be returned as a result.

    To learn more about XML, see:
     

  13. What are the benefits of using the DDI?

    Benefits of the DDI approach are discussed in the Why Use DDI section of this site.

  14. How can I get started using the DDI?

    If you're interesting in using the DDI, you should look at the section of this site on Getting Started with DDI.

  15. What is the DDI Alliance? How can I participate?

    Information on the organization itself can be found in the DDI Alliance section of this Web site.

  16. I am starting a new project. How do I know whether I should use DDI Codebook or DDI Lifecycle as the basis for my markup?

    DDI Version 3 has a number of new features that were introduced to answer specific user needs:

    -It makes it possible, and convenient, to describe groups of studies that are related along one or several dimensions (time, geography, etc.). It also provides for documenting comparable items (concepts, questions, variables) among members of a group. This feature is particularly useful in marking up time-series, or multi-national studies, as well as documenting harmonized data.

    -It provides more complete documentation for complex data files (i.e., hierarchical data, with related records).

    -It also includes a new section designed for marking up questionnaires, with instrument characteristics, question text, conditions, and question flow (skip patterns). Questions can be linked to variables, but they are no longer "children" of a variable, as they were in Versions 1/2.

    -It enables documenting aggregate data both in a (comma) delimited format and a spreadsheet-type format, where locations are expressed as column/row.

    -It also provides for marking up and transporting the actual data - either aggregate, or microdata - in an XML format.

    -It offers significantly enhanced documentation for geographic coverage, with a description of all levels of geography that includes a mandatory specification of the highest and lowest levels, links to the geographic variables, etc.

    -It provides better documentation for translations, including coverage of multi-lingual studies.

    If you need to use any of the above-mentioned features in your DDI project(s), then the obvious answer would be to start using Version 3. If, on the other hand, you are only working with simple, microdata, survey-type studies, or if you are only producing study descriptions (catalog records), Versions 1/2 may be used, particularly if they appear to answer all your current and foreseeable needs.

  17. I have used DDI Codebook Version 2 for markup at my organization. Do I need to migrate to DDI Lifecycle Version 3 or above?

    See the answer above. If you do decide to migrate to DDI Lifecycle, you may want to make use of the Correspondence Mapping between Codebook 2.1 and Lifecycle 3.0.

  18. Why is the Alliance creating DDI - Cross Domain Integration (DDI-CDI) when DDI Codebook and DDI Lifecycle are available?

    DDI has continuously evolved to meet the needs of its user community. The goals of DDI-Cross Domain Integration (DDI-CDI) is not to replace earlier versions of DDI, but to provide a complementary tool which allows data described in DDI to be more easily integrated with data from non-traditional sources which have become common.  DDI-CDI is not designed to be a data management tool in the way that DDI Codebook and DDI Lifecycle are: DDI-CDI details the roles played by atomic datums and how they function and can be expressed in different formats (as long data sets or streams, in "big" data/no SQL environments, etc.).  Once integrated, data will still be managed using the metadata set found in earlier versions of DDI, which is not the focus of DDI-CDI.

  19. Does a new version of DDI mean older versions will no longer be supported?

    No! The Alliance continues to support, develop, and encourage the adoption of DDI-Codebook (DDI 2) and DDI-LIfecycle (DDI 3). The DDI-CDI release is an application of the DDI 4 model to provide new functionality, not to replace existing systems based on DDI.

  20. When will DDI-CDI be ready for production?

    The next steps in developing DDI-CDI will be determined by the amount and degree of feedback during the Public Review. It is expected that after the initial Public Review cycle, there will be another release for testing and approval, reflecting comments made during the initial Public Review.  This process will require several months to complete.  The DDI Alliance encourages individuals and organizations interested in participating in DDI-CDI development to get involved. 

  21. What kind of comments about the DDI-CDI Public Release are being solicited?

    The DDI Alliance is soliciting such feedback as:

    • Does this specification provide functionality that you or your organization find useful?
    • If not, what do you see as barriers to implementing DDI-CDI?  What else should it support?
    • What technology platform would your organization use to implement the DDI-CDI model?  XML?  RDF?  Other programming platforms?
    • How would you or your organization actually use and/or implement DDI-CDI?