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.
- What is DDI?
- What is XML?
- What are the benefits of using the DDI?
- How can I get started using the DDI?
- What is the DDI Alliance? How can I participate?
- 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?
- I have used DDI Codebook Version 2 for markup at my organization. Do I need to migrate to DDI Lifecycle Version 3 or above?
- Why is the Alliance creating DDI 4 when DDI Codebook and DDI Lifecycle are available?
- Does a new version of DDI mean older versions will no longer be supported?
- When will DDI 4 be ready for production?
- What kind of comments about the DDI 4 Prototype are being solicited?
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:
W3C (World Wide Web Consortium):
Robin Cover: http://www.oasis-open.org/cover/
Great collection of links to all things SGML/XML.
Interesting articles on XML: http://www.xml.com/
Benefits of the DDI approach are discussed in the Why Use DDI section of this site.
If you're interesting in using the DDI, you should look at the section of this site on Getting Started with DDI.
Information on the organization itself can be found in the DDI Alliance section of this Web site.
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.
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.
DDI has continuously evolved to meet the needs of its user community. The goals of DDI 4 to produce a model-based specification that can be more easily managed, extended, and expressed in different representations such as RDF, JSON, and database schemes. Another goal of a new version of DDI is the ability to auto-generate DDI instead of creating “by hand.”
No! The Alliance continues to support, develop, and encourage the adoption of DDI-Codebook (DDI 2) and DDI-LIfecycle (DDI 3). The DDI 4 Prototype release is intended for public review and feedback on the model-based approach to developing a DDI specification.
The next steps in developing DDI 4 will be determined by amount and degree of feedback about the Prototype. The DDI Alliance encourages individuals and organizations interested in participating in DDI 4 development to get involved. The Alliance encourages users and potential users to try DDI’s two production-ready version: DDI Codebook (2.x) or DDI Lifecycle (3.x).
The DDI Alliance is soliciting such feedback as:
- Does this Prototype provide functionality that you or your organization find useful?
- If not, what do you see as barriers to implementing DDI 4?
- Would your organization use the XML or RDF bindings?
- How would you or your organization actually use and/or implement DDI 4?