All DDI codebooks must have a study description which contains information
about the study overall. The Study Description consists of information about the data
collection, study, or compilation that the DDI-compliant documentation file
describes. This section includes information about how the study should be
cited, who collected or compiled the data, who distributes the data,
keywords about the content of the data, summary (abstract) of the content
of the data, data collection methods and processing, etc. At least
one citation must be present, capturing the whole study. More information
on this element, especially the allowed attributes, can be found in the references.