All textual data (including some data that is rendered in a textual form) is Unicode. A common text length, used for most names and representations, is 255 characters. Descriptions take 2000 characters. Actually, the maximum length of text is one less, due to the terminating 0-character that the ITP/MDK Repository stores.
Objects (entries) in the ITP/MDK Repository DID are identified with a unique reference, mostly called a "Ref" in the DID source. This is a Unicode text string of 50 characters. It is an internal identification, not intended to be shown in a result document. Every entry refers to itself with a 'Self' field, which contains such a reference. It may refer to other entries by reference fields (whose name commonly ends in "…Ref"), but these are for internal use: related objects are given by subentries.
Most entries, except the revision objects, have a Name field.
"Boolean" fields and return values are represented by a number: 1 is 'TRUE' and 0 is 'FALSE'.
With the exception of Characteristic and CharacteristicGroup, most objects have a Boolean (0 or 1) 'Limbo' field that indicates that the object has been marked for deletion.