A basic design goal of SGML was to ensure that documents encoded according to its provisions should be transportable from one hardware and software environment to another without loss of information. The structure of SGML is based on a grouping of sections and elements that are annotated by start and end tags. Tags are user-friendly phrases used to indicate the data elements contained within the tags. For example:
In this example, the starting and ending tags "patient birthdate" indicate that the data within the tags is the patient's birthdate. The relationship and order of data elements is further defined by document type definition (DTD). DTDs are document-specific specifications for the structure of an SGML document. In the following example, the DTD has specified that the order of the information be presented as:
Using the above example the data must be presented in the following order to be in conformance with the DTD:
Patient birth date
Patient onset age
Patient onset age unit
If the data elements are presented in any other order (e.g., patient onset age, patient onset age unit, patient birth date) the elements are not in conformance with the SGML DTD for the document.
For electronic submission of adverse event data, a specific SGML DTD has been specified by the ICH. The ICH ICSR DTD defines the specific data elements to be included for electronic submission of adverse event data, the order of the elements, and their interrelationship.
