When an element is created in Design it gains a unique internal reference number of the form "=<integer>/<integer>", e.g. =13/2305. On export from Design this value, excluding the initial '=' character, will be passed through in Packet 10 or 20 in the Mark fields. These are text strings on Records 3 and 3a respectively. Any system importing this file should be able to take this value and store it, or use it to allow the user of the detailing system to identify the Design member in the external steel detailing package. On Export back to AVEVA E3D™, for any member which has this Mark attribute set, the original imported Mark value will appear again in the SDNF file. Thus a user of Design will be able to spot any changes to the model. The AVEVA SDNF Import system, then allows the user to modify the existing structure, rather than just replacing it with a copy. In this way, any drawings for example, which may have been produced between Export from and Import back to Design, will retain their logical relationships to the steel members.

A member created outside Design will not have the Mark field set to be an AVEVA E3D™ internal reference number. The AVEVA SDNF interface would therefore know that it was importing a new element and would create it accordingly, whilst recording the external Mark number as well.