Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!ucsd!helios.ee.lbl.gov!ncis.tis.llnl.gov!eng.sun.COM!pv From: pv@eng.sun.COM (Peter Vanderbilt) Newsgroups: comp.protocols.iso.x400 Subject: questions about 88 X.400 Message-ID: <8912012309.AA02246@polya.Eng.Sun.COM> Date: 1 Dec 89 23:09:43 GMT Sender: root@ncis.tis.llnl.gov Distribution: inet Organization: The Internet Lines: 55 Approved: post-x400@tis.llnl.gov I have some questions on 1988 X.400 externally defined body parts. (Note: ExternallyDefinedBodyPart ::= SEQUENCE { parameters ExternallyDefinedParameters, data ExternallyDefinedData} ExternallyDefinedParameters ::= EXTERNAL ExternallyDefinedData ::= EXTERNAL ). First, what is the relation between the object identifiers (OIDs) for the data, parameters and EITs (encoded information types) for each body part type? May they be the same? (In general, does context play a role in the mapping from OIDs in EXTERNALs to abstract syntaxes? I.e. can the same OID be used in different EXTERNALs?) In the case where a set of EIT OIDs is defined for a given type (to encode non basic parameters), is there any guaranteed commonality? For example, will they all be under a specific subtree? Why does the standard say, in section 7.3.12 (note 2), "If an Externally Defined body part has a Parameters component, ..." when the parameters component is not optional? (Note that an extended body part type with no PARAMETERS clause implies NULL as the parameters' type). Why wasn't it made optional? Second, for the built-in types what are the OIDs used in the "parameters" EXTERNALs? For example, X.400 defines that the OID for IA5 text data is id-et-ia5-text ({2 6 1 4 0}) and that the EIT is given by either built-in ia5-text(2) or the external OID id-eit-ia5-text ({2 6 3 4 2}). But what is the OID for the parameters? (For EITs, which is favored, the built-in value or the external one?) Third, are there any restrictions on the encoding CHOICE for the EXTERNALs (other than those implied by ASN.1)? (Note for X.400 the EXTERNAL can be simplied to: EXTERNAL ::= [Universal 8] IMPLICIT SEQUENCE { direct-reference OBJECT IDENTIFIER OPTIONAL, encoding CHOICE { single-ASN1-type [0] ANY, octet-aligned [1] IMPLICIT OCTET STRING, arbitrary [2] IMPLICIT BIT STRING } } ). Presentation has a similar construction with rules to the effect that if the single-ASN1-type can be used, it must be. Is there a similar rule for EXTERNALs? If not, is the choice up to the sender or to the definer of the body part type? Pete Brought to you by Super Global Mega Corp .com