Path: utzoo!attcan!uunet!cos!grieve
From: grieve@cos.com (David Grieve)
Newsgroups: comp.protocols.iso
Subject: Re: FTAM, Contents-type attribute
Keywords: FTAM, Contents-type, parameters
Message-ID: <40288@cos.com>
Date: 9 Nov 90 14:13:00 GMT
References: <1006@sl10c.concurrent.co.uk>
Reply-To: grieve@cos.UUCP (David Grieve)
Organization: Corporation for Open Systems, McLean, VA
Lines: 46

In article <1006@sl10c.concurrent.co.uk> Alan Young <awy@concurrent.co.uk> writes:
]I have a problem with interpretation FTAM Part 2 (ISO 8571-2 or BS
]7090:Part 2:1989) concerning section 12.3 "Contents Type" and the use of
]the Contents-type attribute on an F-OPEN request (ISO 8751-3 section
]17.1.2.4). 
]..
](paragraphs c, d and e of section 12.3).
]
]    c) a document type name without parameters, in which case the match
]    must be exact;
]
]    d) a document type name with null parameters, in which case the name
]    must match, but the parameter values are supplied from the attribute
]    value;
]
]    e) a document type name with non-null parameters, in which case the
]    name must match, and the parameters must match or be a relaxation.
]
]For case (c) above, when the document type name matches that of the file
]attribute value, should the parameters be taken to be those of the file
]attribute value, as is explicitly stated in case (d)?  I am at a loss to
]see any other interpretation. 

Yes. 17.1.2.4 states that if the open regime is successful, then the
response conveys the contents type file attribute. In otherwords,
the attributes with which the file was created are returned. 
    
]For case (d) what are "null" parameters?  Presumably for the
]FTAM-1 example a SEQUENCE with all the optional elements (all the
]elements in this case) omitted.  How is this different from the
]case (which would be covered by paragraph (e)) where the real
]parameters of the file attribute value are significantly omitted? 

I believe the difference is that null parameters (case d) would be the
parameter field encoded with a length of zero. Using your example -
{FTAM-1, {,,}} - the parameter field would have a length of 6 (1
identifier octet plus one length octet for each parameter -- no contents  
octet since the parameter is null).  Case d would be encoded {FTAM-1, {}} 
so that the length of the parameter field would be zero.  This is _my_ 
understanding of the difference. 

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