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Re: Definition of 'Body Part' in MIME draft, part 1

1995-04-18 00:27:11
Thank you for your reply. Unfortunately, it does not satisfy me, so I feel
I must go on, sorry.

As for the definition of an entity, this term originated in RFC1521 and
is defined in the next section in both RFC1521 and the current draft.

I know those definitions very well. They were indeed in RFC1521, and they
were already in RFC1341. At some time during the preparation of what
would become RFC1341, the terminology used was quite unclear, so I did
write and propose the four definitions (message, body part, entity and
body) to the working group, who accepted them. I then made a pass on the
document to straighten the terminology, and submitted the corrections to
Nathaniel who applied them to the text. So, please consider that I really
have a full understanding of those definitions and their implications, since
I wrote them in the first place. So I feel entitled to ask you to read this
message carefully.

The definition of 'body part' was introduced to have a term to designate
one part of a multipart body without confusion. There are places were one
must speak about either a message or a body part: that's why the definition
of 'entity' has been introduced. An entity is either a message or a body part.
Then, the definition of body makes reference to 'entity', so the term 'body',
without 'part', is used to designate the body of either a message or of a
body part. Those definitions were thus designed to have one word to designate
each kind of object without uncertainty. BTW, that's the purpose of definitions
in any discipline, and changing a definition after it has been used as a base
for development for five years is risky.

Read the definition again. It says a body part can be a *part*
of a multipart entity. Nowhere does it say its an entity.

The 'new' definition says that a body part is 'either a single part message or
one of the parts...'. That means that it can now also be a message. One thing
wrong with this, is that the text speaks of what makes sense in the header
of a body part (only Content-xxx lines make sense), while in a message all
the header lines defined in RFC822 and successors do make sense.

This is also incorrect. The old definition specified that a "body part" was
always a piece of a large multipart structure. And this is wrong, plain and
simple, since MIME messages can and often do consist of a single "body part"
that is *not* enclosed inside of a multipart entity.

Of course, the body of many messages is of a 'discrete' type. This does not
make such messages 'body parts'. What are they ? Messages, of course. Which
means that they have a (message) header and a body. They may also be called
an entity, and everything that is written about entities applies to them.
But they cannot be called body parts. Look at their header, for example.
You will find a 'From:' line, which is mandatory in messages, but does not
make sense in body part, etc. There is really no reason to change the
definition of body part, which was designed to speak about one part of
a multipart, to now also designate some kind of message. Nothing is gained,
since a message can be called 'message' (or entity if the properties common
to messages and body parts are to be applied). And there is no place in
the specification were things must be said about messages with a discrete
type body that does not apply to a general message (that's one of the beauties
of MIME, that it is completely recursive, and that each occurence of a
'message' may be again a multipart). Much is lost, since with the
'new' definition one does not have any word anymore to designate a part
of a multipart body when properties unique to those body part must be

And every use of the term
"body part" corresponds to the new definition, not the old one, so

Really, no. I did read the documents once again, and each and any occurence
of 'body part' is there to speak about properties unique to the parts of
a multipart body. What is true (of course), is that the term 'body' (without
the 'part' qualifier) is used to speak about the body of either a message
or a body part. But that's what is has been designed for per the fourth

the new definition is going to stay.

I urge you to reconsider this. If the explanations in this message are not
clear/convincing enough, I will produce examples from the texts to show
what I mean in a more illustrated way. Thank you for your kind attention.


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