Subject: RE: AttributeTypeValue and binary

From: "Ramsay, Ron" <[email-masked]>
Date: Thu, 25 Jan 2001 14:09:05 +1100

Kurt,

Let us return to the beginning.

In the beginning, all syntaxes were specified in ASN.1 by reference to
X.500. LDAP tried to give these a friendly face by defining human-readable
encodings, the so-called 'string' encodings. I believe that 'string' in LDAP
means human-readable.

I don't see how string-encoding can encompass binary syntaxes. If ASN.1
syntaxes are string encodings then what could a document called 'A string
encoding for dustinguished names' actually be trying to do - all
distinguished names carried in protocol (DAP, here!) would be string
encodings by virtue of being BER encoded.

The reference to RFC 2251, 4.1.6 seems to be tautological: it says that RFC
2251 does not define string encodings for attributes.

But you are correct when you say that binary and string encodings are
carried in the same way in the protocol. This is syntactically correct but
not semantically correct in that many atrtributes have an ASN.1
representation but only the string representation can normally be used.

Ron.

PS RFC 2251 does not define 'string encoding' though it uses the term
(loosely) in 4.1.6. It does define binary encoding (4.1.5.1).

-----Original Message-----
From: Kurt D. Zeilenga [mailto:[email-masked]]
Sent: Thursday, 25 January 2001 12:55
To: Ramsay, Ron
Cc: Mark Smith; Jim Sermersheim; [email-masked]
Subject: RE: AttributeTypeValue and binary

At 12:21 PM 1/25/01 +1100, Ramsay, Ron wrote:
>I am surprised that you refer to the binary syntax as having a defined
>string encoding. This seems to imply new meanings for both 'defined' and
>'string' and a possibly ambiguous use of 'encoding'.

RFC 2251, 4.1.6:
   The definition of string encodings for different syntaxes and types
   may be found in other documents, and in particular [5].

I am using "string encoding" as used in RFC 2251.  I note
that there is no need to mention the binary syntax within
RFC 2251 as its transfer within the protocol is no different
from any other attribute type syntax which has a defined
string encoding.  I qualify with "defined" as some syntaxes,
such as ACI Item, have no specified string encoding.

---

From: "Kurt D. Zeilenga" <[email-masked]>
Date: Wed, 24 Jan 2001 19:49:47 -0800

>encodings, the so-called 'string' encodings. I believe that 'string' in LDAP

No.  JPEG has a 'string' encoding but is not human-readable.
("Values in this syntax are encoded as strings...")

>I don't see how string-encoding can encompass binary syntaxes.

Because values of this syntax are encoded as strings contain
BER encoded instances of an ASN.1 data type.