Network Working Group S. Hollenbeck
Internet-Draft VeriSign, Inc.
Expires: October 4, 2002 M. Rose
Dover Beach Consulting, Inc.
L. Masinter
Adobe Systems Incorporated
April 5, 2002
Guidelines For The Use of XML in IETF Protocols
draft-hollenbeck-ietf-xml-guidelines-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on October 4, 2002.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
The eXtensible Markup Language (XML) is a framework for structuring
data. While it evolved from SGML -- a markup language primarily
focused on structuring documents -- XML has evolved to be a widely-
used mechanism for representing structured data.
There are a wide variety of Internet protocols; many have need for a
representation for structured data relevant to their application.
There has been much interest in the use of XML as a representation
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method. This document describes basic XML concepts, analyzes various
alternatives in the use of XML, and provides guidelines for the use
of XML within IETF standards-track protocols.
Intended Publication Status
It is the goal of the authors that this draft (when completed and
then approved by the IESG) be published as a Best Current Practice
(BCP).
Conventions Used In This Document
This document recommends, as policy, what specifications for Internet
protocols -- and, in particular, IETF standards track protocol
documents -- should include as normative language within them. The
keywords "SHOULD", "MUST", "MAY", etc. are used in the sense of how
they would be used within other documents with the meanings as
specified in RFC 2119 [1].
Discussion Venue
The authors welcome discussion and comments relating to the topics
presented in this document. Though direct comments to the authors
are welcome, public discussion is taking place on the "ietf-xml-use"
mailing list. To join the list, send a message to "ietf-xml-use-
request@imc.org" with the word "subscribe" in the body of the
message. There is a web site for the list archives at http://
www.imc.org/ietf-xml-use/.
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Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 4
1.1 Intended Audience . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 XML Evolution . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 XML Users, Support Groups, and Additional Information . . . . 5
2. XML Selection Considerations . . . . . . . . . . . . . . . . . 6
3. XML Alternatives . . . . . . . . . . . . . . . . . . . . . . . 7
4. XML Use Considerations and Recommendations . . . . . . . . . . 9
4.1 XML Declarations . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 XML Processing Instructions . . . . . . . . . . . . . . . . . 9
4.3 Well-Formedness . . . . . . . . . . . . . . . . . . . . . . . 10
4.4 Validity . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.5 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.6 Element and Attribute Design Considerations . . . . . . . . . 11
4.7 Binary Data . . . . . . . . . . . . . . . . . . . . . . . . . 11
5. Internationalization Considerations . . . . . . . . . . . . . 13
5.1 Character Sets . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2 Language Declaration . . . . . . . . . . . . . . . . . . . . . 13
5.3 Other Considerations . . . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
Normative References . . . . . . . . . . . . . . . . . . . . . 18
Informative References . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 21
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 22
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1. Introduction and Overview
The eXtensible Markup Language (XML) is a framework for structuring
data. While it evolved from the Standard Generalized Markup Language
(SGML) [18] -- a markup language primarily focused on structuring
documents -- XML has evolved to be a widely-used mechanism for
representing structured data in protocol exchanges. See [34] for an
introduction to XML.
1.1 Intended Audience
Many Internet protocol designers are considering using XML and XML
fragments within the context of existing and new Internet protocols.
This document is intended as a guide to XML usage and as IETF policy
for standards track documents. Experienced XML practitioners will
likely already be familiar with the background material here, but the
guidelines are intended to be appropriate for those readers as well.
1.2 Scope
This document is intended to give guidelines for the use of XML
content within a larger protocol.
There are a number of protocol frameworks already in use or under
development which focus entirely on "XML protocol": the exclusive use
of XML as the data representation in the protocol. For example, the
World Wide Web Consortium (W3C) is developing an XML Protocol
framework [31] based on the Simple Object Access Protocol (SOAP)
[35]. The applicability of those protocols is not part of the scope
of this document.
In addition, there are higher-level representation frameworks, based
on XML, that have been designed as carriers of certain classes of
information; for example, the Resource Description Framework (RDF)
[30] is an XML-based representation for logical assertions. This
document does not provide guidelines for the use of such frameworks.
1.3 XML Evolution
Originally published in February 1998 [29], XML's popularity has led
to several additions to the base specification. Although these
additions are designed to be consistent with version 1.0 of XML, they
have varying levels of stability, consensus, and implementation.
Accordingly, this document identifies the major evolutionary features
of XML and makes suggestions as to the circumstances in which each
feature should be used.
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1.4 XML Users, Support Groups, and Additional Information
There are many XML support groups, some devoted to the entire XML
industry (e.g., http://xml.org/), some devoted to developers (http://
xmlhack.com/), some devoted to the business applications of XML
(e.g., http://oasis-open.org/), and many, many groups devoted to the
use of XML in a particular context.
It is beyond the scope of this document to provide a comprehensive
list of referrals. Interested readers are directed to the three
links above as starting points, as well as their favorite Internet
search engine.
(TBD: pointers to other best practice and design guidelines, such as
http://www.xfront.com/BestPracticesHomepage.html and http://
www.goland.org/xmlschema.htm)
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2. XML Selection Considerations
XML is a tool that provides a means towards an end. Choosing the
right tool for a given task is an essential part of ensuring that the
task can be completed in a satisfactory manner. This section
describes factors to be aware of when considering XML as a tool for
use in IETF protocols:
o XML is a meta-markup language that can be used to define markup
languages for specific domains and problem spaces.
o XML provides both logical structure and physical structure to
describe data. Data framing is built-in.
o XML includes features to support internationalization and
localization.
o XML is extensible. New tags (and thus new protocol elements) can
be defined without requiring changes to XML itself.
o XML is still evolving. The formal specifications are still being
influenced and updated as use experience is gained and applied.
o XML is text-based, so XML fragments are easily created, edited,
and managed using common utilities. Further, being text-based
means it more readily supports incremental development, debugging,
and logging.
o XML is verbose when compared with many other data encapsulation
languages. A representation with element extensibility and human
readability typically requires more bits when compared to one
optimized for efficient machine processing.
o XML implementations are still relatively new. As designers and
implementers gain experience, it is not uncommon to find defects
in early and current products.
o XML support is available in a large number of software development
utilities, available in both open source and proprietary products.
o XML processing speed can be an issue in some environments. XML
processing can be slower because XML data streams may be larger
than other representations, and the use of general purpose XML
parsers will add a software layer with its own performance costs.
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3. XML Alternatives
This document focuses on guidelines for the use of XML, but it's
useful to consider why one would use XML as opposed to some other
mechanism. This section considers some other commonly used
representation mechanisms and compares XML to those alternatives.
For example, Abstract Syntax Notation 1 (ASN.1) [16] along with the
corresponding Basic Encoding Rules (BER) [17] are part of the OSI
communication protocol suite, and have been used in many subsequent
communications standards (e.g., the ANSI Information Retrieval
protocol [15] and the Simple Network Management Protocol (SNMP)
[21]). The eXternal Data Representation (XDR) [22] and variations of
it have been used in many other distributed network applications
(e.g., the Network File System protocol [28]). With ASN.1, data
types are explicit in the representation, while with XDR, the data
types of components are described externally as part of an interface
specification.
Many other protocols use data structures directly (without data
encapsulation) by describing the data structure with Backus Normal
Form (BNF) [13]; many IETF protocols use an Augmented Backus-Naur
Form (ABNF) [24]. The Simple Mail Transfer Protocol [27] is an
example of a protocol specified using ABNF.
Representation methods differ from XML in several important ways:
Specification encoding: XML schema are themselves represented in XML,
and the specification itself can be written using arbitrary
characters from the language. The specification of representations
in other systems (ASN.1, XDR, ABNF) are generally in ASCII [14] text.
Text Encoding and character sets: the character encoding used to
represent a formal specification. XML defines a consistent character
model based on ISO 10646 [19], with a base that supports at least
UTF-8 [4] and UTF-16 [26], and allows for other encodings. While
ASN.1 and XDR may carry strings in any encoding, there is no common
mechanism for defining character encodings within them. Typically,
ABNF definitions tend to be defined in terms of octets or characters
in ASCII.
Data Encoding: XML is based on a character model. XML Schema [11]
includes mechanisms for representing some datatypes (integer, date,
array, etc.) but other binary datatypes are encoded in Base64 [23].
ASN.1 and XDR have rich mechanisms for encoding a wide variety of
datatypes.
Extensibility: XML has a rich extensibility model: XML
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representations can frequently be versioned independently. Many XML
representations can be extended by adding tokens to the XML namespace
(if done compatibly); other extensions can be added by adding to the
namespace. ASN.1 is similarly extensible through the use of Object
Identifiers (OIDs). XDR representations tend to not be independently
extensible by different parties because the framing and datatypes are
implicit and not self-describing. The extensibility of BNF-based
protocol elements needs to be explicitly planned.
Legibility of protocol elements: As noted above, XML is text-based,
and thus carries the advantages (and disadvantages) of text-based
protocol elements. Typically this is shared with (A)BNF-defined
protocol elements. ASN.1 and XDR use binary encodings which are not
visible.
ASN.1, XDR, and BNF are described here as examples of alternatives to
XML for use in IETF protocols. There are other alternatives, but a
complete enumeration of all possible alternatives is beyond the scope
of this document.
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4. XML Use Considerations and Recommendations
This section notes several aspects of XML and makes recommendations
for use. Since the 1998 publication of XML version 1 [29], an
editorial second edition [8] was published in 2000; this section
refers to the second edition.
4.1 XML Declarations
An XML declaration (defined in section 2.8 of [8]) is a small header
at the beginning of an XML data stream that indicates the XML version
and the character encoding used. For example,
<?xml version="1.0" encoding="UTF-8"?>
specifies the use of XML version 1 and UTF-8 character encoding.
Protocol specifications must be clear about use of XML declarations.
In some cases, the XML used is a small fragment in a larger context,
where the XML version and character encoding are specified
externally. In those cases, the XML declaration might add extra
overhead. In other cases, the XML is a larger component which may
find its way alone as an external entity body, transported as a MIME
message. In those cases, the XML declaration is an important marker
and useful for reliability and extensibility. In general, an XML
protocol element should either disallow XML declarations ("MUST NOT
be used") or require one ("MUST have"). A design which allows but
does not require an XML declaration leads to unreliable
implementations. When in doubt, require an XML declaration.
4.2 XML Processing Instructions
An XML processing instruction (defined in section 2.6 of [8]) is a
component of an XML document that signals extra "out of band"
information to the receiver; a common use of XML processing
instructions are for document applications. For example, the XML2RFC
application used to generate this document and described in [25]
supports a "table of contents" processing instruction:
<?rfc toc="yes"?>
Again, protocol specifications must be clear about whether -- and if
so, what kind of -- XML processing instructions are allowed.
However, XML processing instructions appear to have rare
applicability to XML fragments embedded in Internet protocols, and it
is recommended that their use be explicitly disallowed ("MUST NOT
use"). In cases where XML processing instructions are allowed, the
nature of the allowable processing instructions should be specified
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explicitly.
4.3 Well-Formedness
A well-formed XML instance is one in which all character and markup
data conforms to a specific set of structural rules defined in
section 2.1 of [8].
An XML instance that is not well-formed is not really XML; well-
formedness is the basis for syntactic compatibility with XML.
Without well-formedness, most of the advantages of using XML
disappear. For this reason, it is imperative that protocol
specifications REQUIRE that XML instances be well-formed.
4.4 Validity
Beyond well-formedness there are additional mechanisms that define a
set of structural and data format constraints. Two mechanisms are
commonly used to define grammars for classes of XML documents:
Document Type Definition (DTD) (defined in section 2.8 of [8]) and
XML Schema (defined in [10] and [11]).
DTDs are an older technology that has been found to have drawbacks,
particularly in the features provided for extensibility and data
typing. XML Schema was designed to address many DTD shortcomings.
For example, with a DTD a validating parser can confirm that an
element contains character data, but with XML Schema a validating
parser can also confirm that the value of an element matches a
particular regular expression.
XML Schema provides powerful features to define a complete and
precise specification of allowable protocol syntax and data type
definitions. In order to obtain the advantages of XML as a data
structure specification system, protocol specifications should supply
an XML Schema and insist that XML instances MUST be valid according
to that schema.
4.5 Namespaces
XML namespaces, defined in [9], provide a means of assigning markup
to a specific vocabulary. If two elements or attributes from
different vocabularies have the same name, they can be distinguished
unambiguously if they belong to different namespaces. Additionally,
namespaces provide significant support for protocol extensibility as
they can be defined, reused, and processed dynamically.
Markup vocabulary collisions are very possible when namespaces are
not used to separate and uniquely identify vocabularies. Protocol
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definitions should use existing XML namespaces where appropriate.
When new namespaces are needed, the namespace name (a URI) should be
defined within the RFC itself, and the IETF URN namespace described
in [20] should be used to designate the namespace; for example:
abc:xmlns="urn:ietf:params:xml:ns:abc"
4.6 Element and Attribute Design Considerations
XML provides much flexibility in allowing a designer to use either
elements or element attributes to carry data. Element attributes are
generally intended to contain meta-data that describes the value of
the element, and as such they are subject to the following
restrictions:
o Attributes are unordered, and
o Attribute values can only contain simple XML data types.
Consider the following example that describes an IP address using a
"type" attribute to describe the address value:
<address type="ipv4">10.1.2.3</address>
XML allows the same information to be encapsulated using a <type>
element instead of a "type" attribute:
<address>
<type>ipv4</type>
<value>10.1.2.3</value>
</address>
The preferred form is used in the first example, where the "type"
attribute is used to describe the value of the <address> element.
Consistent use of elements and element attributes is a characteristic
of a sound design. Protocols are strongly urged to use elements as
the primary XML data encapsulation structure. Attributes used in
protocol elements should contain only meta-data that describes the
value of the enclosing element.
4.7 Binary Data
XML is defined as a character stream rather than a stream of octets,
and such there are no ways of embedding binary data directly within
an XML data stream. XML Schema [11] defines one encoding of binary
data using Base64 [23] and another using hexadecimal digits.
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Other protocols transmit binary data using some other communication
channel, and include, in the XML data itself, a reference (using the
anyURI data type).
Protocols that need a container that can hold both structural data
and large quantities of binary data should consider carefully whether
XML is appropriate, since the Base64 and hex encodings are
inefficient. Otherwise, protocols should use the mechanisms of XML
Schema to represent binary data; the Base64 encoding is best for
larger quantities of data, while the hex encoding will work for short
bit strings.
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5. Internationalization Considerations
This section describes internationalization considerations for the
use of XML to represent data in IETF protocols. Readers should be
familiar with IETF policy on the use of character sets and languages
as described in RFC 2277 [3].
5.1 Character Sets
XML provides native support for encoding information using the
Unicode character set and its more compact representations including
UTF-8 [4] and UTF-16 [26]. Other encodings are also supported and
can be specified using an "encoding" attribute in a document's XML
declaration. It is strongly recommended that UTF-8 be mandated for
protocols that represent data using XML.
Guidelines for the use of XML declarations can be found in Section
4.1. If an XML declaration is omitted, it is strongly urged to
require use of a consistent character set, and to require UTF-8 as
the most appropriate character set. If an XML declaration is
allowed, it is again strongly urged to require use of a consistent
character set, to require UTF-8 as the most appropriate character
set, and to recommend inclusion of an "encoding" attribute that
explicitly notes use of UTF-8 encoding.
5.2 Language Declaration
Text encapsulated in XML can be represented in many different human
languages, and it is often useful to explicitly identify the language
used to present the text. XML version 1 defines a special attribute
in the "xml" namespace, xml:lang, that can be used to specify the
language used to represent data in an XML document. The xml:lang
attribute and the values it can assume are defined in section 2.12 of
[8].
It is strongly recommended that protocols representing data in a
human language mandate use of an xml:lang attribute if the XML
instance might be interpreted in language-dependent contexts.
5.3 Other Considerations
There are standard mechanisms in the typography of some human
languages that can be difficult to represent using merely XML
character string data types. For example, pronunciation clues can be
provided using Ruby annotation [32], and embedding controls (such as
those described in section 3.4 of [36]) or an XHTML [33] "dir"
attribute can be used to note the proper display direction for
bidirectional text.
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It is strongly recommended that protocols representing data in a
human language reuse existing mechanisms as needed to ensure proper
display of human-legible text.
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6. IANA Considerations
This section does not contain any specific directives for IANA.
However, when XML is used in an IETF protocol there are multiple
factors that might require IANA action, including:
o XML media types. Some protocols have protocol elements that are
MIME bodies, and allow MIME labeling. In cases where a MIME label
is used to identify a protocol element the MIME labeling policies
defined in RFC 3023 [5] should be followed and an XML declaration
should be present. The "application/xml" media type is most
appropriate for general XML; if a new media type is expected, it
should be registered.
o URI registration. There is an ongoing effort [20] to create a URN
namespace explicitly for defining URIs for namespace names and
other URI-designated protocol elements for use within IETF
standards track documents; it might also establish IETF policy for
such use.
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7. Security Considerations
Being text-based, protocols built with XML face significant threats,
including unintended disclosure, modification, and replay. Simple
passive attacks, such as packet sniffing, allow an attacker to
capture and view information intended for someone else. Captured
data can be modified and replayed to the original intended recipient,
with the recipient having no way to know that the information has
been compromised, detect modifications, be assured of the sender's
identity, or to confirm which protocol instance is legitimate.
Several security service options are available mitigate these risks.
Though XML does not include any built-in security services, other
protocols and protocol layers provide services that can be used to
protect XML protocols. XML encryption [12] provides privacy services
to prevent unintended disclosure. Canonical XML [6] XML digital
signatures [7] provide integrity services to detect modification and
authentication services to confirm the identity of the data source.
Other IETF security protocols (e.g., the Transport Layer Security
(TLS) protocol [2]) are also available to protect data and service
endpoints as appropriate. Given the lack of security services in
XML, it is imperative that protocol specifications REQUIRE additional
security services to counter common threats and attacks; the specific
required services will depend on the protocol's threat model.
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8. Acknowledgements
The authors would like to thank the following people who have
provided significant contributions to the development of this
document:
Josh Cohen and Andrew Newton.
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
1999.
[3] Alvestrand, H., "IETF Policy on Character Sets and Languages",
BCP 18, RFC 2277, January 1998.
[4] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[5] Murata, M., St.Laurent, S. and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[6] Boyer, J., "Canonical XML Version 1.0", RFC 3076, March 2001.
[7] Eastlake, D., Reagle, J. and D. Solo, "(Extensible Markup
Language) XML-Signature Syntax and Processing", RFC 3275, March
2002.
[8] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml,
October 2000, <http://www.w3.org/TR/2000/REC-xml-20001006>.
[9] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C
REC-xml-names, January 1999, <http://www.w3.org/TR/REC-xml-
names>.
[10] Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn, "XML
Schema Part 1: Structures", May 2001, <http://www.w3.org/TR/
xmlschema-1/>.
[11] Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes", May
2001, <http://www.w3.org/TR/xmlschema-2/>.
[12] Imamura, T., Dillaway, B., Schaad, J. and E. Simon, "XML
Encryption Syntax and Processing", October 2001, <http://
www.w3.org/TR/xmlenc-core/>.
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Informative References
[13] Backus, J., "The syntax and semantics of the proposed
international algebraic language of the Zurich ACM-GAMM
conference", June 1959.
[14] American National Standards Institute, "Code Extension
Techniques for Use with the 7-bit Coded Character Set of
American National Standard Code (ASCII) for Information
Interchange", ANSI X3.41, FIPS PUB 35, 1974.
[15] American National Standards Institute, "Information Retrieval:
Application Service Definition and Protocol Specification",
ANSI Z39.50, ISO Standard 23950, 1995.
[16] International Organization for Standardization, "Information
Processing Systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1)", ISO
Standard 8824, December 1990.
[17] International Organization for Standardization, "Information
Processing Systems - Open Systems Interconnection -
Specification of Basic Encoding Rules for Abstract Syntax
Notation One (ASN.1)", ISO Standard 8825, December 1990.
[18] International Organization for Standardization, "Information
processing - Text and office systems - Standard Generalized
Markup Language (SGML)", ISO Standard 8879, 1988.
[19] International Organization for Standardization, "Information
Technology - Universal Multiple-octet coded Character Set (UCS)
- Part 1: Architecture and Basic Multilingual Plane", ISO
Standard 10646-1, May 1993.
[20] Mealling, M., "The IETF XML Registry", draft-mealling-iana-
xmlns-registry-03 (work in progress), November 2001.
[21] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
Network Management Protocol (SNMP)", STD 15, RFC 1157, May
1990.
[22] Srinivasan, R., "XDR: External Data Representation Standard",
RFC 1832, August 1995.
[23] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
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[24] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[25] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June
1999.
[26] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646",
RFC 2781, February 2000.
[27] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
2001.
[28] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
C., Eisler, M. and D. Noveck, "NFS version 4 Protocol", RFC
3010, December 2000.
[29] Bray, T., Paoli, J. and C. Sperberg-McQueen, "Extensible Markup
Language (XML) 1.0", February 1998, <http://www.w3.org/TR/1998/
REC-xml-19980210/>.
[30] Lassila, O. and R. Swick, "Resource Description Framework (RDF)
Model and Syntax Specification", W3C REC-rdf-syntax, February
1999, <http://www.w3.org/TR/REC-rdf-syntax>.
[31] Williams, S. and M. Jones, "XML Protocol Abstract Model", July
2001, <http://www.w3.org/TR/xmlp-am/>.
[32] Suignard, M., Ishikawa, M., Duerst, M. and T. Texin, "Ruby
Annotation", May 2001, <http://www.w3.org/TR/ruby/>.
[33] Pemberton, S., "XHTML 1.0: The Extensible HyperText Markup
Language", January 2000, <http://www.w3.org/TR/xhtml1/>.
[34] W3C Communications Team, "XML in 10 points", November 2001,
<http://www.w3.org/XML/1999/XML-in-10-points/>.
[35] Gudgin, M., Hadley, M., Moreau, J. and H. Nielsen, "SOAP
Version 1.2 Part 1: Messaging Framework", December 2001,
<http://www.w3.org/TR/soap12-part1/>.
[36] Duerst, M. and A. Freytag, "Unicode in XML and other Markup
Languages", February 2002, <http://www.w3.org/TR/unicode-xml/
>.
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Authors' Addresses
Scott Hollenbeck
VeriSign, Inc.
21345 Ridgetop Circle
Dulles, VA 20166-6503
US
Phone: +1 703 948 3257
EMail: shollenbeck@verisign.com
Marshall T. Rose
Dover Beach Consulting, Inc.
POB 255268
Sacramento, CA 95865-5268
US
Phone: +1 916 483 8878
EMail: mrose@dbc.mtview.ca.us
Larry Masinter
Adobe Systems Incorporated
Mail Stop W14
345 Park Ave.
San Jose, CA 95110
US
Phone: +1 408 536-3024
EMail: LMM@acm.org
URI: http://larry.masinter.net
Hollenbeck, et al. Expires October 4, 2002 [Page 21]
Internet-Draft XML in IETF Protocols April 2002
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Hollenbeck, et al. Expires October 4, 2002 [Page 22]
