One document matched: draft-legg-xed-glue-00.txt
INTERNET-DRAFT S. Legg
draft-legg-xed-glue-00.txt Adacel Technologies
Intended Category: Standard Track D. Prager
Deakin University
August 7, 2003
XED: Schema Language Integration
Copyright (C) The Internet Society (2003). All Rights Reserved.
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Abstract
This document defines the means by which an Abstract Syntax Notation
One (ASN.1) specification can incorporate the definitions of types
and elements in specifications written in other Extensible Markup
Language (XML) schema languages. References to XML Schema types and
elements, RELAX NG named patterns and elements, and Document Type
Declaration element types are supported.
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Table of Contents
1. Introduction .................................................. 2
2. Conventions ................................................... 2
3. Representing Markup as ASN.1 Values ........................... 3
4. Supporting ASN.1 Types ........................................ 5
4.1 The AnyURI Type ........................................... 5
4.2 The NCName Type ........................................... 5
5. Referencing Foreign Types ..................................... 6
6. Referencing Foreign Elements .................................. 8
7. Security Considerations ....................................... 9
8. Acknowledgements .............................................. 10
9. Normative References .......................................... 10
10. Informative References ....................................... 11
11. Intellectual Property Notice ................................. 11
12. Copyright Notice ............................................. 11
13. Authors' Addresses ........................................... 12
Appendix A. ASN.1 for Schema Language Integration ................ 12
1. Introduction
This document defines the means by which an Abstract Syntax Notation
One (ASN.1) [X680] specification can incorporate the definitions of
types and elements in specifications written in other Extensible
Markup Language (XML) [XML] schema languages. References to
XML Schema [XSD1] types and elements, RELAX NG [RNG] named patterns
and elements, and Document Type Declaration (DTD) [XML] element types
are supported.
Non-ASN.1 definitions are supported by first defining an ASN.1 type
whose values can contain arbitrary markup, and then defining
constraints on that type to restrict the content to specific
nominated datatypes from non-ASN.1 schema definitions.
The ASN.1 definitions in this document are consolidated in
Appendix A.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
to be interpreted as described in RFC 2119 [BCP14]. The key word
"OPTIONAL" is exclusively used with its ASN.1 meaning.
This specification makes use of definitions from the XML Information
Set (Infoset) [ISET]. The term "element" shall be taken to mean an
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Infoset element information item. The term "attribute" shall be
taken to mean an Infoset attribute information item.
A reference to a ASN.1 production [X680] (e.g. UserDefinedConstraint)
is a reference to the text in an ASN.1 specification corresponding to
that production.
3. Representing Markup as ASN.1 Values
A value of the AnyType ASN.1 type holds arbitrary content of an
element (but not the start-tag and end-tag, or empty-element tag),
plus the context required to correctly interpret that content.
AnyType ::= SEQUENCE {
prolog [0] UTF8String (SIZE(1..MAX)) OPTIONAL,
context [1] UTF8String (SIZE(1..MAX)) OPTIONAL,
attributes [2] UTF8String (SIZE(1..MAX)) OPTIONAL,
content [3] UTF8String (SIZE(1..MAX)) OPTIONAL
}
With respect to some element whose content is represented by a value
of the AnyType type:
- the prolog component of the value contains, from the XML document
containing the element, the text corresponding to the prolog
production [XML], or the sufficient (well-formed and valid) part
thereof to define the entity references appearing in the context,
attributes and content components of the value,
- the context component of the value contains a whitespace separated
list of the [namespace attributes] of the ancestors of the
element, if any, plus any [attributes] of the ancestor elements
which are inherited by their element children,
- the attributes component of the value contains text corresponding
to the [attributes] of the element, if any,
- the content component of the value contains the text of the
content of the element between the start-tag and end-tag. The
component is absent if there are no characters between the
start-tag and end-tag, or if the element uses an empty-element
tag.
Leading and trailing whitespace corresponding to the S production
[XML] in the prolog, context and attributes components MAY be
omitted. Multiple whitespace characters corresponding to the S
production in the prolog, context and attributes components MAY be
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replaced with a single space character.
Any entity references in the context, attributes and content
components MAY be replaced by their replacement text so that the
prolog component can be omitted.
If the prolog component is absent then XML version 1.0 is assumed.
Note that the Directory XML Encoding Rules [DXER] have special
provisions for encoding values of the AnyType type. For other
encoding rules, values of the AnyType type are encoded according to
the ASN.1 type definition of AnyType.
Example
Consider the following XML document:
<?xml version='1.0'?>
<!DOCTYPE root [
<!ENTITY TRUE 'true'>
]>
<root xmlns:ns="http://www.example.com/SLI">
<example ns:foo="1" bar="0">
<this>&TRUE;</this>
<that/>
</example>
</root>
The AnyType value corresponding to the content of the <example>
element is, in ASN.1 value notation [X680]:
{
prolog { "<?xml version='1.0'?>", lf,
"<!DOCTYPE root [", lf
" <!ENTITY TRUE 'true'>", lf
"]>", lf },
context "xmlns:ns=""http://www.example.com/SLI>""",
attributes " ns:foo=""1"" bar=""0""",
content { lf,
" <this>&TRUE;</this>", lf,
" <that/>", lf, " " }
}
The following AnyType value is also an acceptable representation of
the content of the <example> element:
{
context "xmlns:ns=""http://www.example.com/SLI>""",
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attributes "bar=""0"" ns:foo=""1""",
content { lf,
" <this>true</this>", lf,
" <that/>", lf, " " }
}
By itself the AnyType ASN.1 type imposes no datatype restriction on
the markup contained by its values, and is therefore analogous to the
XML Schema anyType [XSD1].
There is no ASN.1 notation that can directly impose the constraint
that a value of the AnyType type must conform to the markup allowed
by a specific non-ASN.1 definition. However, UserDefinedConstraint
notation can be exploited to provide parameters to nominated
predefined constraints that have the desired effect. A predefined
constraint is identified by an OBJECT IDENTIFIER value passed as a
parameter in a UserDefinedConstraint.
Though the UserDefinedConstraint notation does not express the
semantics of a constraint, multi-schema aware ASN.1 tools can
recognize particular OBJECT IDENTIFIER values (defined later in this
document) and behave appropriately. These OBJECT IDENTIFIER values
have id-constraint as a common prefix.
id-constraint OBJECT IDENTIFIER ::=
{ iso(1) 2 36 79672281 xed(3) constraint(1) }
4. Supporting ASN.1 Types
The section defines ASN.1 types that support the application of
constraints on the markup allowed in values of the AnyType ASN.1
type.
4.1 The AnyURI Type
A value of the AnyURI ASN.1 type is a URI character string [URI].
AnyURI ::= UTF8String (CONSTRAINED BY
{ -- conforms to the format of a URI -- })
4.2 The NCName Type
A value of the NCName ASN.1 type is a character string conforming to
the NCName production of Namespaces in XML [XMLNS].
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NCName ::= UTF8String (CONSTRAINED BY
{ -- conforms to the NCName production of
-- Namespaces in XML -- })
5. Referencing Foreign Types
To incorporate a non-ASN.1 datatype into an ASN.1 specification it is
necessary to constraint values of the AnyType ASN.1 type to contain
only markup valid with respect to that datatype.
XML Schema and RELAX NG both have distinct definitional forms for
elements and types (named patterns in RELAX NG). A DTD element type
declaration can be regarded as defining either a complete element, or
the content of an element (i.e. a type).
The values of the AnyType ASN.1 type can be restricted to conform to
a specific XML Schema named type or RELAX NG named pattern, or to
conform to the content specified by a nominated DTD element type
declaration, by applying a UserDefinedConstraint containing the value
of id-constraint-xml-type as a parameter.
id-constraint-xml-type OBJECT IDENTIFIER ::= { id-constraint 0 }
A UserDefinedConstraint in which an OBJECT IDENTIFIER with the value
of id-constraint-xml-type is used MUST satisfy all of the following
conditions:
a) there SHALL be three or four UserDefinedConstraintParameters,
b) the first UserDefinedConstraintParameter SHALL be a Value of the
OBJECT IDENTIFIER ASN.1 type and that Value SHALL be the same as
id-constraint-xml-type,
c) the second UserDefinedConstraintParameter SHALL be a Value of the
AnyURI ASN.1 type (possibly an empty string),
d) the third UserDefinedConstraintParameter SHALL be a Value of the
NCName ASN.1 type,
e) the fourth UserDefinedConstraintParameter, if present, SHALL be a
Value of the AnyURI ASN.1 type,
f) taken together the second and third UserDefinedConstraintParameter
SHALL be the namespace name and local name [XMLNS] of either an
XML Schema type definition, a RELAX NG named pattern, or a DTD
element type declaration.
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The fourth UserDefinedConstraintParameter is used when the namespace
name and local name reference is ambiguous, i.e. refers to
definitions in more than one schema document. This situation would
occur, for example, when importing types with the same name from
independently developed XML Schemas defined without a target
namespace. The value of the fourth UserDefinedConstraintParameter is
a URI that indicates the intended schema document, either an
XML Schema specification, a RELAX NG specification, or a DTD.
Example
AnyType (CONSTRAINED BY {
OBJECT IDENTIFIER:
{ iso(1) 2 36 79672281 xed(3) constraint(1) 0 },
AnyURI:"http://www.w3.org/2001/XMLSchema",
NCName:"decimal" })
The XML-Type and XML-Type-From-Schema parameterized types [X683] are
defined so that XML Schema named types, RELAX NG named patterns and
DTD element type declarations can be more conveniently referenced.
XML-Type { AnyURI:namespace, NCName:name } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-type,
AnyURI:namespace, NCName:name })
XML-Type-From-Schema { AnyURI:namespace, NCName:name,
AnyURI:schemaIdentity } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-type,
AnyURI:namespace, NCName:name, AnyURI:schemaIdentity })
For example, the following notation is sufficient to incorporate the
xsd:decimal XML Schema type as the member type in a SEQUENCE OF type
definition:
SEQUENCE OF number
XML-Type { "http://www.w3.org/2001/XMLSchema", "decimal" }
Note that the ASN.1 Schema [ASD] translation of this ASN.1 type
provides a more natural way to reference the XML Schema decimal type:
<type xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<sequenceOf/>
<element name="number" type="xsd:decimal"/>
</sequenceOf>
</type>
The XML-Type parameterized type cannot be used if the URI of a schema
document is required to disambiguate the namespace name and local
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name.
6. Referencing Foreign Elements
ASN.1 does not have a construct analogous to a global element
definition, hence there is no analogy in ASN.1 for referencing a
global element definition (though there is in ASN.1 Schema).
The AnyType ASN.1 type represents the content of an element. To
import an element from a non-ASN.1 specification it is necessary to
regard that element as the child element of a notional type whose
content model permits only the imported element.
The notional type is arbitrarily chosen to be a choice type.
The notional type does not have any attributes therefore the
attributes component of a value of AnyType would normally be empty,
or contain only namespace declaration attributes.
The values of the AnyType ASN.1 type can be restricted to conform to
a notional choice type containing a specific XML Schema element or
RELAX NG element, or containing an element with the name and content
specified by a nominated DTD element type declaration, by applying a
UserDefinedConstraint containing the value of
id-constraint-xml-element as a parameter.
id-constraint-xml-element OBJECT IDENTIFIER ::= { id-constraint 1 }
A UserDefinedConstraint in which an OBJECT IDENTIFIER with the value
of id-constraint-xml-element is used MUST satisfy all of the
following conditions:
a) there SHALL be three or four UserDefinedConstraintParameters,
b) the first UserDefinedConstraintParameter SHALL be a Value of the
OBJECT IDENTIFIER ASN.1 type and that Value SHALL be the same as
id-constraint-xml-element,
c) the second UserDefinedConstraintParameter SHALL be a Value of the
AnyURI ASN.1 type (possibly an empty string),
d) the third UserDefinedConstraintParameter SHALL be a Value of the
NCName ASN.1 type,
e) the fourth UserDefinedConstraintParameter, if present, SHALL be a
Value of the AnyURI ASN.1 type,
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f) taken together the second and third UserDefinedConstraintParameter
SHALL be the namespace name and local name [XMLNS] of either an
XML Schema element definition, a RELAX NG element definition, or a
DTD element type declaration.
The fourth UserDefinedConstraintParameter is used when the namespace
name and local name reference is ambiguous. Its value is a URI that
indicates the intended schema document, either an XML Schema
specification, a RELAX NG specification, or a DTD.
Example
AnyType (CONSTRAINED BY {
OBJECT IDENTIFIER:
{ iso(1) 2 36 79672281 xed(3) constraint(1) 1 },
AnyURI:"http://www.example.com/IPO",
NCName:"purchaseOrder" })
The Contained-XML-Element and Contained-XML-Element-From-Schema
parameterized types are defined so that XML Schema global elements,
RELAX NG elements and DTD element type declarations can be more
conveniently referenced.
Contained-XML-Element
{ AnyURI:namespace, NCName:name } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-element,
AnyURI:namespace, NCName:name })
Contained-XML-Element-From-Schema { AnyURI:namespace, NCName:name,
AnyURI:schemaIdentity } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-element,
AnyURI:namespace, NCName:name, AnyURI:schemaIdentity })
The Contained-XML-Element type cannot be used if the URI of a schema
document is required to disambiguate the target namespace and name.
7. Security Considerations
Values of the AnyType type potentially hold the content of elements
for which the Canonical XML [CXML] representation must be
recoverable. Such recovery is needed for the verification of digital
signatures. The rules governing the representation of the content of
an element in an AnyType value are compatible with Canonical XML.
Implementors must be careful not to introduce any further changes
which would make it impossible to recover the Canonical XML
representation.
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8. Acknowledgements
This document and the technology it describes are a product of a
joint research project between Adacel Technologies Limited and Deakin
University on leveraging existing directory technology to produce an
XML-based directory service.
9. Normative References
[BCP14] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[URI] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[DXER] Legg, S. and D. Prager, "Directory XML Encoding Rules for
ASN.1 Types", draft-legg-xed-dxer-xx.txt, a work in
progress, August 2003.
[X680] ITU-T Recommendation X.680 (07/02) | ISO/IEC 8824-1:2002,
Information technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation
[X683] ITU-T Recommendation X.683 (07/02) | ISO/IEC 8824-4:2002,
Information technology - Abstract Syntax Notation One
(ASN.1): Parameterization of ASN.1 specifications
[XML] Bray, T., Paoli, J., Sperberg-McQueen, M. and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
Recommendation, http://www.w3.org/TR/2000/REC-xml-20001006,
October 2000.
[XMLNS] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML",
http://www.w3.org/TR/1999/REC-xml-names-19990114, January
1999.
[ISET] Cowan, J. and R. Tobin, "XML Information Set", W3C
Recommendation, http://www.w3.org/TR/2001/REC-xml-
infoset-20011024, October 2001.
[CXML] Boyer, J., "Canonical XML Version 1.0", W3C Recommendation,
http://www.w3.org/TR/2001/REC-xml-c14n-20010315, March 2001.
[XSD1] Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn, "XML
Schema Part 1: Structures", W3C Recommendation,
http://www.w3.org/TR/2001/REC-xmlschema-1-20010502, May
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2001.
[RNG] Clark, J. and M. Makoto, "RELAX NG Tutorial", OASIS
Committee Specification, http://www.oasis-
open.org/committees/relax-ng/tutorial-20011203.html,
December 2001.
10. Informative References
[BCP11] Hovey, R. and S. Bradner, "The Organizations Involved in the
IETF Standards Process", BCP 11, RFC 2028, October 1996.
[ASD] Legg, S. and D. Prager, "ASN.1 Schema: An XML Representation
for ASN.1 Specifications", draft-legg-xed-asd-xx.txt, a work
in progress, August 2003.
11. Intellectual Property Notice
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. [BCP11]
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementors or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
12. Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
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and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
13. Authors' Addresses
Dr. Steven Legg
Adacel Technologies Ltd.
250 Bay Street
Brighton, Victoria 3186
AUSTRALIA
Phone: +61 3 8530 7710
Fax: +61 3 8530 7888
EMail: steven.legg@adacel.com.au
Dr. Daniel Prager
C/o Professor Lynn Batten
Department of Computing and Mathematics
Deakin University
Geelong, Victoria 3217
AUSTRALIA
EMail: dan@layabout.net
EMail: lmbatten@deakin.edu.au
Appendix A. ASN.1 for Schema Language Integration
This appendix is normative.
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SchemaLanguageIntegration
{iso(1) 2 36 79672281 xed(3) module(0) sli(1)}
-- Copyright (C) The Internet Society (2003). This version of
-- this ASN.1 module is part of RFC XXXX; see the RFC itself
-- for full legal notices.
DEFINITIONS
IMPLICIT TAGS EXTENSIBILITY IMPLIED ::= BEGIN
EXPORTS AnyType, AnyURI, NCName,
XML-Type{}, XML-Type-From-Schema{},
Contained-XML-Element{};
AnyType ::= SEQUENCE {
prolog [0] UTF8String (SIZE(1..MAX)) OPTIONAL,
context [1] UTF8String (SIZE(1..MAX)) OPTIONAL,
attributes [2] UTF8String (SIZE(1..MAX)) OPTIONAL,
content [3] UTF8String (SIZE(1..MAX)) OPTIONAL
}
AnyURI ::= UTF8String (CONSTRAINED BY
{ -- conforms to the format of a URI -- })
NCName ::= UTF8String (CONSTRAINED BY
{ -- conforms to the NCName production of
-- Namespaces in XML -- })
id-constraint OBJECT IDENTIFIER ::=
{ iso(1) 2 36 79672281 xed(3) constraint(1) }
id-constraint-xml-type OBJECT IDENTIFIER ::= { id-constraint 0 }
id-constraint-xml-element OBJECT IDENTIFIER ::= { id-constraint 1 }
XML-Type { AnyURI:namespace, NCName:name } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-type,
AnyURI:namespace, NCName:name })
XML-Type-From-Schema { AnyURI:namespace, NCName:name,
AnyURI:schemaIdentity } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-type,
AnyURI:namespace, NCName:name, AnyURI:schemaIdentity })
Contained-XML-Element
{ AnyURI:namespace, NCName:name } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-element,
AnyURI:namespace, NCName:name })
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Contained-XML-Element-From-Schema { AnyURI:namespace, NCName:name,
AnyURI:schemaIdentity } ::= AnyType
(CONSTRAINED BY { OBJECT IDENTIFIER:id-constraint-xml-element,
AnyURI:namespace, NCName:name, AnyURI:schemaIdentity })
END
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