ndc shopping schema versioning and namespacing proposal

Simplifying the Business 1 Ó COPYRIGHT IATA 2013

To represent, lead and serve the airline industry

NDC 1.0 Publication: Schema VersioningOverview and NDC 1.0 Namespace Enhancement Proposal for IATA TAG


NDC 1.0 Publication Schema Design

SCHEMA DESIGN PRINCIPLESNDC 1.0 Publication: Schema Design & Versioning


NDC Schema Design Principles Scorecard

Design Principle NDC 1.0

Naming Standards Schema Library Strategy Documentation Standards Versioning Strategy Reuse Strategy

NDC 1.0 Publication Schema Design


NDC 1.0 Publication Schema Versioning

SCHEMA VERSIONINGNDC 1.0 Schema Design & Versioning



Business/ technical requirements drive new versions of schemas

Typical enhancements include adding and removing schema components

Good schema architectures increases compatibility

Repeatable versioning practice important

Schema Versioning Overview


XML Schema has no inherent notion of versioning

Schema can be enhanced in three ways Major Change (backward-incompatible) Minor Change (backward-compatible) Document Revisions (backward-compatible)

Enhancement type indicates schema compatibility1. Backward Compatibility2. Forward Compatibility


Schema Enhancement Versioning Overview


Backward-Compatibility Overview

The ideal schema enhancement design goalProvides backward-compatibility of the

schemas from one version to the nextThis is possible if you are only adding optional

new components and/or reducing restrictiveness

NDC 1.0 Publication Schema Compatibility



• Adding optional elements and attributes

• Making required elements and attributes optional

• Making occurrence constraints less restrictive

• Turning specific element declarations into choice groups

• Making simple types less restrictive

• Turning a simple type into a union

• Adding optional wildcards or open content

• Replacing element or attribute declarations with wildcards

• Turning a sequence group into an all group or a repeating choice group

Backward-Compatible Schema Changes



• Changing the order of elements or imposing an order

• Changing the structure of elements

• Removing any element or attribute declarations

• Removing wildcards or open content

• Changing the names of any elements or attributes

• Changing the target namespace of the schema

• Adding any required elements or attributes

• Making optional elements or attributes required

• Making occurrence constraints more restrictive

• Making simple types more restrictive

Backward-Incompatible Schema Changes


Forward Compatibility Overview

Part of an advanced schema design & versioning strategy

Forward-compatible schemas allow a version “2.1” instance to be valid according to the version “2.0” schema

Not provided in NDC 1.0 schema



Schema Versioning Best Practices

Version number format Two numbers separated by a period

“2” represents the major version number “1” represents the minor version number

Every schema has a version number Using both major and minor version

numbers Version number placement

Schema documents XML Instances Namespace names


2.0

2.1

2.2

backward-compatible

3.0

3.1

3.2

backward-compatible

backward-incompatible



NDC 1.0 Schema Versioning Scorecard

Versioning Method/ Practice NDC 1.0

Repeatable versioning practice Major/ Minor numbering format Version represented in schema documents Version represented in xml instances Version represented in namespace name



NDC 1.0 schema uses the @version attribute in schema preamble

NDC Version Representation in Schema Documents

Represents the version of the schema (e.g. vocabulary being described by the schema document)

Strictly for implementer documentation

XML Schema processor does not use it



NDC 1.0 Use of Schema Preamble @version Examples

setting description

<xsd:schema version=“0.9”> Pre-publication

<xsd:schema version=“1.0”> First publication

<xsd:schema version=“1.1”> Second publication: schema changed-compatibility kept

<xsd:schema version=“2.0”> Fourth publication: schema changed-compatibility lost



NDC 1.0 schema uses of the @id attribute in schema preamble

@id attribute represents publication version Represented as namespace

sub-location + 4 digit year + publication number

RQ/RS message schema contain the current publication id

Common (shared) schema contain the compatible publication range Range includes earliest to most

current compatible publication(s) No space included between

publication range

NDC Version Representation in Schema Documents



NDC 1.0 Use of Schema Preamble @id Examples

Description Message Schema Common Schema

First (schema compatible) publication

<xsd:schema id=NDC2014.1> <xsd:schema id=NDC2014.1>

Second (schema compatible) publication

<xsd:schema id=“NDC2014.2”> <xsd:schema id=“NDC2014.1NDC2014.2”>

Third (schema compatible) publication

<xsd:schema id=“NDC2014.1> <xsd:schema id=“NDC2014.1NDC2015.1”>

Break in publication compatibility

<xsd:schema id=“NDC2015.1> <xsd:schema id=“NDC2015.1NDC2015.2”>



NDC 1.0 schema includes a Version attribute in schema payload standard attributes

NDC Version Numbers in Instances

Allows implementers to specify schema version at root level of instance document


NDC 1.0 Publication Namespace Overview

NAMESPACE OVERVIEWNDC 1.0 Publication Versioning



Namespace Overview: In a Nutshell…

NDC implementer applications will tend to be complex

NDC itself combines elements from various document types

Two document types often have elements with the same name but different meanings and semantics

XML namespaces overcome this challenge and give developers a warm and fuzzy feeling



Namespace Purpose

To support combining various XML elements from different document types into one XML document

To provide a unique name that can be associated with a particular person or organization

Not to point to a location where a resource resides

NDC uses namespaces to enforce our personalized XML vocabulary… while allowing

implementers to do the same.

Traveler

Traveler



Namespace names are Uniform Resource Identifiers (URIs)

XML elements are given qualified names (QNames)

Attributes don’t use namespaces

Namespace Overview: How They Work

The xmlns attribute is used to specify each namespace prefix

IATA NDC Common Vocabulary Namespace

IATA NDC Message Namespace

W3C Namespace



Namespace Overview: How They Work

Namespace names are case-sensitive Two namespaces are

considered different if their capitalization is different

A namespace name should be unique

Namespace prefixes A namespace prefix serves

as a proxy for the namespace

“nc” is the namespace prefix for NDC Common and Simple Types

Namespace Prefix



Pre-Publication <xsd:schema targetNamespace=“http://www.iata.org/NDC” version=“0.9” id=“NDCBETA”>

First Publication <xsd:schema targetNamespace=“http://www.iata.org/NDC” version=“1.0” id=“NDC2014.1”>

Second Publication: schema changed, backward-compatible <xsd:schema targetNamespace=“http://www.iata.org/NDC” version=“1.1” id=“NDC2014.2”>

Third Publication: schema changed, backward-incompatible <xsd:schema targetNamespace=“http://www.iata.org/NDC” version=“2.0” id=“NDC2015.1”>

NDC 1.0: Current Use of Schema Namespace Examples

IATA URL NDC Service Domain

NDC Message Schema



Pre-Publication <xsd:schema targetNamespace=“http://www.iata.org/NDC/common” version=“0.9”

id=“NDCBETA”> First Publication

<xsd:schema targetNamespace=“http://www.iata.org/NDC/common” version=“1.0” id=“NDC2014.1”>

Second Publication: schema changed, backward-compatible <xsd:schema targetNamespace=“http://www.iata.org/NDC/common” version=“1.1”

id=“NDC2014.1NDC2014.2”> Third Publication: schema changed, backward-incompatible

<xsd:schema targetNamespace=“http://www.iata.org/NDC/common” version=“2.0” id=“NDC2015.1”>

NDC 1.0: Current Use of Schema Namespace Examples


NDC Common Vocabulary Identifier

NDC Common Schema


NDC NAMESPACE ENHANCEMENT PROPOSAL

NDC Schema Versioning with Namespacing

NDC 1.0 Publication Namespace Proposal



Current NDC Namespacing

http://www.iata.org/NDC

http://www.iata.org/IATA/NDC/common


NDC Common Vocabulary Identifier



Proposal: Include Major Version Number in NDC Namespace Name

Process Benefits

Make the version information an immediate property of the schema by only indicating the MAJOR version number in the namespace name

Makes the version information an immediate property of the schema

Desirable in the case of a major release where there is no intention of backward compatibility

Allows message (RQ/RS) versus common schema to be separately versioned and reflected in imported schema

Instantly breaks backward compatibility between schema versions

Supports life-cycle versioning of other NDC non-schema artifacts (e.g. WSDL)

Informs namespace aware applications that process instances need to change

Faster and easier routing for systems that handle multiple versions of one service as payload parsing not required

Note: Not used for minor releases as they are backward-compatible



NDC 1.0 Use of Version Number in Namespace Examples (1/2)

First publicationMessage schemaand common types share same version



NDC 1.0 Use of Version Number in Namespace Examples (2/2)

Subsequent publicationMessage schema enhancements are backward-compatible, but common types enhancements are backward-incompatible

ndc shopping schema versioning and namespacing proposal

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