Impact of XML Schema Versioning on System Design

Xml schema versioning strategy.

eBay Schema Versioning Strategy

Multiple generational versioning The versioning mechanism must allow for multiple generations of versioning. This document focuses on the versioning of XML Schemas. The desired behaviour of schema processors is the subject of these use cases. For backward compatibility: The precedence of the fallbacks, when more than one is used, needs to be defined.

The System We assume that the system under consideration possesses these characteristics: In some cases, non-technical reasons may influence whether a version is minor or major e. The old applications that used schema B should not treat instances of W as instances of B, otherwise they will be interpreting the data incorrectly.

This use case uses the situation of a convenience store with a cash register, price management system and fuel pumps. Schema versioning is also important to other types of systems, such as for the application and for code generators using XML Schemas.

In object oriented programming languages, the concept of inheritance can be used to create a new class based on an existing class.

XML Schema Versioning Use Cases

Consider a convenience store, with a point-of-sale POS cash register that receives product data from various devices in the store. The application could be written in many different ways.

The standard desired behaviour. However, they will will reject bad messages. The system processes it using schema W. That is, the new version has the same filename and the same URL location as the old schema. The price management system generates an instance of the price management schema. The old inventory system processes an instance that has a major version change.

Hence, versioning mechanisms in XML Schema should new versions to be created, and the schema processors need to handle instances defined by the different versions. An instance of the specialized schema will be processed according to the specialized schema. Object-oriented 2. It would be useful if the application could consult the parser: Object Deprecation Example Let's suppose eBay offers a new "flavor" feature, and then later enhances the feature in a way that isn't backward compatible.

The most common action is schema validation, where an instance document is validated against a XML Schema. A third vendor produces cash registers. Consider an application that has not been sekolah forex di jogja to the new version, and receives an instance document that conforms to the new version.

The only change is the addition of an optional editor element.

Status of this Document

Valid against the base schema. Due to market forces and competition between the vendors, there is no single standard data schema that they all use. Common requirements 1. So it is worthwhile to examine ways to mitigate the costly ripple effects of new versions of a Schema. Schemas will be identified by a letter, for example "B". See eBay's Version Support Schedule.

Schema Versioning Strategy - eBay Trading API

For example, there could be a customer subclass derived from the person class, but a customer is not an employee. Here's what happens xml schema versioning strategy the API: The processor indicates that instances which are schema valid against F are also always valid against V.

To treat these three parts in a holistic fashion we make the following recommendations: This scenario is the same as Scenario A, except that the price management system has been replaced by the fuel pump.

Multiple branch versioning The versioning mechanism must allow for more than one version to be independently created, and those versions to also have multiple versions. Overview In this use case a schema is versioned many times. Existing schema processors do not perform this function. Although it does not know about sekolah forex di jogja, it accepts it because an employee is a version of a person.

For example, at any time, API calls may return new elements in addition those declared in the version of the schema you are using. Instead, design your Schema like this: Fallbacks specified in the schema. It constraints the units of both measurments to be mmHg. You should design your software to be able to handle or gracefully ignore extra elements that we add to the schema.

Schema versioning is one of the drivers for system evolution.

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The alternative fallback behaviour could be specified in a number of different places. That is, the application is designed to process elements belonging to a specific namespace. The processor might be able to easily determine that the instance is a person from looking at the element name.

This document describes the desirable behaviours for use cases that involve XML Schema versioning.

The System

The XML Schema is periodically updated, i. The schema for this will be called forexct location F. A senior manager instance is submitted into the payroll service.

And the new version simply overwrites the old version. Recommendation 5: A version of a schema may be versioned again. The output from the price management system is sent in error to the fuel volume tracker.

XML Schema Versioning Use Cases

Polymorphism is one of the key features of object oriented programming: We want to preserve this familiarity. Define a system-wide protocol e. An employee instance is submitted into the user database service. The GP processor determines that it is an instance of the base schema.

This use case has illustrated the operation of testing if the set of documents described by one work from home nurse jobs louisville ky is a subset of the set described by a different schema. In this case it is a user database, which can accept any type of person explain options trading includes employees, managers and senior managers.

Another GP system generates an instance of the specialized schema. The semantics of an element does not change with new versions of the Schema.

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You may receive a warning in the response. Overview This use case mimics the inheritance and polymorphic behaviour of object oriented programming languages. The systems integrators now know that the output from the xml schema versioning strategy management system is not compatiable with the volume tracker. Overview In this use case, schemas are specialized with more specific versions and information items are renamed in those versions.

That is, which version of schema the instance correspond to. The hospital system processs the refined instance. An example instance of B is: To prevent breaking old instance documents give the new Schema version a different filename or a different URL location or both.

As a strategy for facilitating system evolution we focus on these three parts of a system - Schemas, instance documents, and applications.

The hospital system processs the base instance. But first we begin by defining the nature of the systems being targeted. The schema validator indicates that the document is valid against the cash register schema. The old inventory system processes an instance that has a minor version change. The system identifies that it is a minor version of B. By "not supported", we mean that the deprecated object will no longer work, and eBay will not address issues you report related to the deprecated object or functionality.

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