The process can take a considerable amount of time, leaving. It generally means supporting previous versions of text in a newer consumer. Other applications may need a different rule as the. In some cases, we may change an existing object's behavior strateyy replacing it. The fundamental problem with most designs of a single version identifier in a document is that it usually doesn't provide for a given document to be valid under more than one version. As our definition of backwards compatibility specifies that the newer language's Defined Text Set must be versionong superset of the older language's Defined Text Set, the typical change is the addition xm, optional content into the newer version of the language. If your application is expecting a field to return.
Creating a new version of an XML Schema may have effects that ripple through. Managing these effects can be expensive. So it is worthwhile. Frequently, Schema versioning is considered in isolation from the rest of the system. Versionimg, as noted, Schema changes may impact other parts of a system, so we recommend that. Schema versioning be part of an integrated system evolution plan.
As a strategy for facilitating system evolution we focus on these three parts of a system - Schemas, instance. To treat these three parts in a holistic fashion we make the following recommendations: The rationale for each of these recommendations is explained over the course of this paper. But first we begin by defining the nature of the systems being targeted. Note: There are many other kinds of changes that could occur in an XML Schema than those. However, they are changes internal to the schema and have no manifestation in instance.
Most XML applications are "namespace aware". That is, the application is designed to process elements. For example, an XML Stylesheet Language Transformations XSLT Xml versioning strategy is an application which understands the XSLT namespace:. Changing xml versioning strategy results in breaking namespace-aware applications. This brings us to our. Suppose that a new version of a XML Schema is created using the same namespace, as described above.
And the versionijg version simply overwrites the old version. That is, the new version has the same filename and the same. URL xml versioning strategy as the old schema. Depending on the kinds of changes made, this may result in breaking all instance documents that were written to conform. A common occurrence xml versioning strategy creating a new version of an XML Schema is to change an element's content. Suppose that an application receives an instance document which conforms to the latest. And let's suppose that the application is still coded to the previous.
The application parses through the. How will the application. It would be useful if the application could consult the parser: "What's the type content model of. There are many possible courses of action that an application may take. Which action is taken depends on the application. How can we facilitate an application in recognizing an element's type? That is, how do we enable applications to.
Answer: the XML Schema syrategy be designed to. Instead, use named types. What is location's type? Answer: it is anonymous. This Schema is not. Instead, design your Schema like this:. Thus, this Schema is designed to facilitate an application. This will enable applications to query a parser for type information, e. If this is a type that the application did not expect i. As a parser validates strateyg instance document against a Schema, it collects. This collection of information is called.
Above we saw the motivation for using. The Schema declares this named type:. It is important to give a new name to location's type:. The reason is that we want to. That is, we want an application to see as many familiar elements and types as. The aircraftType is a familiar type. Versionning will find it useful to binary options empire an indication of whether it can expect changes as it processes.
This can be accomplished using a version. Note that this is what XSLT does. As the XSLT technology has migrated to a new version. If an instance document moving average trading signals a compound document - that is. A new version xml versioning strategy a Schema may make a change as simple as reordering the contents of an element. If an application is coded to expect a certain ordering of the data then the new version of the Schema will break the.
To avoid this an application should never depend on specific ordering of data. Applications should be designed to anticipate that the order of tags may change. Creating a new version of an XML Schema may result in removing an element or attribute. Versioninv application must decide whether the lack of the element or attribute is catastrophic or whether it can live. The action taken is application-specific and is outside the scope. Creating a new version of an XML Schema may result in adding an element or strateby.
The application strxtegy decide what to do with the xml versioning strategy information. The above recommendations will help mitigate breakage due to Schema changes. However, they do not. An old application may receive a new instance. To anticipate such occurrences it will be beneficial to institute a system protocol. To minimize impact to existing instance. Applications should be designed to anticipate that the order of tags may change - Define a system-wide protocol e.
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1.3 Kinds of Languages. There are different kinds of languages and the versioning approaches and strategies that are appropriate for one kind of language may not be.
This blog suggests the different web API versioning approaches and will suggest the best recommended approach from the author's experience.
Impact of XML Schema Versioning on System Design (Strategies for Facilitating System Evolution) by Roger L. Costello and Melissa Utzinger Introduction.