XVIF: Decoding XML Validation Interoperability Framework

Introduction to XVIF

XVIF is a framework which has been developed to address the issue of interoperability between XML validators. This is because it offers a uniform method through which all the validators can relay validation information that can be well understood by the other validators and tools in XML.

The goal of this frmaework is to enable XML documents to be validated once and then the validation information can be reused later without having to revalidate the document. It helps prevent duplicate validation which can be detrimental to the application. It also seeks to encourage component-based validation where different validators and tools can be used in the process.

What is XVIF?

XVIF (XML Validation Interoperability Framework) is the name given to the set of rules for the standardized validation of XML documents. It offers the definition of the validation rules in a framework with the notations to express the rules and tools to run the validation against the XML documents. The intent is to enable XML validators to support a standard validation definition language and processing model to ensure that documents can be validated by many parsers and platforms at the same time.

Things to Know About XVIF

It is an XML based framework that facilitates the interoperability between different XML validators as well as parsing libraries. Here are some key things to know about XML Validation Interoperability Framework:

Purpose: As the name suggests, it is designed to help developers switch from one XML validator or parser to another without having to alter their code. This makes it easier to update/switch XML processing libraries.
Standardized Tests: This framwork specifies a set of standardized test cases and test script frameworks for determining compliance with XML specifications. A good level of conformance is in fact indicated by passing the XVIF test suite for an XML validator or library.
Encourages Interoperability: Since it defines a test suite and set of test cases that are to be used for XML processing libraries, the various XML processing libraries can interoperate more efficiently. This is an indication that libraries that have been tested using XML Validation Interoperability Framework are more inclined to parse and process XML in a standard manner.
Work done by Members of W3C: XML Validation Interoperability Framework was created by many W3C members, some of which are main contributors to XML standards and implementations. This assists in gaining wide ranging input into the requirements.
Covers Critical XML Areas: These frameworks are at the moment limited to testing conformance to XML 1.0 and 1.1 with respect to components that include parsers, schemas, XPath engines and validators. These are central to XML processing.

All in all, the XML Validation Interoperability Framework is designed to enhance the level of standardization and interoperability of XML libraries and tools. By encouraging common test case and compatibility, it ensures that handling of XML is done in a similar manner across implementations.

How Does It Work?

The key components that enable XVIF’s interoperable validation capabilities are:

XSEF Rules: XSEF (XML Structural Expectations Framework) is a language specially designed to define what makes an XML document structurally valid. XSEF rules define entities such as mandatory attributes, types of data, cardinality of relation, etc.
XVIF Processor: This software takes XSEF rules and checks the XML document against these rules. In addition, there are many standard processors available such as Apache XVIF and Sun XVIF to offer cross platform validation.
XRI Reports: The results are then printed out in a structured format known as XRI for XML Rules Interpretation where any errors such as missing tags, type conversion errors etc. are displayed if present.

XML Validation Interoperability Framework Example

Here is the simplest XML file as follows, an XSEF rule as follows and sample validation as follows.

XML File:

<person>
<name>John</name>
<age>Twenty</age>
</person>

XSEF Rule:

<xf:require-element name=”age” type=”integer”/>

This rule specifies that the “age” element must have an integer type.

When validated against the XSEF rule with the help of an XVIF processor it would generate a failure XRI report as the number “Twenty” is not an integer.

Key Capabilities Provided by XVIF

Some of the key capabilities provided by the XML Validation Interoperability Framework include:

Basic validation trigger information: Enables the validator to know what type of validation is being asked (for instance, schema validation).
Standard expression of validation outcomes: This is a format through which validators can relay validation results, errors, and warnings.
Validation metadata: This is used to add information about validation like the schema/tools used.
Specialization artifacts: These enable the validators to include or link to any validation-related data within the XML document.
Conformance identification: Enables the validators to provide a declaration of the extent of their implementation of the XVIF standard.

Understand XVIF Validation with Examples

Validation Triggers

XML Validation Interoperability Framework is for generating validation requests in a standardized manner that all conforming validators and tools will be able to interpret. This makes it possible for components to inform others what validation is expected without having to know the specifics of the proprietary validation.

It defines standard validation trigger information that can be embedded within XML documents:

xvif:validate elements: used to request document or component validation against schemas or other requirements. Provides details of validity that is expected and the possibilities.
xvif:validationRoot elements: Refers to parts of documents that contain a validation root so that only partial validation can occur.
xvif:useValidator elements: It points to the validator that should be used, using the XVIF conformance URI.

If a validator comes across this standard trigger information, it must validate as per this standard trigger information. Tools can also comprehend such triggers and inform the validators about validation needs.

Here is an example xvif:validate element requesting XSD schema validation:

<xvif:validate xvif:type=”schema”/>

Validation Outcomes

Since the validation information needs to be communicated between the validators, there must be a means of passing the validation results, error, and warnings.

This framwork defines structures for expressing validation messages in a standard format consisting of:

A message identifier: An identification number for the specific message type.
Message type: Whether the message is an error, warning etc.
A message body: Additional information about the validation problem in a language comprehensible by a human being.
Message metadata: Extra information about the message in a structured format.

Here is an example of an XML Validation Interoperability Framework formatted validation message:

<xvif:validationMessage
xvif:messageId=”err-attribute-invalid”
xvif:severity=”error”>
<xvif:messageBody>

One of such restrictions is that the ’unknownAttr’ attribute is not allowed on the ‘document’ element.

</xvif:messageBody>
<xvif:messageMeta>
<xvif:location xvif filePath=”doc.xml”>
<xvif:elementName>document</xvif:elementName>
</xvif:location>
</xvif:messageMeta>
</xvif:validationMessage>

This offers sufficient information to both the human and the machine for a comprehensive understanding of the validation concern to warrant corrective action.

Since this format is standardized, such message can be:

Returned directly in validation outputs.
Stored as XML files which serve as artifacts located in the XML source documents
Used by validators in one interface and received from validators in another.

Validation Metadata

It also offers the ability to describe the validation, through additional metadata, as having standard validation triggers and outcomes.

This allows detailed information such as the following to be added:

Additional information about the validator involved and the version used during the evaluation.
The schemas or definitions that are used for validation.
Levels of conformance regarding to XML Validation Interoperability Framework or other specifications.
Electronic signed statements from reliable third parties on the status of validation.
Timestamps specifying validity intervals for the cached validation results.

Here is an example of validation metadata being added:

<xvif:validationMetadata>
<xvif:validator>
<xvif:name>My Validator</xvif:name>
<xvif:version>1.2.0</xvif:version>
</xvif:validator>

<xvif:conformsTo>
<xvif:specUri>http://xvif.org/1.0</xvif:specUri>
<xvif:conformance>xvif-processor</xvif:conformance>
</xvif:conformsTo>

</xvif:validationMetadata>

This kind of metadata proves useful in understanding and documenting the origins of validation.

Validation Artifacts

In some cases, validation-related information has to be closely linked with the actual XML document content – encoded into the files being validated.

XML Validation Interoperability Framework supports this through Validation Artifacts which allow elements covering:

Validation messages
Use of other external sources of validation
Electronic markers of validation status

To be included in the XML documents as a part of the content that needs to be transported.

For example, validation messages can be included at the locations they apply:

This links the validation information to content without disconnecting them even if passed through files.

Conformance Identification

The XVIF specification defines multiple conformance profiles that implementations may adhere to:The XVIF specification defines multiple conformance profiles that implementations may adhere to:

xvif-processor: This component processes validation triggers and performs validation.
xvif-interop: Interacts with other components in exchanging validation messages.
xvif-packaging: Incorporates/extracts the validation artifacts into the files.

Validators and tools can know how they conform to the norm by checking the URI that characterizes the target conformance profile.

For example:

<xvif:conformsTo>
<xvif:specUri>http://xvif.org/1.0/xvif-processor</xvif:specUri>
</xvif:conformsTo>

This makes it possible for implementations to declare and find out which of the XVIF capabilities are supported to create compatibility.

Key Features of XVIF

The XML Validation Interoperability Framework offers various features include:

Portability: Enables the same validation rules and processors to be implemented in various software systems and XML parsers.
Extensibility: XSEF gives the possibility to add validation rules for one or more vocabularies that have been developed for specific purposes.
Modularity: Rules can be used repeatedly as well as integrated with other rules in a free form manner.
Human Readability: XSEF rules’ objectives are to present constraints in a form that is understandable.
Formality: The validations are specified in a well-specified language of the consensus protocol.
Standardization: XVIF is an OASIS open standard and several vendors and tools support it.

Components of XVIF

The main components that make up the XVIF framework are:

XSEF Language: The specialized language for specifying XML structural expectations & validation rules.
XSEF Vocabulary: Common terms that are employed in formulation of XSEF rules.
XSEF Schema: Describes the syntactical rules used in constructing XSEF expressions.
XVIF Processors: Software that uses XSEF rules and checks the correctness of XML with respect to them.
XRI Reports: Tabular reports that describe validation failures.
XVIF APIs: APIs which allow other systems to leverage XVIF validation functionalities.

Benefits of Using XVIF

Applying the XML Validation Interoperability Framework can provide several important benefits:

Reusable Validation Logic: Once the XSEF rules are defined, these can be used to validate documents in any environment.
Reduced Custom Coding: There is less reliance on proprietary custom-coded validations.
Interoperability: It allows validation to be conducted in a similar manner across different systems and organizations.
Composition: Permits flexible assembly of validation rules to create complex desired combinations.
Readability: Helps to gain a clearer vision of the structural expectations for XML.
Maintainability: Makes it easier to edit and maintain the validation logic over time.
Vendor Neutrality: Prevents being locked into any specific vendor XML validation implementation.

Applications of XVIF

It is universally applicable across many usage scenarios that involve validating structured XML data, including:

Verifying document-oriented XML information models.
The process of ensuring that data exchange files that pass between systems are accurate.
Guards of data feeds consumed across organizations for maintaining their integrity.
XML transactions are validated on the server side.
Control logic in tools for XML developers.
Integration of validation features in XML storage media.
To better ensure the long-term governance of validation expertise, more systematic methods of capturing such knowledge are required.

Uses of XVIF

More specific use cases and adoption patterns for applying XVIF include:

Authoring Centralized Validation Rules: XML architects can also become responsible for defining and managing XSEF rules as an enterprise resource.
Validating Web Services: XSEF rules can be applied for validating the XML within the SOAP and REST web services.
Continuous Integration Testing: Such validation increases the reliability and compatibility of CI builds and test automation.
XML Publishing: With help of the XSEF-driven auto-validation, technical publishers can enrich the authoring tools.
XML Content Management: XSEF is used together with XML content models in content management systems.
Data Migration Validation: This framework can migrate XML structures across systems by offering self-describing validation logic.

Challenges of Using XVIF

While the XML Validation Interoperability Framework delivers important benefits, adopting XVIF also comes with some challenges, such as:

Learning Curve: Authors and developers have to use XSEF language for describing validation rules.
Tooling Gaps: The tool stacks required for XSEF development remain a work in progress as vendors continue to tweak these environments to support the various XSEF development life cycles.
Complex XML Models: Very complicated XML schemes are rather complicated when it comes to description in XSEF only.
Custom Validation Logic: Additional domain validation which is not included in XSEF must be programmed.
Performance Overhead: Extra validation processing can also contribute to the performance delay if not well optimized.
Governance Overhead: The management of validation rules is a critical process that must be governed well to work as planned.

Wrapping Up

With increased usage of XML in exchange of large volumes of mission critical data in various systems, it is important to have standard validation tools to ensure that the systems remain intact and the information is not lost or corrupted during transmission.

The XML Validation Interoperability Framework offers an open specification for different enclosures and application of validation rules across parsers, platforms, and organizations.

The XML Validation Interoperability Framework provides:

Typical response triggers for the initiation of validation.
Some of the common formats of validation results.
The validation details exchanged between connected modules are also accompanied by metadata.
Validation artifacts that are incorporated in the document.
Conformance to XVIF advertising.

Enhancing these capabilities enables XML validators and tools to enhance interoperation – avoiding the re-occurrence of validation and encouraging reuse of validation between components.

Hence, the normalization of these validation communication mechanisms becomes crucial to organizing validation concerns in today’s large-scale XML environments.

Frequently Asked Questions

Is there a need to learn a specific programming language for using XVIF?

No, XVIF validation capabilities can be invoked from any environment through the available processors. However, XSEF rules themselves are based on XML notation.

Is it possible to integrate XVIF into our current custom validation script?

Yes, extension mechanisms and APIs provided by XVIF SDK can be used for additional programming that enhances or extends XSEF validation.

Does the adoption of XVIF entail modifications to the schemas of the existing XML?

The framework is independent and can be used in addition to XML schemas. The same XML structures can be validated against additional XSEF rules without modifying the schemas.

Is there a way for XVIF to assist in the validation of non-XML data?

No, This framework is meant to verify document structure and expectation in XML content only. For other data formats other than XML, other technologies would be more appropriate.

Does XVIF interact with our XML editor/parser/database?

If there is an XVIF processor implementation for your environment, the same XSEF rules are portable across parsers, editors, and other XML processing tools.