AAS JSON: Introducing ModelVersion For Enhanced Interoperability

by Omar Yusuf 65 views

Hey guys! Today, we're diving deep into a crucial update for Asset Administration Shell (AAS) JSON objects: the introduction of modelVersion. This might sound a bit technical, but trust me, it's a game-changer for ensuring smooth interoperability and reducing potential errors. Let's break it down!

The Problem: Deserializing AAS JSON Objects Without Version Knowledge

So, what's the big deal? Well, when you're dealing with AAS JSON objects, you need to know which AAS version was used to create them. Without this knowledge, deserializing these objects becomes a real headache. Think of it like trying to read a book written in a language you don't fully understand – you might get some of it, but you're likely to miss crucial details.

The current situation is that a deserializer (a tool that converts JSON into a usable object) has no way to figure out the correct AAS version just by looking at the JSON itself. Unlike XML, which uses namespaces to provide version information, JSON lacks this built-in mechanism. This implicit knowledge requirement is where things get tricky and can lead to errors. This is a critical issue because the promise of AAS is seamless interoperability, and version ambiguity directly undermines that promise.

Why Implicit Knowledge is a Problem

The reliance on implicit knowledge of the AAS version is error-prone. Imagine a scenario where different systems are using different versions of AAS. If a system tries to process a JSON object created with a newer version using an older version's deserializer, things can go south quickly. Fields might be misinterpreted, data might be lost, or the entire process might fail. This lack of clarity directly impacts the reliability and consistency of data exchange, which is a cornerstone of the AAS concept.

Another key issue is that it harms the interoperability promise of AAS. The whole point of AAS is to create a standardized way to represent assets and their information, allowing different systems and organizations to communicate seamlessly. If versioning isn't handled explicitly, it creates a significant barrier to interoperability. Systems might struggle to understand each other's data, leading to integration challenges and hindering the widespread adoption of AAS.

The Solution: Adding modelVersion Attribute

Now, let's talk about the fix! The proposed solution is to add modelVersion as an optional attribute to key AAS components like Asset Administration Shells, Submodels, and Concept Descriptions. This attribute would clearly state the version of the AAS metamodel used to create the object. Think of it as a version tag right on the JSON object itself. This is a simple yet powerful solution that brings clarity and reduces ambiguity.

The value range for modelVersion would follow the semantic versioning pattern (e.g., "3.0.0" or "3.1.0"). This means we'd have a clear way to distinguish between major, minor, and patch versions, allowing deserializers to handle different versions gracefully. We can even discuss whether to include the patch/bugfix position in the version string, giving us even finer-grained control over version compatibility. Semantic versioning ensures that changes are communicated clearly and that systems can react appropriately.

Where to Add modelVersion

This modelVersion attribute needs to be added to several core AAS classes to be truly effective. We're talking about:

  • Asset Administration Shells: The top-level container for all asset information.
  • Submodels: Represent specific aspects or views of an asset.
  • Concept Descriptions: Provide semantic definitions for properties and other elements.

But it doesn't stop there! This change also needs to be reflected in the API-only classes, such as AssetAdministrationShellDescriptor. These descriptors are used for exchanging metadata about AAS, so including the modelVersion here is crucial for ensuring consistent interpretation of the metadata.

Benefits of modelVersion

Adding the modelVersion attribute brings a host of benefits:

  • Clear Version Identification: No more guessing games! Deserializers can easily determine the AAS version by inspecting the modelVersion attribute.
  • Improved Interoperability: Systems can confidently process JSON objects created with different AAS versions, knowing exactly how to interpret the data.
  • Reduced Errors: Explicit versioning minimizes the risk of misinterpretation and data loss during deserialization.
  • Future-Proofing: As AAS evolves, modelVersion will ensure that older objects can still be processed correctly, and newer objects can take advantage of new features without breaking compatibility.

Alternatives Considered: The Implicit Knowledge Approach (and Why It Falls Short)

Before settling on the modelVersion solution, the team considered sticking with the current approach: relying on implicit knowledge of the AAS version. However, as we've already discussed, this approach has some serious drawbacks.

The main issue is that it's simply not reliable. Implicit knowledge is prone to human error, miscommunication, and outdated assumptions. It also makes it difficult to maintain a clear understanding of which versions are compatible with which systems. In a complex ecosystem with multiple stakeholders, relying on implicit knowledge is a recipe for disaster.

By contrast, the modelVersion attribute provides a concrete, machine-readable way to identify the AAS version. This makes it much easier to automate version handling and ensure consistency across different systems. This proactive approach significantly reduces the risk of errors and promotes smoother interoperability.

Additional Context and Next Steps

This proposal to add modelVersion is a direct response to the challenges of deserializing AAS JSON objects without explicit version information. It's a crucial step towards fulfilling the AAS promise of seamless interoperability and reducing the risk of errors. This is a collaborative effort, and community feedback is essential to ensure the best possible implementation.

The next steps involve further discussion within the AAS community, refining the specifics of the modelVersion implementation, and incorporating the changes into the AAS specification. We'll also need to update existing libraries and tools to support the new attribute. The goal is to make this transition as smooth and painless as possible for everyone involved.

Semantic Versioning: A Quick Primer

Since we're talking about modelVersion and its value range following semantic versioning, let's take a quick detour to understand what semantic versioning is all about. Semantic versioning is a widely adopted versioning scheme that uses a three-part number: MAJOR.MINOR.PATCH (e.g., 3.1.0). Each part has a specific meaning:

  • MAJOR: Incremented when you make incompatible API changes. This indicates a significant overhaul that might break existing integrations.
  • MINOR: Incremented when you add functionality in a backwards-compatible manner. This means new features are added without disrupting existing code.
  • PATCH: Incremented when you make backwards-compatible bug fixes. These are typically small, non-breaking changes to address issues.

By adhering to semantic versioning, we can clearly communicate the nature of changes in AAS and help users understand the potential impact of upgrading to a new version. This clear communication is essential for maintaining a healthy ecosystem and ensuring smooth transitions between versions.

Applying Semantic Versioning to modelVersion

When we apply semantic versioning to the modelVersion attribute, it gives us a powerful tool for managing compatibility. For example:

  • If a deserializer encounters a JSON object with a major version higher than it supports, it knows that there might be incompatible changes and can take appropriate action (e.g., throw an error or attempt a graceful fallback).
  • If the minor version is higher, the deserializer knows that new features might be present but that the core structure should still be compatible.
  • If only the patch version is different, the deserializer can be confident that it's dealing with bug fixes and that the object should be fully compatible.

By leveraging semantic versioning, we can build robust and resilient systems that can adapt to changes in AAS over time. This adaptability is crucial for the long-term success of AAS and its widespread adoption.

Implementing modelVersion in API-Only Classes

As mentioned earlier, it's vital to include the modelVersion attribute not only in the core AAS classes but also in the API-only classes like AssetAdministrationShellDescriptor. These descriptors play a crucial role in exchanging metadata about AAS, and including version information here is essential for ensuring consistent interpretation.

Think of it this way: the descriptor is like a summary of the AAS, providing key information about its structure and content. If the descriptor doesn't include the modelVersion, then the recipient might misinterpret the data and make incorrect assumptions about the AAS. This consistency ensures that metadata exchange is reliable and accurate.

Benefits of modelVersion in Descriptors

Adding modelVersion to descriptors brings several advantages:

  • Accurate Metadata Interpretation: Recipients can accurately determine the AAS version based on the descriptor, preventing misinterpretations.
  • Consistent Communication: Ensures that metadata exchange is consistent across different systems and organizations.
  • Simplified Integration: Makes it easier to integrate AAS data into various applications and platforms.

By including modelVersion in descriptors, we create a more robust and reliable ecosystem for AAS metadata exchange. This holistic approach ensures that versioning is handled consistently across all aspects of AAS.

Conclusion: Embracing Explicit Versioning for a Stronger AAS Ecosystem

In conclusion, the introduction of the modelVersion attribute for JSON objects in AAS is a significant step forward. By moving away from implicit knowledge and embracing explicit versioning, we're building a stronger, more reliable, and more interoperable AAS ecosystem. This proactive measure reduces the risk of errors, simplifies integration, and ensures that AAS can evolve gracefully over time.

This change will benefit everyone involved in the AAS community, from developers building AAS-based systems to organizations exchanging asset information. By working together to implement modelVersion effectively, we can unlock the full potential of AAS and create a truly interconnected world of industrial assets. This collaborative effort will pave the way for a future where data exchange is seamless, reliable, and secure.

So, what are your thoughts on the modelVersion proposal? Let's continue the discussion and work together to make AAS the best it can be! Your feedback matters, and your contributions are essential to the success of AAS.