The ICT infrastructure of many manufacturing companies usually is composed of mixed or what is sometimes referred to as heterogeneous systems or platforms. This trend continues with the development of digital manufacturing platforms that are typically built around vendor specific technologies or closed standards. As each vendor or provider offers their platforms (often closed in nature for commercial and business reasons) the consumer is faced with an ever growing “collection” of solutions that may each address a specific part of the business needs. This raises interoperability issues particularly concerning cross platform connectivity and utilisation of software applications and data across multiple platforms.

The use of proprietary standards or even lack of transparency about standards, protocols and technologies used by the various platforms also raises the entry barriers or bars the integration of innovative solutions in existing platforms. In this respect, the challenge of interoperability across digital manufacturing platforms remains a key concern for not only manufacturers (as users and consumers) and software developers of smart factory solutions; but also for policy makers such as European Commission (EC) who have vested interest for businesses to take full advantage of interconnected systems in the manufacturing sector.

A study conducted by the DIGICOR project, of 10 research projects funded by EC under the Factories of Future public-private partnership, has resulted in the design of a Platform Interoperability framework. The framework is designed to gather insight from different digital manufacturing platforms and to highlight the potential for interconnection between the distributed platforms in a structured way.

The proposed Platform Interoperability Framework (illustrated below) takes into account the need for vertical digital manufacturing platforms to be communicable and interoperable.

The framework, although in its infancy, is domain agnostic in nature, Further development of the framework will focus on the granularity of information it can capture and represent as well as the support it can provide to platform interoperability initiatives e.g. in the form of recommendations or standardisation. In essence, the interoperability framework broadly promotes transparency along different levels of the platform. Particularly, it breaks down the interoperability issues faced in the Digital Manufacturing environment into a three tier hierarchy:

1. Platform: The first or bottom tier of the proposed Platform Interoperability Framework is concerned with Platform Management. It focuses on the separation of ‘identification’ from ‘services’ to allow Shared Access across different platforms. Steps taken and solutions implemented at this level should allow users to navigate through multiple platforms and identify points of interest. Approaches for single sign-on, policy based access and user right management can all contribute towards interoperability at this level..

2. Application: The second or middle hierarchal level of interoperability framework is Application Management. Once users have access to the platform, they know what is on offer, so the platform developers and providers should look at ways to allow users to use the application and services on offer, either locally or through remote access. This can be realised by supporting the uptake of modular applications development and packaging approaches that make it easier to port application across multiple platforms. With that, the idea is to support development of interoperable and reusable functionalities that can be ported and offered via different platforms.

3. Integration: The top level of interoperability framework is Integration, which can prove more complex than the previous levels owing to the complexity of dealing with heterogeneous standards, interfaces and communication protocols. Here the use of standards at all stages of the information/data flow can allow the applications, tools and services to be interoperable in an ecosystem environment.

In to evaluate the Platform Interoperability Framework, a qualitative study was conducted by the researchers from DIGICOR project. During the study, the interoperability framework was introduced to a number of EU funded research and innovation (Factories of Future) projects - all focusing on the development of smart factory platforms with multi-sided marketplaces. The projects were asked to provide two inputs:

• High-level mapping of the project or the platform with the three tiers of the proposed framework as an introduction to the platform

• Detailed mapping of project activities with the view to define use-cases or reference implementations of interoperable solution

The analysis of the information gathered through the Interoperability Framework highlighted several similarities in the use of technologies and standards among different projects. The analysis also helped identifying the use-case scenarios that that can be developed as reference implementations of interoperable solutions.

Some examples of the interoperability scenarios that emerged from the information gathered through the interoperability framework include:

1. Platform Level Interoperability Scenario: The analysis of the gathered information highlighted that the use of open standards for security and user authorisation such as OpenID Connect, OAuth 2.0 and SAML 2.0; and their implementation in open-source toolkits, such as Keycloak, is common across multiple projects. The use of common standards and open-source tools provides the platform developers or owners the opportunity to create federations or single sign-on solutions that contribute towards attracting more users to their platform.

2. Application Level Interoperability Scenario: The interoperability at application layer can be supported by the uptake of modular applications development and packaging approaches (e.g. Docker) that make it easier to port application across multiple platforms. With that the use or adoption of such technologies can support the development of reusable functionalities that can be ported and offered via different platforms. The information gathered through the interoperability framework showed that a number of ongoing projects are deploying their applications in containers or Cloud-based services. Thus a number of use-case scenarios can be drawn from the cross-platform applicability of applications and services developed in different projects.

3. Integration Level Interoperability Scenario: At the top level of interoperability framework, Integration can prove more complex than the other levels owning to the need for greater transparency both at platform and application ends. However, the integration of cross-platform applications can be facilitated through the use of open standards at both ends. For example, the information gathered through the interoperability framework shows that many ongoing EC projects are investigating middleware solutions to link data sources with applications. Here the use of standardised approaches (e.g. OPC-UA can allow developers to make their applications, tools and connectors to interconnect and communicate with the standard middleware.

The detailed results of the study are published in a paper titled "Towards Interoperability Across Digital Manufacturing Platforms" [1].

1. Usman Wajid, Gash Bhullar. Towards Interoperability Across Digital Manufacturing Platforms. In the proceedings of I-ESA2018 Interoperability for Enterprises and Applications conference. 2018