Elsevier

Computer Standards & Interfaces

Volume 50, February 2017, Pages 236-250
Computer Standards & Interfaces

Model transformation between OPC UA and UML

https://doi.org/10.1016/j.csi.2016.09.004Get rights and content

Highlights

  • OPC UA and UML are analyzed for correspondence.

  • Mappings are established between OPC UA elements and UML elements.

  • Based on the mappings, transformation rules are defined in QVT.

  • Three case examples are presented demonstrating transformation.

Abstract

OPC Unified Architecture (UA) is a platform-independent standard for message-based communication between clients and servers on various types of network to facilitate information exchange. OPC UA has been adopted in various domains such as power grids, building automation, and smart devices to support interoperability of involved systems. These domains also use Unified Modeling Language (UML) as the standard notation for data modeling or system modeling. Use of two different notations in the same domain causes compatibility issues. To address this, we present an approach for transforming OPC UA to UML to improve their compatibility and integration. In the approach, we rigorously analyze the semantics of OPC UA elements and establish a mapping between OPC UA elements and UML elements based on the analysis. Based on the mapping, we define transformation algorithms using Query/View/Transformation (QVT) which is a standard model transformation language by OMG. We demonstrate the approach using case examples in the power grid, building automation, and smart device domains.

Introduction

OPC Unified Architecture (OPC UA) [1] is a standard for information exchange for industrial systems (e.g., manufacturing systems) and it has been adopted in various domains such as power grids (e.g., [2], [3], [4]) building automation (e.g., [5], [6], [7]), and smart devices (e.g., [1], [8]) to address interoperability where it serves as a base for Seamless Integration Architecture [9]. Another standard that has been widely adopted in these domains (e.g., [10], [11], [12], [13], [14], [15]) is the Unified Modeling Language (UML) [16] which is the standard for modeling software systems. As witnessed above, the UML has rapidly expanded its applicability to the major domains at which OPC UA aims and there has been an increasing overlap of the two standards in their coverage and use. However, the two standards OPC UA and UML have different notations which have caused confusion in understanding their notations.

To the best of our knowledge, there is no existing work addressing the transformation of UML to OPC UA. The most relevant work is mapping IEC 61850 and CIM (which are the standard data models described in UML in the power domain) to OPC UA (e.g., [2], [3], [17]). In their work, one mapping is defined between IEC 61850 elements and OPC UA elements and another mapping is defined between CIM elements and OPC UA elements. Based on the mappings, they generate corresponding XML expressions describing OPC UA elements. Although IEC 61850 and CIM are described in UML, their mappings are driven by the semantics of IEC 61850 and CIM. Thus, the existing work does not address general mappings independent from any specific domain between UML and OPC UA.

In this work, we present a metamodeling approach for transforming OPC UA model instances to UML models. Specifically, we focus on OPC UA AddressSpace Model [1] which defines objects and related information provided by servers to clients. The corresponding part in UML is the Common Structure, Values, Classification, Simple Classifier, and Structured Classifier models [16] which define structural aspects of UML. Thus, we focus on these models. Within the scope, we analyze the semantics of involved OPC UA and UML elements and establish mappings between them with rigorous rationales. Based on the mapping, we define transformation algorithms using Query/View/Transformation (QVT) [18], a de facto standard for model transformation by Object Management Group (OMG). We demonstrate transformation through three case examples, the first one in the power grid domain, the second one in the building automation domain, and the third one in the smart device domain. The first and second examples demonstrate the transformation from OPC UA to UML, while the third one shows the opposite from UML to OPC UA. Major contributions of this work include the definition of a general mapping between OPC UA and UML which can be used across different domains, rigorous reasonings about mapping definitions based on a semantic analysis of involved elements, use of the standard transformation language QVT for describing transformation algorithms, and support for bi-directional transformation.

The rest of the paper is organized as follows. Section 2 gives an overview of OPC UA and UML. Section 3 analyzes the semantics of OPC UA and UML elements and defines mappings between them. Section 4 describes QVT transformation algorithms for bi-direction transformation from OPC UA to UML and vice versa. Section 5 demonstrates the three case examples in the power grid, building automation, and smart device domains. Section 6 discusses related work. Section 7 concludes the paper.

Section snippets

Background

In this section, we give an overview of UML and OPC UA in terms of metamodels and model elements.

Mapping UML to OPC UA

In this section, we analyze the correspondence between OPC UA elements and UML elements in terms of data entities, relationships, and data types. The analysis focuses on the Address Space model in OPC UA and its corresponding part the Classification model in UML.

QVT transformation

In this section, we describe model transformation between OPC UA models and UML models using QVT. We considered QVT [18] and ATL [20] and chose QVT as the base transformation platform because it is a standard for transforming models by OMG which also defines the UML. Thus, QVT has better compatibility with the UML. Also, QVT have been more widely adopted. In the power domain, QVT has also been adopted by IEC 62361 [21], which has been drafted by WG19, for specifying mappings between IEC 61850

Case studies

In this section, we present three case studies of transforming an OPC UA model to a UML model or vice versa based on the mapping defined in Section 3 and the transformation rules in Section 4. In the first case study, we demonstrate the transformation of an OPC UA model to a UML model in the power grid domain. The second case study demonstrates the transformation of an OPC UA model to a UML in the building automation domain. Lastly, the third case study presents the opposite transformation from

Related work

In this section, we review existing works (e.g., [2], [3], [4] which are all from the same research group) on mapping IEC 61850 and CIM to OPC UA. IEC 61850 and CIM are the data model standards in the power system domain which are described in UML (with certain variations in IEC 61850). As they are described in UML, the existing work can be viewed as relevant to mapping UML (in the context of the power domain) to OPC UA. Their work can be divided into mapping IEC 61850 to OPC UA and mapping CIM

Conclusion

We have presented an approach for bi-directional transformation between OPC UA and UML. In the approach, we analyzed the semantics of OPC UA elements and mapped them to corresponding UML elements. Based on the mapping, we defined transformation algorithms described in QVT. We demonstrated the approach using three case examples in the power grid, building automation, and smart device domains. A major contribution of this work is that the defined mapping for transformation is general enough to be

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