After more than thirty-five years of research and development in software architecture, several fundamental challenges remain unsolved. First, despite the importance of having a well-defined architecture description aligned with the system, inconsistencies and misalignments are still prevalent. Second, although numerous languages exist to describe architectures, none have achieved widespread use or recognition as a de facto standard. Third, while architecture is dynamic and evolving, with architectural decisions often made by non-architect stakeholders, there are no universally accepted methodologies to capture emergent aspects and incorporate them into the architecture.In this paper, we explore the emerging concept of architecture as code. Inspired by the success of infrastructure as code, which enables infrastructure management in a codified, automated, and repeatable manner, architecture as code aims to bring similar benefits to software architecture. To the best of our knowledge, this is the first scientific paper to study this concept in depth within the context of software architecture, providing a comprehensive description and analysis of its characteristics. We also investigate how architecture as code is implemented and applied in practice.

Digital twins, as virtual models reflecting physical entities, serve multiple purposes, supporting the understanding, design, and management of systems, across various domains. The concept of digital twins has been also applied to smart cities, coining the term “Urban Digital Twin”. Indeed, smart cities continuously produce data that can serve as a real-time feed for their digital twin representations. However, developing urban digital twins is challenging as the domain is complex and evolving rapidly. Moreover, existing digital twin platforms are mostly generic platforms, limiting their adoption for a specific context such as smart cities. The aim of this study is to overcome the limitation of existing general-purpose digital twin platforms, particularly in the context of smart cities, by supporting the development and evolution of urban digital twins. To this aim, we propose a low-code assessment platform for smart cities represented as urban digital twins by leveraging distributed runtime models to implement and deploy service-based quality evaluation systems. The innovative platform and its architecture enable the creation of efficient urban digital twins, allowing for their continuous evolution without requiring redeployment whenever the digital twin definitions are modified. Experimental evaluations demonstrate the effectiveness and efficiency of the proposed platform, highlighting its potential for evolving urban digital twins in smart cities quality assessment. Results show evidence that combining distributed runtime models with the advantages of low-code platforms is beneficial within the smart cities domain. Moreover, this study underscores the significance of specialized platforms tailored to the smart cities domain.

Littering is a major problem that threatens the environment, society, and economy. Keep track, monitor and regularly clean littering sites can be a crucial problem that involves public authorities, municipalities, companies, and citizens. So far approaches have not well leveraged the knowledge and capabilities that derive from the federation of multiple communities, such as cities, public bodies, and organizations. In this paper, we describe the COBOL project, a National PRIN (Progetti di Rilevante Interesse Nazionale) PNRR (Piano Nazionale Ripresa e Resilienza) project funded by the Italian MUR (Ministero dell'Università e della Ricerca) in 2023. The project aims to definite a flexible framework for managing the waste disposal process through a federated learning architecture that collects and integrates the reports (e.g., annotated pictures and user feedback) shared by the communities involved in the waste disposal process. To deliver an advanced waste disposal service based on the direct participation of citizens, COBOL also integrates Model-Driven Engineering principles, Computer Vision techniques, and Self-Adaptation mechanisms. Early results show that reports can be effectively collected and processed with COBOL.

Travel Recommender Systems (TRSs) have been proposed to ease the burden of choice in the travel domain, by providing valuable suggestions based on user preferences. Despite the broad similarities in functionalities and data provided by TRSs, these systems are significantly influenced by the diverse and heterogeneous contexts in which they operate. This plays a crucial role in determining the accuracy and appropriateness of the travel recommendations they deliver. For instance, in contexts like smart cities and natural parks, diverse runtime information-such as traffic conditions and trail status, respectively-should be utilized to ensure the delivery of pertinent recommendations, aligned with user preferences within the specific context. However, there is a trend to build TRSs from scratch for different contexts, rather than supporting developers with configuration approaches that promote reuse, minimize errors, and accelerate time-to-market. To illustrate this gap, in this paper, we conduct a systematic mapping study to examine the extent to which existing TRSs are configurable for different contexts. The conducted analysis reveals the lack of configuration support assisting TRSs providers in developing TRSs closely tied to their operational context. Our findings shed light on uncovered challenges in the domain, thus fostering future research focused on providing new methodologies enabling providers to handle TRSs configurations.

Robotic Process Automation (RPA) uses automation technologies to imitate business tasks performed by humans. Digital Automation Platforms are extremely useful services that enable developers to connect applications and automate work-flows and Workflow Automation Tools (WATs) offer tremendous advantages in orchestrating tasks and services. Even if the workflow composition in WATs is offered in a low-code fashion, the unsupervised and autonomous execution of the tasks and transactions between various software systems are performed even if they are completely unrelated. For this reason, building workflows and optimizing them can be a difficult and time-consuming task. Since the workflow orchestrates external systems, we cannot assure that the execution will not fail, or that unexpected problems will arise during the evolution of the orchestrated systems. In this paper, we investigate these challenges and open issues related to unsupervised workflow declarations, and we envisage a general approach to assist the workflow definition.

Software architectures are pivotal in the success of software-intensive systems and serve as foundational elements that significantly impact the overall software quality. Reference architectures abstract software elements, define main responsibilities and interactions within a domain, and guide the architectural design of new systems. Using reference architectures offers advantages like enhanced interoperability, cost reduction through reusability, decreased project risks, improved communication, and adherence to best practices. However, these benefits are most pronounced when software architectures align with reference architectures. Deviations from prescribed reference architectures can nullify these benefits. Uncontrolled misalignment can become prohibitively expensive, necessitating costly redevelopments, with maintenance costs reaching up to 90% of development costs. Conformance-checking processes and identifying and resolving violations in the software architecture are essential to mitigate misalignment. To address these challenges, we introduce the concept of continuous conformance that is expressed as a distance function, together with a process supporting it. Continuous conformance quantifies the degree to which a software architecture adheres to a designated reference architecture. The conformance concept enables multi-level, incremental, and non-blocking checking and restoration tasks and allows the check of partial architectures without obstructing the design process. We operationalize this process through an assistive modeling tool to architect an Internet of things-based system.

Model-Driven Engineering (MDE) is a software engineering methodology focusing on models as primary artifacts. In the last years, the emergence of Web technologies has led to the development of Web-based modeling tools and model-based approaches for the Web that offer a web-based environment to create and edit models or model-based low-code solutions. A common requirement when developing Web-based modeling tools is to provide a fast and efficient way for model management, and this is particularly a hot topic in model-based system engineering. However, the number of approaches offering RESTful services for model management is still limited. Among the alternatives for developing distributed services, there is a growing interest in the use of RESTful services. In this paper, we present an approach to provide RESTful services for model management that can be used to interact with any kind of model, and can be used to build a modeling platform providing modeling-as-a-service. The approach follows the REST principles to provide a stateless and scalable service.

The increasing complexity of modern systems leads to an increasing amount of artifacts that are used along the model-based software and systems development lifecycle. This also includes model transformations, which serve for mapping models between representations, e.g., for verification and validation purposes. Model repositories manage this variety of artifacts and promote reusability, but should also enable the bundling of compatible artifacts. Therefore, model transformations should be reused and arranged into transformation chains to support more complex transformation scenarios. The resulting transformation should correspond to the user’s interest in terms of quality criteria such as model coverage, transformation coverage, and number of transformation steps, thus assembling such chains becomes a multi-objective problem. A novel multi-objective approach for exploring possible transformation chains residing in model repositories is presented. MOMoT, a model-driven optimization framework, is leveraged to explore the transformation space spanned by the repository. For demonstration, three differently populated repositories are considered. We have extended MOMoT with an exhaustive, multi-objective search that explores the entire model transformation space defined by graph transformation rules, allowing all possible transformation chains to be considered as solution. Accordingly, the optimal solutions were identified in the demonstration cases with negligible computation time. The approach assists modelers when there are multiple chains for transforming an input model to a specified output model to consider. Our evaluation shows that the approach elicits all legitimate transformation chains, thus enabling the modelers to consider trade-offs in view of multiple criteria selection.

In Model-Driven Engineering, metamodels define the vocabulary of concepts and relations that designers use to define a wide range of artifacts, including models, transformations, and editors. Therefore, whenever a metamodel undergoes modifications, the depending artifacts may no longer be valid, and consistency needs to be repaired through coupled evolution techniques. While several approaches have been proposed over the last decades, they are artifact- and domain-specific and do not facilitate the reuse of migration strategies. Indeed, migration strategies are often hard-coded for a given project in a specific domain. In this paper, we propose the novel concept of migration patterns to leverage reuse across different domains and projects. The approach extends the existing Edelta framework and has been evaluated by considering several case studies identified in a systematic literature review.

Summary Models are core assets in Model‐Driven Engineering (MDE). They are pervasively used throughout software development processes to leverage automation, increase cost‐effectiveness, and enhance quality factors. Model repositories have been successfully proposed to enforce reuse and elicit correlations among modeling artifacts, enabling storing operations on model‐based artifacts and collaborative modeling features. Maintaining and improving the quality of modeling artifacts is mandatory for software quality scale‐ups. Limiting the exploration of datasets and repositories of models to individual artifacts might reduce the ability to capture insights and reuse opportunities. This paper proposes AMINO, an analytics tool for model repositories supporting the discovery and quality evaluation of modeling ecosystems.

The importance of software architecture is largely recognized also in iterative and agile development settings. However, it is quite complex to provide evidence that an architecture is of good quality and that the architectural decisions are appropriate, correct, or optimal. Architecture evaluation aims at showing and providing confidence that design decisions contribute to fulfilling the stakeholder concerns. Some architecture evaluation methods are scenario-based and aim at balancing many potentially conflicting quality attributes. Other works focus on a specific quality attribute and provide metrics to measure it.In this paper we survey the state of the art in metrics for evaluating quality attributes of architectures. The elicited metrics are organized into a catalog, which associates them with the specific quality attributes they aim to measure. We contribute also an MDE framework that generates web views facilitating the analysis of architectures. In this way, researchers and practitioners can easily retrieve the metrics that are appropriate to their specific needs. The catalog of metrics and quality attributes is released to the research community and open to contributions from experts and practitioners.

Abstract Reference architectures (RAs) are successfully used to represent families of concrete software architectures in several domains such as automotive, banking, and the Internet of Things. RAs inspire architects when designing concrete architectures, and they help to guarantee compliance with architectural decisions, regulatory requirements, as well as architectural qualities. Despite their importance, reference architectures still suffer from a number of open technical issues, including (i) the lack of a common interpretation, a precise notation for their representation and documentation, and (ii) the lack of conformance mechanisms for checking the compliance of concrete architectures to their related reference architecture, architectural decisions, regulatory requirements, etc. This paper addresses these two issues by introducing a model-driven approach that leverages (i) a domain-independent metamodel for the representation of reference architectures and (ii) the combination of model transformation and weaving techniques for the automatic conformance checking of concrete architectures. We evaluate the applicability, effectiveness, and generalizability of our approach using illustrative examples from the web browsers and automotive domains, including an assessment from an independent practitioner.

Abstract Low‐code development platforms (LCDPs) aim to simplify software systems' development by providing easy‐to‐use graphical interfaces and drag‐and‐drop facilities. The system behaviors are defined through available data handling and workflow mechanisms enabling the specification of business processes from users that do not have strong programming skills. However, the number of LCDPs has grown significantly over the last few years. Consequently, it is not easy for inexpert users to understand their differences, especially in terms of provided modeling constructs. In this article, we analyze and compare eight low‐code development platforms by focusing on their capabilities for specifying business processes. The analysis exploits business process modeling and notation (BPMN) as a reference modeling language. Thus, the core elements of BPMN are leveraged to analyze the workflow mechanisms provided by each of the analyzed LCDP. The article explains different types of process flows and data handling means of the different LCDPs aiming to give potential users objective elements that can be used to make educated decisions when selecting LCDPs.

In the model-driven security domain, access control systems provide an application for handling access of persons through controlled gates. A gate, such as a door, can have a lock mechanism for securing the area from unauthorized access. Most commercial solutions for access control management offer pre-packaged software systems where customization of the authorization logic is either not allowed or subject to payment. Moreover, cross-platform development is a barrier for solution providers due to the high cost of development and maintenance that it implies. To overcome these limitations and further optimize the entire access control systems development process, we propose a model-driven approach that supports automatic code generation to enable communication between an IoT infrastructure and platforms for Facility Access Management. Specifically, the approach combines the benefits of Near-Field Communication (NFC) and Tinkerforge (i.e., an open-source hardware platform) with model-driven techniques. This allows the approach to exploit both behavioral and structural models for the modeling and the consequent code generation of part of the authorization mechanism, thus providing complete coverage of the code generated for the whole system. We implemented and evaluated our approach in a real-world case study within the premises of a fitness center with an IoT infrastructure consisting of several heterogeneous sensors by showing its practical applicability. Experimental results demonstrate the effectiveness of our approach in supporting abstraction and automation concerning traditional code-centric development through code generation features. Consequently, our approach makes the whole development process less time-consuming and error-prone, thus reducing the system's time to market.

Multimodal journey planners are used worldwide to support travelers in planning and executing their journeys. Generated travel plans usually involve local mobility service providers, consider some travelers’ preferences, and provide travelers information about the routes’ current status and expected delays. However, those planners cannot fully consider the special situations of individual cities when providing travel planning services. Specifically, authorities of different cities might define customizable regulations or constraints of movements in the cities (e.g., due to construction works or pandemics). Moreover, with the transformation of traditional cities into smart cities, travel planners could leverage advanced monitoring features. Finally, most planners do not consider relevant information impacting travel plans, for instance, information that might be provided by travelers (e.g., a crowded square) or by mobility service providers (e.g., changing the timetable of a bus). To address the aforementioned shortcomings, in this paper, we propose ROUTE, a framework for customizable smart mobility planners that better serve the needs of travelers, local authorities, and mobility service providers in the dynamic ecosystem of smart cities. ROUTE is composed of an architecture, a process, and a prototype developed to validate the feasibility of the framework. Experiments’ results show that the framework scales well in both centralized and distributed deployment settings.

Abstract In model-driven software engineering, models are used in all phases of the development process. These models must hold a high quality since the implementation of the systems they represent relies on them. Several existing tools reduce the burden of manually dealing with issues that affect models’ quality, such as syntax errors, model smells, and inadequate structures. However, these tools are often inflexible for customization and hard to extend. This paper presents a customizable and extensible model repair framework, PARMOREL, that enables users to deal with different issues in different types of models. The framework uses reinforcement learning to automatically find the best sequence of actions for repairing a broken model according to user preferences. As proof of concept, we repair syntactic errors in class diagrams taking into account a model distance metric and quality characteristics. In addition, we restore inter-model consistency between UML class and sequence diagrams while improving the coupling qualities of the sequence diagrams. Furthermore, we evaluate the approach on a large publicly available dataset and a set of real-world inspired models to show that PARMOREL can decide and pick the best solution to solve the issues present in the models to satisfy user preferences.

Abstract Like any software artifacts, metamodels are evolving entities that constantly change over time for different reasons. Changing metamodels by keeping them consistent with other existing artifacts is an error-prone and tedious activity without the availability of automated support. In this paper, we foster the adoption of metamodel refactorings collected in a curated catalog. The Edelta framework is proposed as an operative environment to provide modelers with constructs for specifying basic refactorings and evolution operators, to define a complete metamodel refactoring catalog. The proposed environment has been used to implement the metamodel refactorings available in the literature and make them executable. A detailed discussion on how modelers can use and contribute to the definition of the catalog is also given.

Abstract Smart decision making plays a central role for smart city governance. It exploits data analytics approaches applied to collected data, for supporting smart cities stakeholders in understanding and effectively managing a smart city. Smart governance is performed through the management of key performance indicators (KPIs), reflecting the degree of smartness and sustainability of smart cities. Even though KPIs are gaining relevance, e.g., at European level, the existing tools for their calculation are still limited. They mainly consist in dashboards and online spreadsheets that are rigid, thus making the KPIs evolution and customization a tedious and error-prone process. In this paper, we exploit model-driven engineering (MDE) techniques, through metamodel-based domain-specific languages (DSLs), to build a framework calledMIKADO for the automatic assessment of KPIs over smart cities. In particular, the approach provides support for both: (i) domain experts, by the definition of a textual DSL for an intuitive KPIs modeling process and (ii) smart cities stakeholders, by the definition of graphical editors for smart cities modeling. Moreover, dynamic dashboards are generated to support an intuitive visualization and interpretation of the KPIs assessed by our KPIs evaluation engine. We provide evaluation results by showing a demonstration case as well as studying the scalability of the KPIs evaluation engine and the general usability of the approach with encouraging results. Moreover, the approach is open and extensible to further manage comparison among smart cities, simulations, and KPIs interrelations.

Abstract Metamodels play a crucial role in any model-based application. They underpin the definition of models and tools, and the development of model management operations, including model transformations and analysis. Like any software artifacts, metamodels are subject to evolution to improve their quality or implement unforeseen requirements. Metamodels can be defined in terms of existing ones to increase the separation of concerns and foster reuse. However, the induced coupling can give additional evolution complexity, and dedicated support is needed to avoid breaking metamodels defined in terms of those being changed. This paper presents a tool-supported approach that can automatically analyze the available metamodels and alert modelers in case of change operations that can give place to invalid situations like dangling references. The approach has been implemented in the Edelta development environment and successfully applied to metamodels retrieved from a publicly available Ecore models dataset.

Over the last decade, several repositories have been proposed by the Model-Driven Engineering (MDE) community to enable the reuse of modeling artifacts and foster empirical studies to analyze specifications and tools made available by MDE researchers and practitioners. In this respect, different approaches have been proposed to measure the quality of, e.g., models, metamodels, and transformations, with respect to characteristics defined by quality models. However, when a modeling ecosystem is available, measuring the constituting artifacts singularly might not be enough. This paper proposes a quality assessment approach, which considers the relationships among the artifacts under analysis as part of the quality measurement process. For instance, to assess the quality of model transformations, further than measuring their structural characteristics, users might be interested in quality aspects like coverage and information loss related to the depending metamodels and the way models are consumed by transformations, respectively. The proposed approach is based on weaving models, which permit to link quality definitions of different kinds of artifacts, and it can generate Epsilon Object Language (EOL) programs by means of a model-to-code transformation to perform the specified quality assessment process.

Abstract Modeling is a ubiquitous activity in the process of software development. In recent years, such an activity has reached a high degree of intricacy, guided by the heterogeneity of the components, data sources, and tasks. The democratized use of models has led to the necessity for suitable machinery for mining modeling repositories. Among others, the classification of metamodels into independent categories facilitates personalized searches by boosting the visibility of metamodels. Nevertheless, the manual classification of metamodels is not only a tedious but also an error-prone task. According to our observation, misclassification is the norm which leads to a reduction in reachability as well as reusability of metamodels. Handling such complexity requires suitable tooling to leverage raw data into practical knowledge that can help modelers with their daily tasks. In our previous work, we proposed AURORA as a machine learning classifier for metamodel repositories. In this paper, we present a thorough evaluation of the system by taking into consideration different settings as well as evaluation metrics. More importantly, we improve the original AURORA tool by changing its internal design. Experimental results demonstrate that the proposed amendment is beneficial to the classification of metamodels. We also compared our approach with two baseline algorithms, namely gradient boosted decision tree and support vector machines. Eventually, we see that AURORA outperforms the baselines with respect to various quality metrics.

Studies on public transportation in Europe suggest that European inhabitants use buses in ca. 56% of all public transport travels. One of the critical factors affecting such a percentage and more, in general, the demand for public transport services, with an increasing reluctance to use them, is their quality. End-users can perceive quality from various perspectives, including the availability of information, i.e., the access to details about the transit and the provided services. The approach proposed in this paper, using innovative methodologies resorting on data mining and machine learning techniques, aims to make available the unavailable data about public transport. In particular, by mining GPS traces, we manage to reconstruct the complete transit graph of public transport. The approach has been successfully validated on a real dataset collected from the local bus system of the city of L'Aquila (Italy). The experimental results demonstrate that the proposed approach and implemented framework are both effective and efficient, thus being ready for deployment.

In model-driven software engineering, models are used in all phases of the development process. These models may get broken due to various editions during the modeling process. There are a number of existing tools that reduce the burden of manually dealing with correctness issues in models, however, most of these tools do not prioritize customization to follow user requirements nor allow the extension of their components to adapt to different model types. In this paper, we present an extensible model repair framework which enables users to deal with different types of models and to add their own repair preferences to customize the results. The framework uses customizable learning algorithms to automatically find the best sequence of actions for repairing a broken model according to the user preferences. As an example, we customize the framework by including as a preference a model distance metric, which allows the user to choose a more or less conservative repair. Then, we evaluate how this preference extension affects the results of the repair by comparing different distance metric calculations. Our experiment proves that extending the framework makes it more precise and produces models with better quality characteristics.

Conventional wisdom on model transformations in Model-Driven Engineering (MDE) suggests that they are crucial components in modeling environments to achieve superior automation, whether it be refactoring, simulation, or code generation. While their relevance is well-accepted, model transformations are challenging to design, implement, and verify because of the inherent complexity that they must encode. Thus, defining transformations by chaining existing ones is key to success for enhancing their reusability. This paper proposes an approach, based on well-established algorithms, to support modellers when multiple transformation chains are available to bridge a source metamodel with a target one. The all-important goal of selecting the optimal chain has been based on the quality criteria of coverage and information loss. The feasibility of the approach has been demonstrated by means of experiments operated on chains obtained from transformations borrowed from a publicly available repository.

Metamodels are at the core of any modeling ecosystem. As their evolution is inevitable, the management of artifacts which depend on these metamodels is a complicated task. Restoring the validity of the corrupted artifacts after a metamodel evolution in a (semi-)automated manner is intrinsically difficult especially when considering the exact impact of the evolution on the restoring process. In this paper, we propose a generic approach to automatically quantify and identify the impact of metamodel evolution on two related artifacts: models and transformations. The approach starts from the evolution definition and generates OCL queries that can be executed on these artifacts to obtain the impacted elements. The knowledge gained from the impact analysis may then guide the user in the decision on whether to proceed with the evolution or to revert it.

Manual classification methods of metamodel repositories require highly trained personnel and the results are usually influenced by the subjectivity of human perception. Therefore, automated metamodel classification is very desirable and stringent. In this work, Machine Learning techniques have been employed for metamodel automated classification. In particular, a tool implementing a feed-forward neural network is introduced to classify metamodels. An experimental evaluation over a dataset of 555 metamodels demonstrates that the technique permits to learn from manually classified data and effectively categorize incoming unlabeled data with a considerably high prediction rate: the best performance comprehends 95.40% as success rate, 0.945 as precision, 0.938 as recall, and 0.942 as F1 score.

Model transformations are key elements of model-driven engineering, where they are used to automate the manipulation of models. However, they are typed with respect to concrete source and target meta-models, making their reuse for other (even similar) meta-models challenging. To improve this situation, we propose capturing the typing requirements for reusing a transformation with other meta-models by the notion of a typing requirements model (TRM). A TRM describes the prerequisites that a model transformation imposes on the source and target meta-models to obtain a correct typing. The key observation is that any meta-model pair that satisfies the TRM is a valid reuse context for the transformation at hand. A TRM is made of two domain requirement models (DRMs) describing the requirements for the source and target meta-models, and a compatibility model expressing dependencies between them. We define a notion of refinement between DRMs and see meta-models as a special case of DRM. We provide a catalogue of valid refinements and describe how to automatically extract a TRM from an ATL transformation. The approach is supported by our tool TOTEM. We report on two experiments—based on transformations developed by third parties and meta-model mutation techniques—validating the correctness and completeness of our TRM extraction procedure and confirming the power of TRMs to encode variability and support flexible reuse.

Model transformations are considered to be the "heart" and "soul" of Model Driven Engineering, and as a such, advanced techniques and tools are needed for supporting the development, quality assurance, maintenance, and evolution of model transformations. Even though model transformation developers are gaining the availability of powerful languages and tools for developing, and testing model transformations, very few techniques are available to support the understanding of transformation characteristics. In this paper, we propose a process to analyze model transformations with the aim of identifying to what extent their characteristics depend on the corresponding input and target met models. The process relies on a number of transformation and metamodel metrics that are calculated and properly correlated. The paper discusses the application of the approach on a corpus consisting of more than 90 ATL transformations and 70 corresponding metamodels.

In Model-Driven Engineering (MDE) metamodels play a key role since they underpin the specification of different kinds of modeling artifacts, and the development of a wide range of model management tools. Consequently, when a metamodel is changed modelers and developers have to deal with the induced coupled evolutions i.e., adapting all those artifacts that might have been affected by the operated metamodel changes. Over the last years, several approaches have been proposed to deal with the coupled evolution problem, even though the treatment of changes is still a time consuming and error-prone activity. In this paper we propose an approach supporting users during the adaptation steps that cannot be fully automated.~The approach has been implemented by extending the EMFMigrate language and by exploiting the user input facility of the Epsilon Object Language. The approach has been applied to cope with the coupled evolution of metamodels and model-to-text transformations

Metamodels are a key concept in Model-Driven Engineering. Any artifact in a modeling ecosystem has to be defined in accordance to a metamodel prescribing its main qualities. Hence, understanding common characteristics of metamodels, how they evolve over time, and what is the impact of metamodel changes throughout the modeling ecosystem is of great relevance. Similarly to software, metrics can be used to obtain objective, transparent, and reproducible measurements on metamodels too. In this paper, we present an approach to understand structural characteristics of metamodels. A number of metrics are used to quantify and measure metamodels and cross-link different aspects in order to provide additional information about how metamodel characteristics are related. The approach is applied on repositories consisting of more than 450 metamodels.