Environmental Modelling & Software 87 (2017) 49e63 Contents lists available at ScienceDirect Environmental Modelling & Software journal homepage: w ww.elsevier.com /locate/envsoft An overview of the model integration process: From pre-integration assessment to testing a, * a b Getachew F. Belete , Alexey Voinov , Gerard F. Laniak a University of Twente, ITC, 7500 AE Enschede, Netherlands b US Environmental Protection Agency, Office of Research and Development, USA a r t i c l e i n f o a b s t r a c t Article history: Integration of models requires linking models which can be developed using different tools, method- Received 15 March 2016 ologies, and assumptions. We performed a literature review with the aim of improving our under- Received in revised form standing of model integration process, and also presenting better strategies for building integrated 30 August 2016 modeling systems. We identified five different phases to characterize integration process: pre- Accepted 30 October 2016 integration assessment, preparation of models for integration, orchestration of models during simula- tion, data interoperability, and testing. Commonly, there is little reuse of existing frameworks beyond the development teams and not much sharing of science components across frameworks. We believe this Keywords: must change to enable researchers and assessors to form complex workflows that leverage the current Integrated modeling Interoperability environmental science available. In this paper, we characterize the model integration process and Interfaces compare integration practices of different groups. We highlight key strategies, features, standards, and Wrapping practices that can be employed by developers to increase reuse and interoperability of science software Components components and systems. Web services © 2016 Elsevier Ltd. All rights reserved. Contents 1. Introduction ...................................................................................................................................................................................................................................................... 50 2. Pre-integration assessment ............................................................................................................................................................................................................................. 51 3. Technical integration of models: preparing models for integration and orchestration of participating models during simulation ...................................... 53 3.1. Preparing models for integration ...................................................................................................................................................................................................... 53 3.2. Orchestration of participating models during simulation ............................................................................................................................................................ 54 3.3. Commonly used approaches for technical integration of models .............................................................................................................................................. 54 3.3.1. Component-based approach for technical integration of models ............................................................................................................................... 54 3.3.2. Web services and service-oriented approach for technical integration of models ................................................................................................. 55 3.3.3. Hybrid of component-based and web service-based approach for technical integration ................................................................................... 56 3.3.4. Tailor-made (custom-made) techniques for technical integration of models .......................................................................................................... 56 3.4. Interface standards and interoperability ......................................................................................................................................................................................... 56 3.5. Performance optimization and related issues in orchestrating simulations ............................................................................................................................57 4. Data interoperability ......................................................................................................................................................................................................................................... 57 4.1. Issues on data interoperability ...........................................................................................................................................................................................................57 4.2. Hard-coding for data interoperability .............................................................................................................................................................................................. 58 4.3. Framework specific annotations for data interoperability ........................................................................................................................................................... 58 4.4. Controlled vocabulary and ontology for data interoperability ................................................................................................................................................... 58 5. Testing integration ............................................................................................................................................................................................................................................ 59 6. Discovery, accessibility and ease of use of integrated systems ............................................................................................................................................................... 60 7. Discussion and conclusions ............................................................................................................................................................................................................................. 60 * Corresponding author. E-mail addresses: [email protected] (G.F. Belete), [email protected] (A. Voinov), [email protected] (G.F. Laniak). http://dx.doi.org/10.1016/j.envsoft.2016.10.013 1364-8152/© 2016 Elsevier Ltd. All rights reserved. 50 G.F. Belete et al. / Environmental Modelling & Software 87 (2017) 49e63 8. Recommendations ............................................................................................................................................................................................................................................. 61 8.1. User interface ........................................................................................................................................................................................................................................ 61 8.2. Model integration ................................................................................................................................................................................................................................. 62 8.3. Science components ............................................................................................................................................................................................................................ 62 Disclaimer .......................................................................................................................................................................................................................................................... 62 Acknowledgment .............................................................................................................................................................................................................................................. 62 References .......................................................................................................................................................................................................................................................... 62 1. Introduction better strategies for building integrated modeling systems. At first, our review was limited to integrated climate change mitigation A model is a simplified abstraction of reality (Schmolke et al., analysis systems. Due to the commonality of integration techniques 2010; Voinov, 2008). To answer questions related to environ- with other environmental domains, however, we broadened the mental problems, scientists and policy-makers, may need to scope to include integration of models in general. Our search used address complex issues at regional, continental, and even global key phrases of ‘integration of models’, ‘integrated assessment scales (Harris, 2002; Verburg et al., 2008). Developing all-inclusive study’ and ‘integrated modeling frameworks,’ and we considered models is difficult, however, and we must integrate individual 38 articles (see Table 1), of which 18 focused on specific integration models that represent specific domains (Gregersen et al., 2007). modeling systems (aka frameworks). Integration of models is becoming more important due to an To provide structure and context for