DESCRIPCIÓN Y HÁBITAT:

Chapter 2 discussed various methods for uncertainty management, including UA to quantify the overall output uncertainty as a result of all input uncertainty, and SA study how different sources of input uncertainty contribute to output uncertainty. The application of these methods was found to be limited by the use of multiple model evaluations, which can mean perform a single UA or SA could take several days to complete. This limitation can be removed by the use of emulators, statistical approximations of model simulators which are typically significantly faster to evaluate than a traditional model. However, accessibility of emulator methods is currently poor, requiring the user to undertake several data translation and model evaluation steps manually.

A tool for building emulators, consisting of a backend API and Web frontend, was designed and developed in Chapter 4, solving the problem of accessibility to emulator methods. The back- end API enables emulator methods to be integrated with existing software, whilst the frontend supports the entire emulation lifecycle in a user-friendly manner, providing interactive visualisa-

tions and parameter adjustment through forms. Further extensions were made to the tool to provide access to SA and probabilistic validation techniques.

The tool demonstrates the advantages of standard service interfaces and data formats in the Model Web, and may serve to encourage more models to be deployed on the Web. Once a model is exposed on the Web using either the processing service framework or WPS, given the inputs and outputs have data types suitable for emulation, the model will be immediately compatible with the tools. Integration between existing Model Web components and emulators was supported with the development of an extension to the processing service framework, allowing emulators to be uploaded, after which they are available in the same manner as any other model exposed using the framework.

Chapter 5 tested the applicability of the tools in the wheat yield case study, with a specific focus on emulating an existing third-party model for calculating crop yields, AquaCrop. The discovery of input constraints in the AquaCrop model resulted in a design upload extension to the emulation tools, further extending the applicability of the tools to models where range-based sampling may generate invalid input points. An AquaCrop emulator was trained, validated and deployed using the emulator upload service, allowing the simulator in the existing case study workflow to be replaced by the emulator with only a small number of changes. This case study demonstrated the benefits of emulator methods when performing UA, with the emulator evaluating 1000 points in under 5 seconds, compared to over 2500 seconds for multiple simulator evaluations.

While the tools were suitable for building and exposing an emulator for AquaCrop, the com- plexity of emulator methods, challenges with various Web service data formats and limited de- velopment time may restrict usage of the tools to a small number of models. Although emulation may not be applicable in all cases, the work can be considered to be a significant contribution to the Model Web tool set, providing a base for further generic tool developments and encouraging model owners and users to deploy their models on the Web.

6.1.3 Thesis aims and objectives

The conclusions of this thesis are given below, specifically relating the work in each to the objec- tives defined in Section 1.3.1:

• The emulation backend API and frontend support the construction of emulators, answering the first part of objective 1 outlined in Section 1.3.1, while additionally providing accessibil- ity to SA and probabilistic validation methods. Each step of the emulator building process

is supported by the tool, and the frontend provides a series of parameter adjustment forms and visualisations to help users train and validate an emulator surrogate for a Web-enabled model. The functionality provided by the tool represent a significant contribution to the tool set of the Model Web.

• The processing service framework adopts widely used technologies to expose processes and models on the Web. The framework allows processes to be exposed and consumed using standard interfaces and data encoding formats, without requiring the developer or consumer to have extensive knowledge of these standards. The adoption of the framework in Chapters 3 and 5 concluded that the framework can enhance the interoperability and usability of Web- based models, thus answering objective 2. However, the degree to which this objective has been met cannot be accurately quantified until the framework has been tested for a diverse range of models and use cases.

• A substantial amount of effort is required to deploy existing models on the Web. As the framework simplifies process development, the majority of this effort is in developing mech- anisms to communicate with models. To ease this burden in certain cases, a generic con- nector for MATLAB, and two libraries for third-party models were created, allowing these models, and those written in MATLAB, to be evaluated programmatically from the Web service interface (objective 3).

• An extension to the processing service framework was developed to allow emulators to be uploaded. Once uploaded, an emulator is available through the standard SOAP and JSON interfaces provided by the framework, and can therefore be used with code generation tools, existing clients, and included in a workflow as with any other model, in answer to the second part of objective 1.

• The FERA case study demonstrated that the processing service framework provides a suit- able platform for exposing models on the Web, through the exposure of three models to fa- cilitate a wheat yield change prediction workflow. Using the JSON interface, the workflow could be orchestrated in a JavaScript-based Web client, without a need for format-specific XML parsers. The construction and deployment of an emulator for the AquaCrop model is proof that the tools enhance access to emulator methods, and allowed the emulator to be integrated in the existing case study workflow, thus answering both parts of objective 1.