672 ITU‐T's Technical Reports and Specifications 3.4.1.2 Scope Through the model service interface, model providers can perform the registration, insertion and publishing of the model metadata; model consumers are able to query model metadata information, find the model in need and finally discover, access and invoke the model according to the model ID returned. The model service interface specification can be exploited for the publishing, sharing and reuse of the models. The concrete application scope of the model service interface specification is depicted in Figure 17. Figure 17 – Application scope of the model service interface specification under the environment of the integrated management for smart sustainable cities 3.4.1.3 Content The model service under the smart city environment is an open interface, and it acts as an intermediate agent between the user and the model storage warehouse. A web service interface is defined in the service interface specification, in which queries about the model metadata, input and output, as well as representation for models are allowed. Moreover, the methods of registering new models, deleting existing models, as well as inquiring about new models are all defined in the model service interface specification [b‐de Castro]. There are three kinds of operations in the interface specification, namely core, transactional, and enhanced operation. Core operations include the GetCapabilities, DescribeModel, and ExecuteModel operation. Transactional operations consist of the InsertModel, DeleteModel, and UpdateModel operation. Enhanced operations are composed of the GetFieldOfInterest and GetModelByFunction operation. Among all these operations, only the three core operations are mandatory, while the others are optional. The element structure for the model service interface specification is as explained in Table 1. Online sharing for models Unified management for models Combinations for models Efficient discovery of models Quick access to models Reuse for models Model Service Interface Specification for Integrated Smart City Management Terrain model Prediction model Evaluation model Diffusion model Atmospheric model Hydrologica l model Transportation model