# SINDVis: User-Centered Dynamic Interactive Visualization System for Space Information Networks
## 3 Theory and Methods
### SINDVis Description of Functions
#### 3.2.2 Descriptions of TopolView Functions  
GeoView is responsible for the visual presentation and analysis of the entity domain. However, the expansion of SIN, and the increase in functions require an analysis of its topology structure and topology evolution. Therefore, it is necessary to make use of the ideas of the complex network. The space entities of SIN were mapped into network nodes, and relations between entities were abstracted as network links to analyze the network performance of SIN. Based on this, we designed TopolView in the topology domain. The aim of building the TopolView is to determine the network performance and network characteristics of SIN based on visual means, such as the importance of nodes, the key links, and the dynamic topology evolution laws. Therefore, we think that the TopolView should have the following functions. * **Function 1**: TopolView should show the complete topology structure of the SIN and realize the network expansion display of the four-layer structure. It should show the tight coupling relationships within the layers and the loosely coupled connections between the layers. * **Function 2**: TopolView should show the network features, such as the key nodes and important links of SIN, on the same page. The key nodes and important links are the core of the whole network, and they are the cornerstone of normal operation of SIN. Therefore, it is important for all people involved in the construction, development, maintenance, and management of SIN to master this information. * **Function 3**: TopolView should show the dynamic evolution laws of SIN. Under the guidance of topology evolution rules, including node increment, node deletion, link increment, and link deletion, it is possible to display the vibrations and changes in the network topology. Which are caused by the changes in nodes and edges in SIN. Within a certain time by the sliding of the time slice, it will keep a new stable state. * **Function 4**: TopolView should assist in the optimization of SIN through the cleanup of network topology-independent nodes and unrelated links, including the deletion of unimportant nodes and unrelated links. It should also optimize the SIN structure scale and reduce duplication in construction. TopolView is the main research part of SINDVis. The simulation and display of the TopolView of SINDVis is an effective method and means to construct and manage the SIN for USE-2 and USE-3. Therefore, the dependency on TopolView is also strong. This section describes the four functions above in relation to the different requirements. Similar to the GeoView, the topology domain view has many more functions than those described above, and they can be developed and expanded according to the needs of users. As discussed in the introduction, with the construction and development of SIN, its scale will increase continuously, and its structure will become more and more complex. Meanwhile, real-time changes in SIN topology will bring more uncertainties. All of them bring many challenges to the maintenance and management of SIN. In previous work, we established a weighted, dynamic evolution model based on local-world SIN [16]. The model combines the local-world phenomenon and edge-right features of SIN. However, the model only validates some characteristics of SIN from the network theory perspective. As we know, 70% of information acquired by people is done with the eyes. Meanwhile, visualization technologies not only formalize display views, but also can excavate hidden information behind views. Therefore, we think that we can also explore the dynamic evolution laws of SIN based on the dynamic visual view. Therefore, we initiated the idea of designing TopolView in the topology domain. On the one hand, TopolView can display the dynamic evolution processing of SIN. On the other hand, it can be used to analyze the changing relationships between the key nodes and core links of SIN.