# A Survey on Data Storage and Information Discovery in the WSANs-Based Edge Computing Systems
## 3 Analysis of the Data-Storage and Information-Discovery Schemes Proposed for WSANs
### Comprehensive Comparison and Analysis  
From the description and the analysis presented above, we can see that the existing schemes based on the query-driven model mainly store the sensing data in a distributed way among the sensor nodes, and it can hardly achieve the real-time information discovery. As for the existing schemes based on the event-driven model, although sending the data directly to the actuators to get stored can shrink the delay of discovering the event information, the energy consumption on updating the latest locations of the actuators across the network should attract our attention if the actuators move frequently. Moreover, if the amount of the sensing data is large, sending them all to the mobile actuators, which may not be located at the optimal storage locations because of carrying out the tasks, will not be energy efficient. To illustrate the performances of the above-mentioned WSANs-based Edge computing systems on different metrics clearly, we make a tabular presentation in Table 1.  
Figure 6: The architecture of the REFER system [48] (source node 210 wants to send an event report to node 201, and it sends the report along the route 210\(\rightarrow\)102\(\rightarrow\)020\(\rightarrow\)201 where “\(\rightarrow\)” denotes an unidirectional link. In the case that node 020 is broken, node 102 can independently find out an alternative route, namely 102\(\rightarrow\)021\(\rightarrow\)212\(\rightarrow\)120\(\rightarrow\)201, to route the report to the destination without requiring the source node to retransmit the report). Possible Solutions to Achieve the Multi-Objectives on Data Storage and Information Discovery in the WSANs-Based Edge Computing Systems  
In this section, we discuss potential technologies to achieve multi-objectives, such as high energy efficiency, high load balance and perfect real-time performance for data storage and information discovery in the WSANs-based Edge computing systems. First of all, collaborative mechanisms for data storage and information discovery in WSANs should be researched and utilized. Both sensor nodes and actuators in WSANs should undertake part of the tasks of data storage and information discovery to improve the utilization ratio of the storage capacity of all types of nodes in WSANs and the load balance of WSANs. From the analysis presented in Section 3, we notice that the existing data storage schemes in WSANs either store all data on sensor nodes or store them all on actuators. It is hard for those schemes to achieve the above-mentioned multi-objectives in WSANs, the reasons of which are described as following: (1) consider the case that all data are stored on the actuators in WSANs. In this case, if sensor nodes send their sensing data directly as soon as the data are generated, each actuator must broadcast its latest location every time when it moves to a new place so that sensor nodes are able to know where to send their data. Moreover, because the events may occur at any time and any place in the network field and actuators must move to the places where the events happen to deal with them, it is impossible for the actuators to stay at the optimal storage locations all the time. Thus, it is hard to achieve high energy efficiency on data storage if all data are sent to the actuators and stored as soon as they are generated. It is straightforward to propose to let the actuators collect the data just like the data-collection schemes based on mobile elements in WSNs. Of course, this is energy-efficient, but its real-time performance would be compromised because it takes a lot of time for the actuators to move and collect the data of all the sensor nodes, especially when the network fields are large; (2) consider the case that all data are stored on sensor nodes in a distributed way. In this case, the actuators have to launch queries to search for the data that they are interested in. On one side, if the query frequencies of the actuators are low, it is impossible to achieve real-time information discovery.