# Data Access Based on a Guide Map of the Underwater Wireless Sensor Network
There is the problem of energy consumption in the process of data storage and query. Energy consumption is huge due to the long distances and long underwater data transmission times, and this will shorten the network service life while increasing background noise in UWSN. Hence, in the processing of data storage and query, energy consumption of data transmission needs to be reduced and balanced as much as possible for the purpose of prolonging the network lifetime. To address the challenges mentioned above, the goal of our work is to provide data access mechanism for storage and query real time data with less query time and energy consumption as possible. At the same time, this mechanism can support data discovery and large volume data aggregation for UWSNs. For this aim, a data access based on a guide map (DAGM) for the underwater wireless sensor networks was proposed in this paper, which is based on the metadata [7] and ring structure [8]. In DAGM, according to the shortest average user data query path of the network, a center ring structure composed of nodes was established for storing the metadata, which describes the abstracts of data content and storage location. For prolonging the network lifetime, the scope of network is divided into different areas. The sensor nodes in an area are formed into a cluster. When data is generated in the sensor node, the storage node is determined by the geographic harsh table (GHT) [9; 10]. The data is transmitted from the sensor node (data generation source) to the storage node being stored and the metadata generated for it, and metadata is sent to the center ring node that is the nearest to the storage node. After that, metadata is diffused and synchronized at the other nodes within the center ring, so every center ring node can store all metadata in a set for the network, and the data map can be formed. In the process of data query, when there are query data in any node (observation nodes, also called sink nodes are query users generally), the center ring node that is the nearest to it should be selected to deal with the query sentence. If there is no data meeting the user requirements in the map data, the query result \"_query failed_\" is given to the user; if there is existing data that the user requires, data transmission routing will be generated according to the storage location abstract described by the metadata, and the routing and specific data requests will be sent to the storage node. At the same time, the query result \"_ready to receive data_\" and data transmission routing will be returned to the query user. Lastly, specific application data transmission could be completed by the user and the storage node according to data transmission routing. In our study the main contributions are as follows:  
1. The DAGM system model is proposed so that the user (observation node) in an UWSN can access the specific application data and events it is concerned with as much as possible. The most challenging and difficult problems of DAGM have been analyzed;
2. The framework of DAGM is established. According to the shortest average query path of the network, the center ring structure composed of nodes is established for storing the metadata, and then the data map of the network is formed. In the meantime, data storage and query mechanisms are established to aid user access-specific application data and events quickly;
3. Data storage delay, data query delay, and a network energy consumption calculation model of DAGM are established, providing a method for the analysis of DAGM performance. The second section gives the system model and problem description of the work in this paper. The construction of data storage and query, architecture of the data map, and the mode of data storage and query will be discussed in Section 3. In Section 4, the performance of DAGM with respect to data access and energy consumption is discussed in detail. Simulation experiments and their results are given in Section 5.