Design and Implementation of Heterogeneous Sensor Registry ...

Design and Implementation of Heterogeneous Sensor Registry Category Service XunLiang Yang, Nengcheng Chen, XiaoLei Wang State Key Laboratory for Information Engineering in Surveying, Mapping and Remote Sensing Wuhan University Wuhan, China [email protected] , [email protected], [email protected] Abstract—with geographic information resources continuous expansion and the rapid development of the web technology, the demand of integration geographic information resources become increasingly strong. Category Service for the Web (CSW) is the fundamental Service for registering and querying sensor information in the Internet. This paper is dedicated to design and develop a heterogeneous sensor registry category service system GEOSENSOR-CSW. In order to improve the completeness of the sensor information stored in this system, this paper adds new elements of ebXML Registry Information Model (ebRIM) and add new mapping relationships of Sensor Model Language (SensorML) element and ebRIM element. This paper registers some hydrological sensors which are used to monitor flood into GEOSENSOR-CSW successfully and analyses those mapping relationships of some hydrological sensor information elements between SensorML document and corresponding ebRIM document mainly. The experiment result shows that GENOSENSOR-CSW can improve the completeness of the sensor information stored in this system effectively. Keywords—Sensor; Category Service for the Web; Sensor Model Language; ebXML Registry Information Model; mapping relationship

INTRODUCTION In flood monitoring, hydrological sensor plays an important role. For example, hydrological sensor can be used to monitor area of flood region, flood level and so on. Hydrological sensor is various and amount of hydrological sensor is large. For example, according to work mechanism of sensor, sensor can be divided into radar sensor, photography sensor, scanning sensor and others. With the development of sensor technology, more and more sensors can be used to monitor flood. So, the registry and management of hydrological sensor is very important for sharing hydrological sensor resources and improving interoperability of hydrological sensor. Effectively registry and management of hydrological sensor can contribute to real-time discovering, simply publishing and management of hydrological sensor effectively [1] [2]. 52N-SIR (Sensor Instance Registry) has implemented the registry and searching functions for sensor information in the system [3]. But the description information of sensor is too less to meet the actual demand. This system needs to connect the Category Service for the Web (CSW) and the system’s service is not a direct sensor registry service. Deegree has implemented the category service of metadata for geographic information,

but it not contains function models of directly accessing data. GeoNetwork has implemented the category service which supports the accessing, inserting and updating metadata of geographic information. But the description of spatial relationships is not complete. George Mason University (GMU) has its own CSW which has implemented basic functions for registry and discovery of metadata of geographic information or service. CSW system plays an important role in registry and management of sensor information. However, those following problems need to be solved. • The indirectly registry of sensor information. Some existing sensor registry services need to connect the general CSW. When inserting sensor information into System, Sensor information will be successfully inserted only after the connection between System and CSW building successfully. This method of sensor registry service would make information loss and increase system run-time for sensor inserting, querying and other operations greatly. • The information for sensor registry is not complete. Existing sensor registry service systems cannot preserve all useful sensor information. For example, 52N-SIR only can register system and component, not including the nonphysical process, and the mapping relationship between Sensor Model Language（SensorML）and ebXML Registry Information Model (ebRIM) is incomplete. The mapping relationship of 52N-SIR only includes observedBBox, ID, longName, shortName, description, input, output, location and validtime. The preserved Information in 52N-SIR cannot meet the acquirement of discovering sensor information for no description information about connection and parameters effectively. CSW which bases on ebRIM can effectively manage metadata of geographic information, such as retrieval and management of metadata of sensor, binding with specific application and metadata information model, building content information and functions to meet itself requirement, providing query functions for clients[4][5]. SensorML provides a framework to describe heterogeneous sensor information [6]. Heterogeneous sensor information is mainly described by sensorML, including hydrological sensor, for example ground monitoring site and satellite platform [7]. So GEOSENSOR-CSW should implement the function of registry

of sensor which is described by sensorML. EbRIM defines a mechanism to establish the relationship between different metadata as well as a comprehensive classification mechanism [7]. EbRIM model defines a variety of metadata types, these metadata types would be divided into six categories, namely core information model, association information model, classification information model, provenance information model, service information model, event information model and cooperating registries information model [8]. Because of those six categories, if sensor information can be extracted from sensorML document and be preserved as ebRIM format, sensor information can be queried and managed much simpler. According to the discussion and analysis as described above and demand of the effective management of heterogeneous sensors, this paper implements sensor registry service system GEOSENSOR-CSW and perfects sensor registration information mapping relationship of SensorML to ebRIM, designs and implements registration of multiple types of sensors. The organization of this paper is as follows. Section II presents the architecture and technologies of registry category service system GEOSENSOR-CSW. Section IV outlines the key method and technologies, including mapping relationships of SensorML and ebRIM. Section V shows the result of Registry Category Service experiment. Section VI discusses and summarizes advantage and future work. DESIGN Architecture and Technologies As shown in Fig. 1, GEOSENSOR-CSW bases on B/S architecture. This architecture is divided to three layers, namely presentation layer, business layer and persistence layer.

and invokes other components of this layer. Business layer can transport result to persistence layer or presentation layer. As show in future, this layer contains user login and management function model, getRecords function model, transaction function model, getRecordById function model, getCapabilities function model, batch operations function model, SensorML transaction function model and xml parse and produce function model. Presentence layer is used to preserve processing result of business layer in relational databases. In business layer, the most basic and important function model is xml parse and produce function model. Because other function models need this function model to parse xml document and extract content information of xml document or produce the xml document when need. For xml parse and produce function model, completeness of information of xml document is the critical factor. So when translating SensorML to ebRIM, this paper extends element types of ebRIM to translate more information of SensorML to ebRIM information through extending mapping relationships of SensorML to ebRIM. Extending elements and types of ebRIM As show in Fig. 2, the core element of ebRIM is RegistryObject element. Other elements of ebRIM all implement it. RegistryPackage element of ebRIM is an abstract class. It encloses sensor extensive elements, includes sensor type and intended application. Process_Category (instance of RegistryPackage) can be regard as Folder and instance of RegistryObject element can be regard as File. Registry of Sensor in deed is inserting instance of RegistryObject into system.

Fig. 1. The Architecture of GEOSENSOR-CSW

The presentation layer is mainly used to display the user interface, the result from business layer, gather and submit user input information to business layer models. Business layer processes input information which is from presentation layer

Fig. 2. Extending elements of ebRIM

• Extending types of ExtrinsicObject element. Sensor can be described by the System element and Component element.

If need to identify type of sensor, objectType attribute of ExtrinsicObject element can make effectively. • Extending types of Association element. Subclasses of Association include AccessibleThrough, ComposedOf, Contains, InputConnection and OutputConnection. Those types of Association would be declared and used in the structure of RegistryPackage. These five types of Association could be regard as value of classificationNode and added to the ClassificationScheme element of AssociationType. When need to identify AssociationType of sensor information, associationType attribute of Association can do work effectively. Extending type ComposedOf is used to describe the relationship of element ProcessChain and element System or Component. It can be used to build the relationship between sensor and platform. Those relationships can be built though input parameter which described by attribute InputConnection and output parameter which described by attribute OutputConnection. Extending type Contains is used to describe relationship between sensor and algorithm. The type AccessibleThrough is used to describe relationship between service and sensor. • Extending types of ClassificationScheme. According to different sensor types and intended applications, we extend types of ClassificationScheme, ClassificationNode and Classification. This paper builds two Classification frameworks for all processes. The first one is intended application which is used to describe the sensor application domain; the second one is service type, such as Sensor Observation Service (SOS), Sensor Planning Service (SPS). Also we build two classification frameworks for sensor. SensorType and OrbitType. SensorType is used to describe platform type, such as Satellite platform; OrbitType is used to describe orbit type of sensor, such as sun synchronous orbit, ground post. • Extending types of Slot. This Paper use Slot element to describe some sensor specific features. The extending types of Slot include keywords, position information, observed bound, validtime, input parameter, output parameter and others. Extending mapping relationships of SensorML to ebRIM As show in Fig. 3, the mapping relationship mainly contains mapping relationship of objectTypes, Associations and attributes. According to matching result of selected registry object type and ObjectType attribute of ExtrinsicObject element, the registry object type can be judged. For example, when judging attributes mapping relationship of System element, if a system has some components, ComposedOf relationship will be built between each component and this system. If a system has some services, AccessibleThrough relationship will be built between each service and the system. If a system has some connections attributes, OutputConnection and InputConnection will be built between each connection element and system.

Fig. 3. Extending mapping relationships of SensorML to ebRIM

Attribute mapping relationships of sensor include several sections as follows. • Mapping of basic information. For example, urn attribute of sensor (system or component) described by SensorML can be mapped to value of id attribute of ExtrinsicObject element of ebRIM. Name and description information extracted from SensorML document can be mapped to values of rim: Name and rim: Description element of ebRIM document. Attribute information of relevant organization and person extracted from SensorML document can be mapped to rim: Organization of ebRIM document. • Mapping of classification. When classifier element occurs in SensorML document, we could extract and insert attribute information of classifier into ClassificationNode according to architecture of ClassificationScheme. For example, if sensor type for registry is system, firstly, information of system would be stored to attributes and content ExtrinsicObject element; secondly, we can create PlatformType and SensorType classificationNodes and insert those elements into classification frameworks, then connect according objects with classificationNodes by creating classifications element. • Mapping of specific attribute. Some specific attributes can be mapped to slot types with different attribute values of ebRIM. IMPLEMENTATION Base on specification of CSW and ebRIM, we design and implement a Sensor Registry Category Service System by using Java program language and PostgreSQL Database. Its name is GEOSENSOR-CSW. The follow figure is homepage of GEOSENSOR-CSW. GEOSENSOR-CSW implements some basic and special functions compared with other similar System as follows.

monitoring adopts many types of hydrological sensor platforms and hydrological sensors, such as Landsat-7, SPOART, Ground monitoring site and others. Registry service system can register and manage a large number of heterogeneous hydrological sensors [9] [10]. Experiment Data The experiment data includes MODIS_AQUA sensor information which is described by SensorML document and the sensor can provides observation information for flood monitoring. Experiment Result The experiment is mainly used to validate new elements of ebRIM and new mapping relationships of SensorML to ebRIM can improve the completeness of sensor information stored in GEOSENSOR-CSW system. Fig. 4. Homepage of GEOSENSOR-CSW system

GetCapabilities operation The operation is used to describe service Capability of GEOSENSOR-CSW, which return information of this system function and parameters. GetRecordById and GetRecords operation The operation is used to discover and get sensor information which meets query conditions. Query condition contains sensor keyword, sensor name, observed bound validtime, sensor position and so on. If need to query the specific sensor information, client can use GetRecordById though providing the sensor id. If want to get some sensor by given some query parameter conditions, client can use GetRecords operation to do it. Transaction operation The operation contains three sub-operations: Insert operation, Delete operation and Update operation. Insert operation is used to register sensor information. Delete operation is used to delete sensor information from relational database. Update operation is used to update sensor information. GEOSENSOR-CSW also implements sensor batch insert, delete and update operation which are not implemented by other similar systems. Client can register sensor information through three methods: directly input some sensor key parameters, SensorML document of sensor information and normal Transaction-Insert document of sensor information. CASE STUDIES Flood is a serious horrific disaster of agriculture in China. So, flood monitoring is an important way to relieve extent of flood loss. Flood monitoring needs relevant information which can be obtained by hydrological sensor detecting. Flood

This paper will compare the MODIS_AQUA SensorML document and the corresponding MODIS_AQUA ebRIM document mainly. As shown in Fig. 5, the element “connections” of SensorML describes input parameters and output parameters of sensor information. Those parameters information is important for sensor collaborative observation. In GEOSENSOR-CSW, Those parameters information would be extracted and saved in the element Association of ebRIM. The element Association can use attributes and sub-elements to save information detail. For example, if the value of attribute associationType is “inputconnection” which not exist in original ebRIM, it shows that the element Association preserves the association type between sensor and input parameters; else if the value is “outputconnection” which not exist in original ebRIM, it shows that the element Association preserves the association Type between sensor and output parameters. Information of Sub-elements of element “connections” can be transmitted in ebRIM by using element Slot, value of sub-element “source” and “destination” can be saved as the value of sub-element “value” of element Slot. The element “interfaces” of SensorML defines information of sensor service type, service access address and service specific sensor id. When translating SensorML document to ebRIM document. The element content can be extracted and saved as the value of element Slot of ebRIM. The attribute “name” of element Slot has different value, correspondingly, ServiceURL, ServiceType and ServiceSpecificSensorID (those values all have the same prefix –“urn: ogc: def: interface: OGC: 1.0 :”). Those values are new values of element Slot. It should be pointed out that units would not be extracted from SensorML or transmitted to ebRIM, because those units are fixed. When querying specific sensor information, we can get information of sensor information unit through queried sensor attribute or field.

Fig. 5. some mapping relationships of MODIS-AQUA information SensorML document and ebRIM document

DISCUSSION Direct registry of sensor Compared with 52N-SIR system, sensor information can be registered and queried directly in GEOSENSOR-CSW. Loss of information can be avoided by directly registry method. The registry method provided by 52N-SIR is one-off and every time updated which affects sensor data timeliness. The registry method provided by GEOSESNOR-CSW realizes the data synchronous update and other operations which are convenient for discovering, preserving sensor data and reduce the system run-time. Improve the completeness of Information of sensor Compared with 52N-SIR, information of sensor which would be preserved not only includes description information of sensor, reference frame information, identification information and service reference information, but also includes intended application, sensor type and others. GEOSENSOR-CSW not only realizes the mapping relationship of SensorML to ebRIM, but also realizes the translation of parameters and connections attribute information and adds new association types and classification information. The design of

mapping relationship contains the mini set of conditions for sensor searching and assures the accuracy and completeness of stored sensor information. CONCLUSION This paper designs and implements GEOSENSOR-CSW registry category service system, which can be used to register multiple types of sensors, including hydrological sensor. New elements of ebRIM and new mapping relationships of SensorML and ebRIM improve the completeness of sensor information saved in GEOSENSOR-CSW. In the future, our work will occur on the improvement of interoperability of registry method [11] and the application of semantic technology in Category Registry Service System. ACKNOWLEDGMENT This work was supported by the National Basic Research Program of China (Grant No. 2011CB7071), The National High Technology Research and Development Program of China (Grant No. 2013AA01A608), the National Natural Science Foundation of China (NSFC) (Grant No. 41171315), and the Fundamental Research Funds for the Central Universities of China (Grant 2012619020203).

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