Towards Spatial Information Services in LBS: A GML-based Approach

Fubao Zhu, Baohua Jin School of Computer and Communication Zhengzhou University of Light Industry

Zhengzhou,China fbzhu@zzuli.edu.cn

Jun Zhang No. 36 Institute

China Electronic Technology Company Jiaxing, China

beyond_zhang@126.com

Abstract—Location based service (LBS) is becoming one of the most promising application with the rapid development of wireless communication, mobile computing, and location positioning technologies. Now Geography Markup Language (GML) is emerging as the de facto standard in representing and exchanging geographic information that includes both the spatial and non-spatial properties of geographic features over the Internet. GML provides an open, vendor-neutral framework for the definition of geospatial objects, which makes it much more interoperable to use GML to integrate various sources of spatial data in LBS. This paper discusses the service discovery and spatial operation issues when using GML to enhance the performance of LBS based on web service. The architecture includes back-end database server, local spatial information server, global spatial information server, and J2ME client; the server adopts two-tie architecture, which includes global spatial information service and local spatial information service; the client is to access the remote spatial information service in all kinds of mobile terminals, and displays the contents of LBS services information. The prototype shows that this approach is feasible and efficient.

Keywords-LBS; GML; service discovery; spatial operation; web service

I. INTRODUCTION With the rapid development of wireless technology and

the availability of the variety of spatial data, as well as human’s nomadic instinct, they have not been merely satisfied by such simple services as receiving email, checking weather information using mobile device or obtaining information from desktops [1], but need more and more personalized and location-aware services, such as the traffic circumstance ahead, where they are, how can they find the nearest hotel, etc. Thus the location based service emerges as the times require with support by the mature technologies such as geographical information systems, global positioning systems, radio frequency identification, and other various location sensing technologies, especially the rapid growth of cell phone industry from the simple talk services to multiple functions of multimedia messaging and voice services [2].

LBS initially focused on consumers’ requirements and adopt the knowledge of a mobile device’s location to provide services to end user, e.g. tourism guidance, roadside assistance and entertainment facilities [3]. However, as the technology is maturing and pervasive, more and more services are used or will be used in business, government and industry, e.g. mobile office, emergency response, fleet and courier tracking, vehicle navigating, traffic monitoring, weather alerting, mobile

yellow page looking up, and location sensitive advertising, etc [4]. Much work has been done on location-related technologies and applications [5-7], and how to express location information to provide services for users in recent years [8-11]. Location based service discovery technology has been discussed in [12-14] and GML was used to facilitate the interoperability [15-18]. However, there are still many open issues, such as the heterogeneity, service discovery and spatial operations.

In this paper, we discuss the technical issues of service discovery and spatial operation. The GML is used to integrate the various sources of heterogeneous data, and web service technology and service-oriented architecture (SOA) is adopted to provide service for desktop users and mobile users. The server adopts two-tie architecture, which includes global spatial information service and local spatial information service. The client accesses the remote spatial information service in all kinds of mobile terminals, and displays the LBS services information with SVG.

The rest of the paper is organized as follows. In section 2, we describe the architecture of GML-based LBS running on web service and the interaction between clients and server. In section 3, the service discovery mechanism and the GML-based spatial operation are discussed. After this, a case study is discussed in section 4. Finally, the conclusions are given in section 5.

II. GML-BASED LBS IN WEB SERVICE

A. System Architecture The proposed system architecture use web service

technology, and adopts the Service oriented architecture, GML is used to wrap the various sources of geographic data, as shown in Figure 1.

Figure 1. Framework of GML-based LBS on web service

The server adopts the three-layer architecture, e.g., global spatial information server, local spatial information server, and database server. We use UDDI to publish global spatial service for its stable interface, thus it not

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DOI 10.1109/MVHI.2010.23

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only facilitates user access, but also provide standard interface for management and retrieval. While the local spatial information services are published by URL for the interfaces of these services are usually in change. The Clients may be fixed devices (e.g., desktop PC), or be mobile devices (e.g., cell phone, PDA, pocket PC).

In this architecture, SOAP protocol is used to finish gaining the spatial information service, WDSL is used to describe the interface for spatial information service, and UDDI and URL are combined to realize the distribution of spatial information. The system supports the transparent access, information sharing, and interoperation of multi-autonomous and heterogeneous spatial information service. The system consists of client, web server, database server, SOAP message, and other connecting facilities.

B. Interaction between Clients and Server Clients act as the interface between users and system,

to submit the user query and return the corresponding results, as shown in Figure 2.

Figure 2. Process of client accessing the remote services

The entire process goes as follows: • User logins at a client, and connects to spatial

information server. • Server checks the validation of the user identity,

and returns the result. • Client sends the query request submitted by user to

spatial information server. • Global spatial information server receives the

query request, and decomposes the query into sub-queries using its query decomposing and collaborating module.

• Global information server sends the sub-queries to local spatial information servers using interface proxy module according the data distribution.

• Local information server receives the sub-query, and data process engine finishes query operation and wraps the results into GML format.

• Global information server receives and integrates the results of each sub-query.

• Global information server sends the integrated query result to user.

III. SPATIAL INFORMATION SERVICE DISCOVERY AND SPATIAL OPERATION

A. Service Description and Publishing In order to provide much more spatial information

services for various end users, web services technology is adopted to describe and publish spatial information services.

Service description can be generated manually or created by the existing service interface definition. Developer can code all parts of the service description, including UDDI items. Some tools can generate WSDL from programming model and executable deployment of web service, and part UDDI items may be generated from metadata. Service description can be published by different publishing manners to service registry center.

The simplest publishing method is that service provider sends the service information directly to service consumer by email, ftp site, etc. A much more dynamic publishing method is to use DISCO (Discovery of Web Services) or ADS (Advertisement and Discovery of Services), which define a simple HTTP GET method from a given URL. Service provider will register on a spatial UDDI node for inter-host service description of enterprise. UDDI and URL are used to publish spatial information service in this study for different type of services. For global spatial information services, we use UDDI method, while for local spatial information services, URL method is employed, as depicts in Figure 3.

……

Figure 3. Framework for publishing spatial information services

Here, local spatial information services act as two roles: (1) to get the data needed for spatial information

service by accessing to data interface. The non-spatial information comes from database, while the spatial information is derived from the map application server.

(2) to publish its local services for global information server by registering on the spatial information service management center.

Global spatial information services act as three roles: (1) to manage the local spatial information services,

including the services registering, deleting, updating. It also can suspend, activate or trace a service.

(2) to publish its services on UDDI registry information center so that clients can access them.

(3) to provide spatial information services to the various service users or consumers.

B. Service Discovery After the spatial information services are created and

published in web services registries such as UDDI or WSIL documents, the users can search these services manually or automatically. The service discovery mechanism in this study adopts the basic methodology of service oriented architecture (SOA), as shown in Figure 4. Three different kinds of actors are involved in SOA: service providers, service requesters and discovery agencies. When a query request is submitted to an

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information broker, the broker will decide which of the registered sources should be used to answer the user request.

Figure 4. The basic service oriented architecture

Service Providers are the actual data providers wrapped up in a WFS/WMS interface. These interfaces accept request form the query processor and perform the various operations on the proprietary repositories. The retrieved data are described in GML format, and displayed as SVG graph. Service Requesters are users who can discover a service through WFS GetCapabilities request. This operation provides a description of the service, and the corresponding operations, parameters and data types. Service consumers can use this information to identify if a service provides the needed functionality and how to access it. Discovery Agency plays the role of service broker. It holds the global description for all the services and provides a standard interface for the service requesters.

C. GML-based Spatial Operation The data sources of LBS are usually come from

various repositories, and often are accompanied with different formats and the corresponding query language. GML provides an extendable and standard encoding mode of geographic information, which makes it easier for sharing, storage, and transport of these various sources of spatial data. The user’s query requests submitted to system will be transformed to various spatial operations, the result is returned as SVG to user, as shown in Figure 5.

Figure 5. GML-based spatial query model

Query of spatial information is classified as simple query and the spatial relation oriented query. For a simple query, local GML file cache is used to reduce the quantity of transmission in the network during the query processing, and to shorten the response time of the query. For a spatial relation oriented query, local spatial database cache is used to implement the query for data sources in file format. The query mechanism is implemented as follows:

For a simple query, Query Engine parses user’s query and extracts the part of simple query, then look up in the

local GML file cache according to the query condition. If hit, then return the resulting GML document to user, else Query Engine will find the corresponding data server and send the query request to the server. GML Wrapper transforms the spatial data into GML documents according to the query condition and returns them to Query Engine. Finally, Query Engine returns the GML documents to user and stores them in the local GML file cache.

For a spatial relation oriented query, different processing methods are employed for different data sources. If the spatial data are stored in spatial database, we need only to call them and transform the result into GML document, for the spatial database has already provided the functions to implement the spatial relation oriented query. While for the spatial data in file format, we need to import the files into the local spatial database cache, and then call the functions of spatial analysis to implement the spatial relation oriented query.

IV. IMPLEMENTATIONS AND EXPERIMENTS

A. Implementing LBS on J2ME J2ME (Java 2 Micro Edition) is a special edition of

Java introduced by Sun Microsystems, Inc. to meet the demand of information appliances which has limited system resource and network connection. It provides a robust, flexible environment for applications running on mobile and other embedded devices, i.e., mobile phones, personal digital assistants (PDAs), TV set-top boxes, and printers. The J2ME technology is based on three elements: a configuration provides the most basic set of libraries and virtual machine capabilities for a broad range of devices, a profile is a set of APIs that support a narrower range of devices, and an optional package is a set of technology-specific APIs. J2ME establishes a development and deployment environment for wireless clients and server.

WSA (J2ME web services APIs) extend the web services platform to include J2ME, and it enables J2ME devices to be web services clients, providing a programming model that is consistent with the standard web services platform. Figure 6 shows the framework of J2ME web services. In order to get the remote services on J2ME, five steps need to be performed: Get the WDSL document of the requested web service; create a JAX-RPC Stub class from the WDSL document; create an instance of the Stub class; call the methods of the Stub instance; and lastly, destroy the instance of the Stub. In these five steps, the most important one is how to access the remote web service by the Stub class.

Figure 6. Framework of J2ME web services

B. A Case Study A prototype of the proposed GML-based LBS service

discovery and spatial operation system is implemented in

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Java. The development software includes the JDK1.5, Weblogic Platform, DOM4J, Geotools, SQL Server, JBuilder, J2ME Wireless Toolkit, Oracle9i and Oracle9i Spatial. The geographic data in the system mainly are derived from the instances in ArcView GIS 3.2 and MapInfo 6.0. These data are stored in Oracle Spatial and file system. In this study, we use SOAP to get web services, and use WSDL to describe spatial information services. UDDI and URL are united together to distribute the spatial information services.

The spatial data in this study covers the cities, roads and provinces/states of Canada, USA, and Mexico. When enters the J2ME client interface, user can submit query request. User can select a map layer, e.g., the city, road, or province of Canada, and then submits the query request to system. The results are sent back to user, and displays on the mobile terminal devices, as shown in Figure 7, and Figure 8 shows the attribute information query.

Figure 7. Query interface of J2ME client

Figure 8. Map layer attribute query interface of J2ME client

V. CONCLUSIONS LBS is integrated application of spatial information and

mobile communication, combining the advantages of the spatial information technology (such as GIS, GPS, RS, VR and computer graphics) and the mobile communication technology (such as mobile locating, mobile inter-connecting and mobile terminal). In this paper, we discuss the issues and challenge in LBS, especially the data heterogeneity and interoperation. A framework of GML-based LBS on web service is described, where GML is used to wrap the various spatial data to form a universal operating interface, and the service discovery and spatial operation issues are discussed based on web service. Experiments show that the proposed method goes well when finding the location based services.

ACKNOWLEDGMENT This research was supported by Doctoral Research

Fund of Zhengzhou University of Light Industry (No. 2008BSJJ012); Open Research Program of Key Lab of Earth Exploration & Information Techniques of Ministry of China (No. 2008DTKF008).

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