Workflow-Oriented the Optimal Path Web Services in Multi-Level Road Network Yumin Chen School of Resource and Environment Science Wuhan University Wuhan, China
[email protected] Abstract—Usually, a typical city road network is very huge, including thousands upon thousands of nodes. If several cities are considered, even countrywide or larger area, the classical algorithm is very difficult to get a correct result. To solve this problem effectively, when a mass of data is given, distributed multi-level road network data is considered. It builds pyramidliked data model, calculates the optimal path analysis in multiple layers, and then conflates the final results by sub-result coming from multi-levels. With development of Web Service technology and Internet network, it provided necessary preparation for data sharing and interoperability of distributed information. So it provides technique support for a dynamical building of pyramidliked multi-level road network data model and an optimal path service. Workflow technology can effectively build all data sharing web services and functional web services into one executable service chain. Using self-developed workflow software will combine related web services into an abstract service chain. The abstract service chain is mapped into BPEL standards service chain. Finally, the Active BPEL workflow engine will be used to implement the service chain, and the results will be sent to the client. The service application proves that the optimal path service on multi-level road network is feasible and efficient to deal with large area optimal path analysis problem. Keywords-the optimal path web services; multi-level road network; workflow-oriented
I.
INTRODUCTION
With the increasing of data quantities of road network and dispersive management of data in different departments, the following problems are often encountered when optimal path computing is conducted in large region. 1) It is difficult to obtain needed large region scope and detailed data of road network, only from one map. Usually, more maps are used at the same time to acquire the needed large region data; 2) Because the storing and updating is performed in various departments, it has much more difficulties to acquire all needed data form one computer. To make thing easy, it is needed to use more computers distributed in different geographic space. 3) How can optimal path calculating work effectively in multiple computers and maps?
Jianya Gong, Haitao Cao, Zhipeng Gui State Key Laboratory of Information Engineering in Surveying, Mapping, and Remote Sensing Wuhan University Wuhan, China According to above questions, this paper puts forward the research method of optimal path services of multi-level road network, facing workflow. Using the workflow mode of service, and considering more map data of more severs, on the basis of data ranges and map scales and other related information of related maps, and according to unified rules, a pyramid-like data model of multi-level road network is built. II.
QUESTIONS
Following questions are needed to handle by the workfloworiented optimal path web services in multi-level road network: 1) How will the required road network data be obtained in distributed database servers? 2) How will the pyramid-like data model of the multi-level road network be constructed, using multiple road networks? 3) How does the optimal path analysis word in the data model of multi-level road network? 4) With workflow mode and using different web services, how is the service chain built, which is implemented by workflow engine according to the users’ requirement? For the first question, web services provided an effective technical supporting for the sharing and interoperability of distributed data. To satisfy the need of data sharing, the standard specification of web map service(WMS), web feature service(WFS) and web coverage service(WCS) clearly define a set of service interfaces. Currently, various large GIS software, such as ArcGIS, MapInfo, GeoStar and so on, supports the standard interfaces of WMS, WFS and WCS gradually. The data sharing services provided by different areas, different scales and different GIS platforms are used as multi-level road network data needed in the system. It well supports the dynamical building for pyramid-like data model of multi-level road network that related road network data are got through finding the needed services, which are registered in the registry centers, such as UUDI, EbRIM and so on. As the obtained data being used in the operation of path analysis, the service of sharing data, WFS, is selected, by which the road network data are acquired. And the road network data is saved as GML document as the unified criterion for transportation [3].
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For the second question, pyramid-like data structure of multi-level road network is built using multiple data which are acquired from the road network data of different scales and scopes in WFS service. Small scales data, such as the data of 1: 4 million, 1:1 million, are set at the bottom of multi-level road network; Large scales data, such as the data of 1:10 thousand, are set at the top of multi-level road network to build a pyramid-like structure which gives a coarse-to-fine description of the data information. In the case of complete attributes information and small data quantity, multi-level road network is built with the data which are acquired according to the road attribute information. Also, pyramid-like data structure that is form whole to part is built by putting main trunk in the bottom, and putting subsidiary trunk and detail information in the top. For the third question, classic Dijkstra is used as the optimal path algorithm. However, there is a problem that how to combine the Dijkstra algorithm with the data model of multilevel road network. Using Dijkstra algorithm step by step in the road network of every level, every optimal path is calculated, and then, all of the optimal paths which belong to every segment separately are combined to a whole optimal path, the detailed algorithm of which is showed in the literature [2]. Aim at the fourth question, it is the main work of this paper that using workflow mode to construct a whole service chain based on the different services.
processing for workflow. Acquirement for road network data means that finding needed data through available services registry center and according to different scales, building pyramid-like data model of multi-level road network using obtained road network data, based on which optimal path analysis is carried out. From data services, data model services of road network to analysis services of optimal path, processing mode for workflow is used to build a complete service chain. Treatment processes for workflow is that: building abstract service chain model firstly. Abstract service chain is a service chain accorded with logical relation which is built using related data services and function services and according to the sequence in which the services are executed and recorded using self-defined formats. Then, self-defined formats of service chain are converted into standard BEPL documents. Finally, the result is obtained by executing the documents using BEPL engine. The client terminal mainly provides browsing operation for road network data, inquiring for road network information, path analyzing through the starting point which is assigned by users and needed to be inquired and calling the services in the server terminal, visualizing the final analyzed result by execution of the workflow.
From the analysis for the first three questions, it is obviously that optimal path service is constructed with a serious of web services which contain acquiring the needed road network data in the distributed computer servers, constructing pyramid-like data model of multi-level road network based on all kinds of road network data, performing optimal path algorithm of every road network by using Dijkstra algorithm step by step, getting the complete result of optimal path by combining the optimal path in every level. With workflow technique and based on the services which are related with the construction of multi-level road network and the calculation of optimal path, an executable service chain can be built effectively. An abstract service chain accorded with logical relationship is built, using the selfdesigned workflow software and base on related services which contain sharing data services of road network of WMS/WFS, the construction services of multi-level road network, the optimal path services of Dijkstra, the allocation services for optimal path calculating in every level and related services obtained the finally whole path. An abstract service chain is mapped into a BEPL service chain accorded with common standard.
IV.
WORKFLOW TECHNOLOGY
Workflow-Oriented the optimal path web services system mainly contains server terminal and client terminal, whose overall framework is showed as Figure 1.
It is understood form the designing framework that the system deals with data services and processing services and so on. For example, data sharing services, construction services for multi-level road network model and optimal path calculation, etc. The needed research contents lie in how effectively to make each service performed automatically and in passing series to obtain the final result.
The server terminal mainly consists of acquirement for needed road network data, construction for multi-level road network model, calculation services for optimal path and
ISO19119 constructed the service framework of OGC, and proposed the concept of service chain. According to the roles users play in their establishing and controlling, service chains
III.
SYSTEM FRAMWORK
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are divided into three types: namely user defined (transparent) chains, workflow-managed (translucent) chains and aggregate service chains(opaque). And based on oriented graph, the thinking of visual representation of service chains is proposed [5]. However, for consisting of elements, combined mode and flow control, there barely is clear definition. At present, the research of service chains models of geographic information is mainly centralized in how to better use the available specification of IT fields, for example, WSBPEL、WSCDL、WSFL, to implement the construction for service chains. The environment network supported services of ESA directly uses business process execution language (WS-BPEL) for the construction of geographic information service chains to provide cooperation environment for service providers [6]. L. Di (2006) provided overall modeling scheme driven by identity (namely abstract flow modeling, instantiation, execution), in which service chains are described by OWL-S and implemented by being changed into WSBPEL [7]. For better intuition and simplicity of service chains model, self-defined model (namely Abstract Service Chain Model with Data-dependent based Directed graph and Block structure) is used [4]. Data nodes, service nodes, geographic information treatment process, constrained condition of service chain and meta data information involved in service chains are described in this model. The model totally defined four types of elements: (1) Data node, which is used to describe original data, middle data of final result data and all kinds of variable parameters in processing flow. (2) Service node, which is used to describe some processing operation in processing flow and divided into two types, namely atomic services and aggregation services. (3) Link object, which is used to describe link object and transformation mode between service and service, service and data. (4) Description for the attribute and constrained condition of service chains. Because it is a model of abstract service chains, this model can not be executed indirectly. After construction, syntactic and semantic validation, the model can be transformed into execution service chain accorded with WS-BEPL specification, which is implemented by the engine of WS-BEPL service chain. The optimal path service chain of multi-level road network is built using the above model of abstract service chains, whose process mainly contains following steps, and flow chart is showed as Fig2. (1) Building the abstract service chains of multi-level road network. The main flow of abstract service chain is obtaining the information data of different scales by data services of WFS, using acquired data to construct the model of multilevel road network by model construction services, executing the optimal path calculation by calling network analysis services and getting the result. (2) Instantiating abstract service chain: namely combining each practical operation with each wsdl document of relative practical service.
(4) Model transformation: mapping the abstract service chain model to standard BEPL model. (5) WS-BEPL flow editing: adding assignment operation and optimal model. (6) WS-BEPL flow publishing: deploying WS-BEPL flow into appointed engine in order to manage and calling execution.
V.
THE EXPERIMENT
Optimal path system of multi-level road network is implemented, using WFS road network data services provided by available GIS software, for example ArcIMS, MapInfo, as data source, and using WMS、WFS interfaces supported by GeoStar to provide road network data sharing services of system. Chinese road network data of 1 : 4 millions,1 : 1 million road network data of Hebei and Hubei province, and 1 : 10 thousand road network data of Beijing and Wuhan city are acquired from various data servers, which are as experimental data. The data model construction services and optimal path calculation services of multi-level road network are built in the platform of Microsoft Visual Studio.Net. Wuh
Third level
Beijing
an
(1: 10 thousands city data) Second level (1: 1 million province
Hubei province
data) First level (1: 4 millions country data)
Figure 3.
Model construction of multi-level road network
(3) Validating the service chain model: examining whether grammar or semantics problems exist in abstract service chain or not.
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Beijing
Coarse-to-fine pyramid-like data model of road network is used to build data model of multi-level road network. The data model of multi-level road network is constructed using 1 : 4 millions data as the first level of road network, 1 : 1 million data as the second and 1 : 10 thousand s as the third, which is showed as Figure 3. The abstract service chain of multi-level road network analyzing workflow is designed using GeoChaining which is a self-developed software of constructing service chains, which is showed as Fig 4. After the validation for service chain model, the abstract service chain is transformed into an executable service chain accorded with the standard of WSBEPL. Finally, WS-BEPL service chain is executed by Active BEPL workflow engine and the result is delivered to the client terminal as the form of pictures. The optimal path calculation between Peking University and Wuhan University is executed, and the red line in Figure 5 shows the calculation result. Figure 5. Optimal path calculation result of multi-level road net work
ACKNOWLEDGMENT This research is funded by National Nature Science Foundation of China (project NO. 40601082), 863 projects of China (project NO.2007AA120501) and 863 projects of China (project NO.2007AA12Z217). The authors would like to thank NSFC Project and 863 Project for these supports. REFERENCES [1]
[2]
Figure 4. Abstract service chain of optimal path for multi-level road network
[3]
[4]
VI.
CONCLUSIONS
Based on all kinds of relative data services and function services, a service chain is constructed using workflow technique in the service system of multi-level road network oriented workflow. When users need to call a service, it will be executed by workflow engine and the execution result will be returned. This method is workable from the experimental results of the system. The data services of road network, construction model of multi-level road network and the functional service of optimal path analyzing can be joined up by workflow construction tools, which can provide an analyzing method for users.
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