电子商务系统间建筑材料信息的交流平台--外文文献翻译.doc

外文资料翻译
英文原文
A platform for communicating construction material information between e-commerce systems[16]
E-commerce systems are becoming increasingly important in the Hong Kong construction material procurement market. Currently，however, many e-trading marketplaces have been developed, owned and/or hosted by different companies. Each of the e-trading marketplaces forms a closed system with their unique customers and clients. The totality of these e-trading marketplaces appears to be islands in the sea, as they are isolated with no interoperation between them. Since material information in each e-trading marketplace is limited，buyers usually cannot find all the required materials from one marketplace. This paper introduces a platform ，named ‘E-Union’, that enables interoperation between e-trading marketplaces. The ability of marketplaces to interoperate extends the idea of liquidity and network effect by joining more buyers with more suppliers，without sacrificing the ability of each marketplace to be highly specific to the supply-chain node or target buyer group it serves． This paper first discusses problems in a non-interoperable E-commerce marketplace environment. Then two approaches for enabling interoperation between marketplaces，the mobile agent approach and the Web services approach， are introduced．The third part presents the concept, system architecture and functions of the E-Union platform．
1 Problems in Non-Interoperable E-Trading Marketplace Environment
The Web-based e-trading marketplace contains two major functions：providing trading information and facilitating trading transactions. Users may log into the system as either buyers or sellers of construction materials. Sellers can upload their product information and find out summary information about their customers and their transactions. Buyers can search certain types of products，providing requirements such as brand，model, quality, price，etc.，or they can browse the products on display. When the products requested by a buyer are found，the information will be displayed to the buyer and the contact information of an agent closest to the buyer’s location will also be sent to the buyer. The buyer can negotiate with the agent about the price，or send an order to the agent by completing some forms online. If the user could not find the desired products，the system will keep the inquiry in storage for access by the sellers.
In recent years，several other construction e-trading sites have appeared on the Web. They are operated by different organizations and attract different client groups．They specialize in trading materials from suppliers in different regions. From time to time, however，clients of one e-trading system would like to buy materials that are not available in that system but are offered on other sites. One way to solve this problem is to let the client register with several e-trading marketplaces and search these sites one by one.
The variety and heterogeneity of different e-trading sites create problems for material purchasers. Finding materials in these sites requires material purchasers to acquire and maintain a list of web addresses, to interpret and understand the semantics and navigation methods in different sites，and to integrate product information in these sites for evaluation manually. These kinds of material finding jobs can be time consuming and the material purchaser is required to keep abreast of new e-trading sites as they come online．
To provide better value-added services to the clients，the concept of E-Union is presented by linking together relevant e-trading marketplaces so that cooperation between the e-trading marketplaces can be facilitated. In the e-trading union, when an e-trading site does not have the material requested by one of its registered clients，the site will send a request to other e-trading sites in the union. The remote e-trading site will treat the request as one from an associated client. An associated client cannot directly make use of the service of the e-trading marketplace as its registered client. When the material requested is found, the remote site will inform the requesting e-trading site, which will decide whether to submit an order on behalf of its client. Once a deal is made between the two e-trading sites，the requesting site will inform the remote site of the contact information of an agent to whom the material should be delivered. It will also display the material information to the buyer along with the contact information of the agent closest to the buyer’s location. The remote e-trading site will charge some extra amount of money，usually a certain percentage of the normal price, for providing the service．
2 Approaches for Enabling Interoperation between E-Trading Marketplaces
Since individual e-trading systems are developed based on different computational architectures，platforms and software, it is not a trivial task to make them interoperable. Several issues need to be addressed in order to realize the e-Union concept. The first issue is how an individual e-trading system finds the service from other sites and communicates with each other. The second issue is how systems understand the various kinds of data from other systems，such as the query，order，and product information. Specifically，the data may be in different formats and databases for representation and storage. This section discusses two approaches for achieving interoperation between e-trading marketplaces，the mobile agent approach and the Web services approach．
2.1 The Mobile Agent Approach
A mobile agent is a computer program that can autonomously migrate between network sites，i.e.，it can execute at a host for a while，halt execution，dispatch itself (together with its data and execution state) to another host, and resume execution there-all under its own control. It has been found that mobile agent is especially suitable for structuring and coordinating distributed applications running in a wide-area environment like the Internet. Such an environment is characterized by a large number of heterogeneous nodes with dynamically changing services and resources，high variation of connectivity both in performance and reliability，high variation of workload and network traffic, mobility of hosts，etc. .Mobile agents can move through the network of sites to search for, filter and process information needed to accomplish their tasks． Sending mobile agents to the remote server results in a large performance improvement because they can reduce the number of times one site contacts another and they can filter out non-useful information thus reducing the consumption of communication bandwidth． Furthermore，mobile agents bring flexibility and scalability into distributed，dynamic systems due to its ability to encapsulate policies，convention and algorithms and its ability to be dynamically created and destroyed．
In a mobile agent based framework，an e-trading site joins the union by broadcasting its address and service interface to other members in the union. The membership information is kept at each e-trading site in a database. Mobile agents are dispatched to other member sites for querying and ordering construction materials that are not available at the local site．
2.2 The Web Services Approach
Web services are used to promote software reusability over distributed systems． Distributed-Systems technologies allow applications to execute across multiple computers on a network A developed the ASP.Net platform for deploying Web services. In ASP.NET，the method calls are implemented through the Simple Object Access Protocol(SOAP)．SOAP is a platform-in-dependent protocol that uses XML to make remote procedure calls over HTTP. Each call and response is packaged in a SOAP message——an XML message containing all the information necessary to process its contents. HTTP was chosen to transmit SOAP messages because HTTP is a standard protocol for sending information over the Internet. The use of XML and HTTP enables different operating systems to send and receive SOAP messages. Another benefit of HTTP is that it can be used with networks that contain firewalls，the security barriers that restrict communication among networks. In addition，Web services use SOAP because of its extensive set of supported data types and its ability to send and receive attachments. Attachments are the most efficient way to send data such as pictures, XML documents，CAD files，etc., and this SOAP capability is extremely important for interoperation between construction material e-trading sites since material information is often presented in picture and CAD file formats．
Web services is a class that enables distributed computing by allowing one machine to call methods on other machines via common data formats and protocols，such as Extensible Markup Language(XML)and Hypertext Transfer Protocol(HTTP)． Microsoft Web services have important implications for business-to-business (B2B) transactions. Now, businesses are able to conduct transactions via Web services, rather than via custom created applications. Because Web services and SOAP are platform independent，companies can collaborate and use each other’s Web services without worrying about the compatibility of technologies or programming languages. In this way，Web services are B2B inexpensive，readily available solution to facilitate B2B transactions． Construction material e-trading sites can easily achieve interoperation by building their own Web services for other sites to use. A simple example is building material Web services that allow approved partners to search and buy their materials. In this implementation，the E-Union server serves its members by providing the members’ Web services information and directs the call for Web services to the appropriate member sites. Member sites provide Web services for searching and buying materials in their own site and charge those members who use their services．
3 The Web Services-Based E-Union Platform
A prototype system of E-Union using the mobile agent approach has been reported in Ref. This paper presents the Web services approach to implement E-Union. The Web services approach is selected for the future implementation of E-Union because of its default XML-based nature and its ease of providing system security. The XML-based nature is very important for inter-communication of construction material information since the popular standardization in construction material information，like bcXML and aceXML，are based on XML. Also, security in information transmission, which is vital to any B2B transaction，can be easily achieved in the Web services approach by transmitting information in a Secure Socket Layer (SSL)session. The following sections present system architecture and functions of the Web services based E-Union prototype system.
3.1 System Architecture
The Web services based E-Union system on developed in the ASP.NET platform． Currently ASP．NET can be installed in Microsoft Windows systems only but it will be available in other operating systems in the near future. ASP．NET supports a variety of programming language such as Visual Basic，Java，C+ +and C#． Thus Web services written in different programming language can be incorporated． The prototype E-Union system contains three servers: a construction material e-trading server named COME a surplus material e-trading server，and the E-Union server. The URLs of these three servers are http://come.bre.Polyu.edu.hk，http://waste.bre.polyu.edu.hk and http://eunion.bre.polyu.edu.hk, respectively. All the servers run ASP.NET in Microsoft Windows 2000 Advanced Server and use Microsoft SQL Sever 2000 Standard Edition as a database engine，Microsoft SOAP 3．0 for SOAP services, and Microsoft XML 4.0 for XML services．
The client，which is an e-trading marketplace registered in E-Union, first sends an HTTP/HTML request to the E-Union server. The application server in the E-Union server interprets the HTTP/HTML request， which stores material searching criteria. An SQL request is sent by the application server to the SQL server to find E-Union members that have the specified type of material. The application server in E-Union then sends SOAP requests to the appropriate member sites. A member site that receives the SOAP request sends an SQLXML request from its application server to its database server. The application server receives the SQLXML response from the database server and then sends the response as a SOAP message to the application server of the E-Union. The E-Union application server upon receiving all the responses from its member sites will combine all the responses and then sends it back to the client in HTTP/HTML format.
3.2 The E-Union Functions
The E-Union prototype system has two basic functions：1)database mapping，and 2)material searching. Before an e-trading site can use the E-Union functions，it has to first be registered on the E-Union server. The COME and the surplus materials e-trading sites have already registered on the E-Union server．
Alter registration，members have to tell E-Union about the material information they have through data base mapping. The first material information is about the type of material. E-Union contains a construction material classification with around 1100 types of materials．The second material information is about the attributes of each type of materials including unit，width，height，depth，unit weight，material，unit price，currency, brand，standard，country of manufacture，image，drawing，and additional material description files. The last information is about the database structure for storing the above two types of information，i.e., the detailed information about which database，table and field to search for the material information. For security of the E-Union members, this information will not be disclosed to E-Union but will be stored in the members 'own server instead．
The second E-Union function is searching materials in its member’s site. An E-Union member can use this function to search material information in the e-trading sites of other members. The searching starts from entering search criteria，including material type and material attributes. Once the search criteria is submitted to the E-Union server，the E-Union server will check the available members and the members' material information to see if they have the type of material required. The E-Union server will send SOAP messages to the members’ servers with the required material. Searching will be performed by the Web services in the members’ servers and results will be sent back to the E-Union server for display to the required member.
4 Conclusion
The prototype system of Web servers-based E-Union has been implemented successfully. Electronic marketplace for construction material trading can now join the E-Union to provide cross-marketplace searching for construction material information to its clients. The next stage