第7章 WebGIS的體系結(jié)構(gòu)

1、第第7章章 WebGIS的體系結(jié)構(gòu)的體系結(jié)構(gòu)Reference AA. Alesheikh, H. Helali, HA. Behroz, Web GIS: Technologies and Its Applications, 2002 OpenGIS相關(guān)文檔 唐大仕，博士論文，空間信息WebServices 若干關(guān)鍵技術(shù)研究，2003本章內(nèi)容本章內(nèi)容 Overview Thin Client Architecture (Server Side Application) Thick Client Architecture (Client Side Application) Medium Cli

2、ent Architecture Distributed ArchitectureOverview The geoprocessing is breaking down into server-side and client-side tasks. A client typically is a Web browser. The server-side consists of a Web Server, Web GIS software and DatabaseOpenGIS Model of portrayal workflowWMS: The portrayal model has fou

3、r tiers The selection process retrieves data from a geospatial data source according to query constraints such a search area or thematic selections The Display Element Generator process turns the selected geospatial data into a sequence of display elements. It attaches styles such as symbols, line s

4、tyle, fill style to spatial features, generates annotation from alphanumeric attributes, sorts the display elements in a certain order and does other graphical processingWMS: The portrayal model has four tiers The Render takes the display elements and generates a rendered map. Example of rendered ma

5、p are In-memory display lists, GIF-files or postscript files The Display process makes the rendered map visible to the user on a suitable display device WMS: Three different types of data Features and coverages (e.g. raster data) retrieve Display elements generated from the Display Element Generator

6、 Images produced by RenderThin Client ArchitectureIn a thin-client system, the clients only have user interfaces to communicate with the server and display the results.All the processing is done on the server actually.The server computers usually have more power than the client, and manage the centr

7、alized resources.The user on the client does not need any knowledge about the linkage of the WMS at the server side, but the system administrator or application developers should be familiar with these techniques.The Picture Case In the Picture Case, what travels across the Internet in response to a

8、 clients request is essentially a picture of a map, such as a GIF, JPEG or PNG image constructed by a Map Server. Major advantages of this model driven from Data base centralization and are: Central control Easy for data updating Keep the latest version Generally cheaper Integration possibilities Re

9、garding some cartographic aspects such as font And disadvantage are: Not responsive to local needs No local accountability Large data volume Response time slow: user use a browser and it take time to download new HTML frame Less interactive: in client side there is limited application and browsers a

10、bilities Vector data does not appear in client side: browsers without additional plug-in can not read vector filesThick Client Architecture The user interface functionality has progress from simple document fetching to more interactive applications.The Data Case the data case provides the ability to

11、 send geographic feature data from the server to the client. GML, SLD Major advantages of this model are: Document/graphics standard are not required Vector data can be used Image quality not restricted to GIF and JPEG Modern interface is possible; it is not restricted to single-click Operations And

12、 disadvantages to Client Side GIS Nonconformance cans limits User base Users require to obtain additional software Platform/browser are incompatibleMedium Client Architecture In the Graphic Element Case, what travels between the web server and the client is a packaged set of individual elements, typ

13、ically already in a projected reference system, and with already defined symbolization for geographic features. SVGDistributed Architecturep The general idea of the distributed GIS service model is that a client program, in either an Internet browser or an independent application, should be able to

14、access the resources distributed in the entire network.p The resources refer to both geodata and geoprocessing components available in the network.p “geodata anywhere, geoprocessing anywhere” model means the geodata and geoprocessing tools could be distributed with the largest flexibility virtually

15、anywhere in the network.p The geodata and geoprocessing components do not have to in the same site, but they should be able to cooperate or integrate whenever they are needed to finish a specific task.characteristic Object oriented（面向?qū)ο螅?Distributed（分布式） Interoperable（互操作）Web Service的定義 A web servic

16、e is a software application or component identified by a URI, whose interfaces and binding are capable of being described by standard XML vocabularies and that supports direct interactions with other software applications or components through the exchange of information that is expressed in terms o

17、f an XML Infoset via Internet-based protocols. /2002/ws/ WebServices 是一個(gè)由URI 指定的軟件組件或應(yīng)用，它的接口和綁定可以用標(biāo)準(zhǔn)的XML進(jìn)行描述并支持與其他軟件和組件進(jìn)行交互。Web Service的特點(diǎn)q WebServices 重要之處在于，WebServices 實(shí)現(xiàn)平臺(tái)的細(xì)節(jié)和業(yè)務(wù)調(diào)用程序無(wú)關(guān)，WebServices形成松散耦合的組件系統(tǒng)q 對(duì)于WebServices 的外部使用者而言，WebServices 是一種部署在Web 上的對(duì)象組件，它具備以下特征：（1）良好的封裝性（2）

18、分布性（3）使用標(biāo)準(zhǔn)協(xié)議（4）跨平臺(tái)、跨語(yǔ)言（5）可集成能力Web Service的特點(diǎn) 從一種軟件系統(tǒng)的觀點(diǎn)來(lái)說(shuō)，由WebServices 來(lái)進(jìn)行集成的系統(tǒng)中，WebServices 還應(yīng)該具有以下特性：（1）WebServices 應(yīng)該是自描述的。（2）WebServices 應(yīng)該是可查找的。（3）WebServices 應(yīng)該是可互操作的。（4）Web 應(yīng)該有普遍性。Catalog Serviceq UDDI(通用描述、發(fā)現(xiàn)和集成)是2000年9月由Ariba、IBM、Microsoft和其他33家公司發(fā)起的業(yè)界標(biāo)準(zhǔn)方法。q UDDI提供下列基本服務(wù) Publish解決Web Servic

19、e提供商如何使用UDDI注冊(cè)自己及其服務(wù) Find解決客戶如何查找所需的Web Service Bind解決客戶如何連接到Web Service，以及如何使用找到Web ServiceService Interoperability stackGeoService 在現(xiàn)有GIS 系統(tǒng)基礎(chǔ)之上，對(duì)已有的數(shù)據(jù)及功能模塊進(jìn)行重新解析、包裝及組合，可以實(shí)現(xiàn)空間信息WebServices，即GeoWebServices。 其基本要素是各個(gè)空間信息的Web 服務(wù)，服務(wù)間數(shù)據(jù)通信采用XML 作為數(shù)據(jù)流的格式，控制通信采用WebService 調(diào)用的方式。 由于分布性與互操作是地理信息系統(tǒng)的必然要求，GeoWebServices 可以說(shuō)正是順應(yīng)了這種要求。 從數(shù)據(jù)共享的角度看 從軟件復(fù)用的角度看 從系統(tǒng)集成的角度看 基于對(duì)象關(guān)系的RPC方法 基于消息中間件的RPC方法 WebService的方法傳統(tǒng)WebGIS vs. GeoServiceOGC: Web S