Prototype for Wrapping and Visualising Geo- Referenced Data in Distributed Environment using XML

Transcription

1 Prototype for Wrapping and Visualising Geo- Referenced Data in Distributed Environment using XML Jianting Zhang Muhammad S. Javed Amir Shaheen Le Gruenwald School of Computer Science The University of Oklahoma 11/09/2000

2 Overview: Introduction Motivation Objectives Why XML? Related Work System Implementation System Architecture GeoXML Generation & Parsing Wrapping GRI (Geo-Referenced Information) from Flat File to GeoXML Document Building GeoXML Mediator Client GRI Visualization Experiments and Results

3 Motivation Most of existing web-based mapping systems adopt twotier architecture. Personal geo-referenced information will be overwhelming in the near future. Global Positing System (GPS) Cellular Phone, etc. Pattern of GRI Usage in the future Users integrate thematic GRI with basic GRI. Data vendors provide basic GRI.

4 Objectives Developing a three-layer XML based architecture that allows flexible web databases integration. Integrating geo-referenced information from distributed and heterogeneous web sites that provide geo-referenced information. Visualizing integrated geo-referenced information for better understanding and decision-making.

5 Why XML Platform Independence Data format Independence Application Independence More efficiency in dealing with semi-structured data, such as GRI

6 Related Work Ref GRI XML Wrapping Integrating Visualization (Amann, 1999) Yes Yes (SGML) Yes (Baru, 1999) Yes Yes Yes Yes (Ciancarini, 1999) Yes Yes (Shimada, 1999) Yes Yes Yes (Sorokine, 1998) Yes Yes (Thiran, 1999) This Study Yes Yes Yes Yes Yes Yes

7 System Architecture Client: Client: Visualization by by Java Java Applet Applet GeoXML Mediator Server: Server: XML XML document integration(dom) GeoXML Distributed GRI GRI Wrapper(s): Servlet Servlet Programming Distributed Data Server for OODB, e.g. Objectivity Distributed Distributed Data Data Server Server for for Flat Flat File, File, e.g. e.g. ESRI ESRI Shape Shape File File Distributed Data Server for RDB, e.g. ORACLE

8 XML Generation and Parsing SAX (Simple API for XML) Techniques First-in-first-out (Sequential Processing) Predefined call back functions: startdocument(), enddocument(), startelement(), endelement() and characters(). DOM: (Document Object Model) Tree Structure : maintaining hierarchy & Random Access APIs: createelement(), createattribute(), setnameditem(), appendchild(), write ()

9 GeoXML DTD (Document Type Definition) <!ELEMENT Point (CList)> <!ATTLIST Point name CDATA #REQUIRED> <!ELEMENT PolyLine (CList)> <!ATTLIST PolyLine name CDATA #REQUIRED> <!ELEMENT Polygon (CList)> <!ATTLIST Polygon name CDATA #REQUIRED> <!ELEMENT CList (#PCDATA)>

10 Mapping GeoXML to Java Classes public interface AbstractShape { public abstract int getshapetype(); } public class GRIPoint implements AbstractShape { double x,y; public GRIPoint(double x,double y); public double getx(); public double gety(); }; public class GRIPolyline implements AbstractShape { Vector xx,yy; public GRIPolyline() public void addpoint(double x,double y); public double [] getxx(); public double [] getyy(); }

11 GeoXML Wrapper From Flat File Create New XML Document Get the Number(num) of Geo-objects from flat file by calling ShapeFile API For I= 1 to num Switch type: Point Polyline Polylgon CreateElment(Point) CreateElment (Polyline ) CreateElment (Polygon ) CreateAttribute CreateAttribute CreateAttribute CreateElement (CList) CreateElement (CList) CreateElement (CList) Transfer coordination value into string Append Node to XML File Output the Generated XML Document

12 Mediator Server for GeoXML Integration Get Parameters from client request Meta Layers Combination Retrieve Meta Data from ORACLE database Generate XML file from Meta Database Get Meta data for all requested layers For each requested layer Send request to distributed wrapper server Parse returned XML into a vector Vector Combination Generate XML file from the vector Return to Client

13 Client Side Visualization Layer Selection (a Servlet) Dynamic HTML page generation with a Visualization Applet in it. Visualization Interface Rendering Zoom in Zoom Out Full Extent Communicate with the Mediator Server Get Integrated XML Document XML Parsing Accept User Visualization requests

14 Data Used in the Experiments LAYER No. 0 EXP. 1 (World) CITIES(Point) EXP. 2 (Cleavland,OK,USA) PLACES (Point) 1 2 RIVERS (Polyline) COUNTRIES (Polygon) RIVERS (Polyline) CENSUS TRACKS (Polygon)

15 URLS for the experiments 1. Retrieving a Geo-XML document from a wrapper 2. Retrieving meta data from Mediator Server *3. Retrieving integrated XML data: 4. Setting Layer combinations 5. Client Side Visualization:

16 Retrieving GeoXML from a Wrapper

17 Setting Layer combinations

18 Visualization of Integrated GRI

19 Visualization with Zoom In Box

20 Zoomed GRI showing detailed information

21 Accomplishment OPENESS: Any application that supports XML can make use of the wrapped GRI and integrate it into other systems. INTEGRATION: Using three-tier architecture and mediator, virtual GRI website can be built to provide integrated GRI Services. VISUALIZATION: Help people understand Georeferenced information better and make better decisions.

22 Future Directions Adding more features to WRAPPER. Returning a part of data instead of the whole dataset upon user request. Adding more features to MEDIATOR. Complex query support based on XML. Spatial and attribute indexing. Adding more features to VISULIZATION. Pan, Identify, Hyperlink. Color/Size/Pattern selection. Layer/Object sequence selection, etc.