1. 2004/12/02Slide Number 1 of 15 Exposure Time Calculator (ETC) as a Web Service Donald McLean 2004 Technology Open House

2. 2004/12/02Slide Number 2 of 15 Exposure Time Calculator (ETC) as a Web Service What is a Web Service? Why would the ETC be a good candidate for conversion to a web service? What are some possible uses of an ETC web service?

3. 2004/12/02Slide Number 3 of 15 What is a Web Service? A server that can communicate via a standardized XML messaging system Web services protocols are intended to be platform independent Most implementations are either Java or.Net based Vast variety of vendors, all muddying the waters with different implementations Responsible for generating dizzying numbers of new buzzwords

4. …But What Does That Mean? Web services are a new model of distributed computing Web services are mainly for use by other applications –A repair shop ticket system could use a web service of its parts supplier to automatically order needed parts 2004/12/02Slide Number 4 of 15

5. Web Services Architecture Service Requestor Service Provider Discovery Agency Publish Service Description Find Interacts For more information: http://www.w3.org/TR/ws-arch/ 2004/12/02Slide Number 5 of 15

6. Standards Four standards define the critical elements of web services: –Simple Object Access Protocol (SOAP) describes handshaking with server –Extensible Markup Language (XML) describes format of the request and response –Web Service Definition Language (WSDL) allows servers to describe services being offered –Universal Description, Discovery, and Integration (UDDI) Protocol for listing services in a directory 2004/12/02Slide Number 6 of 15

7. ETC Previously a Java application, part of Scientists Expert Assistant (SEA) project Tomcat web servlet application Mostly Java uses external “SYNPHOT” for some key calculations 2004/12/02Slide Number 7 of 15

8. Why A Web Application? Cultural –Existing ETCs were web applications Performance of desktop application –Communication with remote SYNPHOT server was a serious weakness –Older computers could be frustratingly slow 2004/12/02Slide Number 8 of 15

9. Why Not An Application? Original implementation (remote SYNPHOT) slow and problem prone Local SYNPHOT with remote files worse –No Windows version of SYNPHOT Local SYNPHOT with local files –Still no Windows version of SYNPHOT –Huge (500MB) data library –Data library must be kept up-to-date Internet connection is more or less required 2004/12/02Slide Number 9 of 15

10. Why A Web Service? ETC already uses XML –Log of each request Used in testing and debugging –Log of each result Used to render result page Used to render previous result page Can throw hardware at performance 2004/12/02Slide Number 10 of 15

11. ETC As Web Application User HTTP Get Request XML Request Log ETC Servlet Request Local SYNPHOT HTML Response XML Response Tomcat Web Server ETC Library Response 2004/12/02Slide Number 11 of 15

12. Adding Web Service User HTTP Get Request ETC Servlet Request Local SYNPHOT HTML Response Tomcat Web Server + WS Extensions ETC Library Response External Application XML Request ETC Web Service Request XML ResponseResponse 2004/12/02Slide Number 12 of 15 XML Request Log XML Response

13. Possible Use: APT Integration The original SEA had an integrated ETC One cycle 13/phase 1 comment requested access to the ETC from within APT APT and VTT use network interfaces to access other services Tools could be designed to run multiple scenarios (another cycle 13/phase 1 comment) APT users would need to supply information not currently needed 2004/12/02Slide Number 13 of 15

14. Possible Use: VO Search Tool Calculate limiting magnitude of an image See Voisin et al, “Simulating Instruments For Mining Uncalibrated Archives”, in Optimizing Scientific Return for Astronomy through Information Technologies, edited by Peter J. Quinn, Alan Bridger, Proceedings of SPIE Vol. 5493 (SPIE, Bellingham, WA, 2004) pp 294-301 2004/12/02Slide Number 14 of 15

15. Other Uses Available to any application that supports WSDL translation Web services are an “enabling technology” that make it possible for applications to be used in ways not imagined by their designers 2004/12/02Slide Number 15 of 15