September 7, 2005NVO Summer School 1

Building a SkyNode Server

Tom McGlynnNASA/GSFC

THE US NATIONAL VIRTUAL OBSERVATORY

September 7, 2005NVO Summer School 2

Why are SkyNodes hard?

• Inherently distributed:– SkyPortal-SkyNode-SkyRegistry

• Need to handle complex XML input– XML version of ADQL– Execution Plans

• Setting in Servlet container environment– Big learning curve in getting started

• Lack of defining documentation– IVOA document is primarily requirements– WSDL does not encode semantics

• If you use SQLServer take a long look at using the JHU implementation (also needs Mono or .Net)

September 7, 2005NVO Summer School 3

What do you need for a SkyNode?

• A database to query– In principle this doesn’t need to be

relational but in practice it will be!

• A Web site to place the SkyNode– But not behind firewall or NAT server

• Makes demoing in SS hard• NOAO accounts available for people who need

accounts

September 7, 2005NVO Summer School 4

How do SkyNodes Work

September 7, 2005NVO Summer School 5

What does a SkyNode need to do?

• Metadata:– WSDL request– Various configuration paramters

• Tables, columns, supported formats

• Simple Query• Cost estimate for Query

– Number of rows query would return

• Execution plan

September 7, 2005NVO Summer School 6

Handling an Execution plan

• Find the appropriate node• Are there further nodes?

– Relay the plan to that node– Ingest the results into a temporary table

• Run the query on the local node• Format the results in a VOTable

September 7, 2005NVO Summer School 7

How do we do the query?

• Translate ADQL/x to ADQL/s• Transform REGION (see HTML)• Transform XMATCH (see HTML)• Handle local database peculiarities

– TOP– Creating temporary tables– Handling of Dec columns

September 7, 2005NVO Summer School 8

FullSkyNode Library

• Replaces earlier summer school libraries– Not yet rock solid but working on it...

• Runs as CGI– Do not need AXIS or TOMCAT

• Uses Java JDBC library to communicate with database.

• Uses extremely simplified VOTable parsing and generation.

• Uses built-in XSLT capabilities in Java 1.5 to generate ADQL string

September 7, 2005NVO Summer School 9

Additional Prerequisites

• Uses Perl wrapper script• Table is assumed to have RA and Dec

columns in decimal degrees.

September 7, 2005NVO Summer School 10

Status

• Supports all SkyNode functionality except getAvailability metafunction.

• Tested on Sybase and MySQL databases.• Supports REGION and XMATCH• Easily configured.• Fails poorly – errors not well propogated

to SkyNode.• Not all database dependencies are likely

uncovered.

September 7, 2005NVO Summer School 11

Configuration: vo.settings

TargetNode=TSTHSRC3TableName=spocs,spocs_ext note no space.

tabledesc=SPOCS Table, SPOCS Extension tableSize=-1,-1 jdbcURL=jdbc:mysql://localhost/SPOCSposituncert=10 tableweight=1.e9jdbcName=skynodejdbcPwd=nvo wsdlFile=skynode.wsdl

September 7, 2005NVO Summer School 12

What’s next

• Further enchancements and robustifications.

• Easily modified to handle tables with only Galactic coordinates or other formats

• Easy to disable functionality if you don’t want to be full sky node.

• Should be able to support developing SkyNodes in student projects.