Building a SkyNode Server

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THE US NATIONAL VIRTUAL OBSERVATORY
Building a SkyNode Server
Tom McGlynn NASA/GSFC
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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)

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What do you need for a SkyNode?

• A database to query
• In principle this doesnt 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

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How do SkyNodes Work
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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

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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

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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

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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

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Additional Prerequisites

• Uses Perl wrapper script
• Table is assumed to have RA and Dec columns in
  decimal degrees.

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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.

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Configuration vo.settings
TargetNodeTSTHSRC3 TableNamespocs,spocs_ext
note no space. tabledescSPOCS Table, SPOCS
Extension tableSize-1,-1 jdbcURLjdbcmysql//l
ocalhost/SPOCS posituncert10 tableweight1.e9 jd
bcNameskynode jdbcPwdnvo wsdlFileskynode.wsdl
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Whats next

• Further enchancements and robustifications.
• Easily modified to handle tables with only
  Galactic coordinates or other formats
• Easy to disable functionality if you dont want
  to be full sky node.
• Should be able to support developing SkyNodes in
  student projects.