NVO Summer School 2008 1 VO Protocols and Jargon Overview Tom McGlynn NASA/GSFC THE US NATIONAL VIRTUAL OBSERVATORY
Mar 27, 2015
NVO Summer School 2008 1
VO Protocols and Jargon Overview
Tom McGlynnNASA/GSFC
THE US NATIONAL VIRTUAL OBSERVATORY
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Summary
What are the VO agreements and tools that are used within by VO clients and services?
• Set the context for building blocks that subsequent talks will describe in detail.
• Show how the protocols work together.
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VO Protocols and Jargon
• Data Formats– VOTable– FITS– XML
• Data Access– Cone Search – Simple Image Access (SIA) – Simple Spectral Access (SSA) – Table access/SkyNode
• Astronomical Data Query Language (ADQL)(extends SQL)
• Semantics– Uniform Column Descriptors (UCDs)– Space-Time Coordinates (STC)– IVOA Identifiers
• Registry– Resource Metadata– Registry Protocols– OAI
• VOEvent• NESSSI• VOSpace• PLASTIC/SAMP
Services
• Discovery portal: suite of collaborating tools to find data.– Registry: keyword search interface to registry db– SimpleQuery: Web tool to search and filter tables– Inventory: find data near sets of positions– DataScope: find everything near a given position– VIM: VO Integration and Mining-Combine data from multiple sources– Table converters/wizards– VOClient: Work from the command line.
• NOAO Portal: Graphical interface to VO data• iPortal: Access to VO through mobile devices• TOPCAT: CLI tool to manipulate tables• VOPlot: CLI tool to plot VOTable data• VOStat: Web tool to do statistics of VO data.• WESIX: Web tool to extract and correlated objects from images.• OpenSkyQuery: Web tool to query many on-line tables• WCSFixer: Determine exact geometry of images.
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Formats
• VOTable– XML format for tabular information
• Catalog query results• List of images or spectra• Lists of resources• Includes UCDs for columns
• FITS– Standard astronomical binary data format– Images, spectra, …
• XML (eXtensible Markup Language)– Industry standard– Hierarchical– Extensible
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Data Access:Cone Search
• Simple query around a given region• Returns VOTables
• Examples:
What observations has Spitzer made of the Antennae?
How many x-ray objects are within 30’ of Abell 1656?
Data Access: Simple image access
• What images overlap a given region?
• Create me an image of this region.
• First step produces VOTables with links to image
• User downloads images as FITS in second stage
• V1.0 is widely deployed. V2.0 is under development.
• Examples:Find all Chandra X-ray images near
the Galactic center.Ask SkyView for an I/R cutout of the
Orion spur.
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Data Access: Simple spectral access
• What spectra are available within this region
• More sophisticated than SIA (includes support for Data Models and more complex criteria)
• Some services beginning to appear.
• Examples:Does HST have an FOS
spectrum for this star in this wavelength band?
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Data Access: Table Access Protocol and SkyNodes
• Table Access Protocol– Standardized access to complex
queries of remote tables– Currently under development– Uses ADQL and simpler queries
• SkyNode– SOAP Web-Service based– Sophisticated access to
tables– Supports distributed queries– Uses ADQL– Many operational nodes but
should eventually be subsumed in TAP.
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Query languages
• SQL: Structured query language. Industry standard to generating and extracting information from tables– Widely supported in free and commercial
products (Oracle, Sybase, MySQL, Postgres, …)
• Astonomical Data Query Language (ADQL)– Enhanced version of SQL to support astronomical
queries• Positional correlations• Complex regions on the sky
– Under rapid development
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Semantic content
• IVOA identifiers– Scheme for providing unique identifiers for any thing that
needs to be distinguished. Services, requests, …– ivo://authority/authority_controlled_string#sub-resource– Used in registries and many other protocols
• Resource metadata– Standardized format for the description of a service, data
collection, facility.– XML format based on the Dublin-core metadata descriptions
for published resources.– Used inside registries.
• Uniform Column/Content Descriptors (UCDs)– Standardized names for table columns with relatively high
degree of specificity.– pos.eq.ra or phot.flux;em.ir– Used in VOTables and by Cone search and SIA
• Space/Time Coordinates– Way of specifying points or regions of space-time.– Can be simple or very complex– Used in ADQL and VOEvent
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Discovering Resources
• Registry– Collection of resources that users can find
included Cone Search, SIA, SSA and SkyNodes.
– User access via registry access protocol– Registry-registry communication via OAI.– ‘Publishing’ registries sometimes meant to
be seen only by other registries
• Registry access– How users query the registry– Standard adopted and recently
implemented.
• Open Archive Interface (OAI)– Library community standard– Registry-registry communication to ensure
that all registries are up to date.
• VOEvent– VO protocol for publishing and receiving
notice of transient/urgent events– Describes events using STC
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Access, Control and Communication
• NESSSI– NVO Extensible, Scalable, Secure Service Infrastructure– Provide access to protected resources, especially Grid
computational resources.
• VOSpace– Access to storage resources in a standardized way.– Standard agreed. Some implementations available.– Promotes ‘scripting’ of VO access.
• PLASTIC/SAMP– Platform for Astronomical Task InterCommunication (prototype
protocol)– Simple Application Messaging Protocol (permanent standard)– Applications publish and receive notifications of events from other
applications (e.g., selection of a given object) to enable coordinated actions, e.g. TOPCAT – Aladin
– Many PLASTIC services deployed. SAMP protocol currently under review.
Portals
• NVO Data Discovery Portal: Find and get NVO data quickly.
• NOAO Portal: Visualize relationships of data.
• iPortal: NVO on cellphones and iPods.
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Some popular tools
• WCSFixer: Web interface to correct errors in geometry of image.
• WESIX: Find objects in image then cross-correlate with other catalogs
• TOPCAT: Java based tool to get, manipulate and display tables.
• Aladin: Java based tool to get, manipulate and display images
• VOPlot/VOStat: Plotting and statistics for VOTables
• OpenSkyQuery: Query and cross-correlate many VO datasets
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Miscellaneous Jargon
• Web Service: Web-based application intended for use by programs (possibly in addition to interactive use)
• REST: Representational State Transfer ~ Using stateless interfaces to access Web. Similar to GET based CGI.
• SOAP: Simple Object Access Protocol– Not so simple XML-based method for Web
services.
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How does it work together?
Example:VOEventnet’s use of DataScope to gather
information on recent events:– http://voeventnet.caltech.edu/
• Use first HTML feed to get link to event 323542 (from earlier today)
• Click on View data link.
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Immediate access to data near a recent event using DataScope
• VOTable• FITS• Cone Search Protocol• Simple Image Access (SIA)
Protocol • VO Registry• V OClient• Resource Metadata• Registry Access Protocols• Uniform Column Descriptors
(UCDs)• Space-Time Coordinates (STC)• IVOA Identifiers• VOEvent
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• Event is detected by VOEvent publisher who publishes the event.
• VOEvent notification received by CalTech VOEvent consumer.
• STC position of VO event noted and used to initiate DataScope request at HEASARC.
• DataScope sends request to VO Registry at ST ScI to find appropriate services.
• DataScope sends out Cone and SIA (soon SSA and SkyNode) requests to registered services and gets back VOTables of results.
• SIA VOTables index FITS files• DataScope sends FITS and VOTables to user or other
VO-enabled tools.