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.