14 Apr 2005

VOEvent workshop 1

XML Schema and the VO Registry

Matthew J. GrahamCACR/Caltech

THE US NATIONAL VIRTUAL OBSERVATORY

14 Apr 2005

VOEvent workshop 2

Overview: the five Ws

• What is an astronomical resource?• How is an astronomical resource

described?• Where do such descriptions reside?• Why are such descriptions needed?• When are such descriptions used?

14 Apr 2005

VOEvent workshop 3

VOResource: Core

• Type• Title• Short name• Identifier• Curation:

– publisher – date– creator – version– contributor – contact

• Content:– subject – type– description – content level– source – relationship

14 Apr 2005

VOEvent workshop 4

VOResource: Extensions

• Organisation• Registry• Authority• Data Collection:

– coverage – format – rights• Service:

– interface: ParamHTTP, WebService, GLUService– SkyService:

• TabularSkyService: ConeSearch, SimpleImageAccess, OpenSkyNode

– CEAService• CEA Application

14 Apr 2005

VOEvent workshop 5

Extension models: substitution groups

• Schema:<xs:element name=“Interface” substitutionGroup=“interface”><xs:element name=“WebService” substitutionGroup=“interface”><xs:element name=“ParamHTTP” substitutionGroup=“interface”><xs:element name=“Service”>

<xs:complexType><xs:sequence>

<xs:element ref=“Interface”/>

• Instance:<Service> <Service> <Service> <Interface> <WebService> <ParamHTTP>

14 Apr 2005

VOEvent workshop 6

Extension models: xsi:type

• Schema:<xs:complexType name=“Interface”><xs:complexType name=“WebService”>

<xs:complexContent><xs:extension base=“Interface”>

<xs:complexType name=“ParamHTTP”><xs:complexContent>

<xs:extension base=“Interface”><xs:element name=“Service”>

<xs:complexType><xs:sequence>

<xs:element name=“…” type=“Interface”/>

• Instance:<Service> <Service> <Service> <… xsi:type=“Interface”> <… xsi:type=“WebService”> <…

xsi:type=“ParamHTTP”>

14 Apr 2005

VOEvent workshop 7

The registry

• A store for VOResource records (documents)• Functionally equivalent to UDDI • Records are published into a publishing registry,

typically by interactive web form• Registries can be harvested via OAI interface:

– Identify – ListIdentifiers– ListSets – ListRecords– ListMetadataFormats – GetRecord

• Records can always be expressed in Dublin Core format

• Registries can be queried by basic text search and ADQL/XQuery

14 Apr 2005

VOEvent workshop 8

Registry implementations

Registry Store type Publishing

Searchable

Harvesting

Handle extensions

Caltech Native XML Yes Yes Yes Yes

StSCI Relational Yes Yes Yes Partially

NCSA Filesystem Yes Yes No No

HEASARC Filesystem? No No No No

Astrogrid Native XML Yes Yes Yes Yes: CEA

Galahad Native XML? Yes Yes Yes Yes: CEA

CDS Relational? No Yes No No

JVO ? No ? Yes? Partially: OpenSkyNodeJ

+ CfA, ESO, ESAC, AusVO, …

14 Apr 2005

VOEvent workshop 9

Interoperability problems

• Namespaces• Versioning• Incomplete records• Wrong records• Missing records• Validation

14 Apr 2005

VOEvent workshop 10

Using schema: registry experiences

• Validation• Code binding: JAXB, Castor

– Conflict with W3C XML Schema datatypes– Infinite loops (VOTable)– Marshalling/unmarshalling problems– Performance

• XSLT– A schema is just an XML document

• WSDL– Specify the schema?

14 Apr 2005

VOEvent workshop 11

Using registries: user experiences

• Who uses the registry?– Human vs. computer

• How is the registry used?– Interface functionality

• Why is the registry used?– Too much metadata?

14 Apr 2005

VOEvent workshop 12

Thoughts on VOEvent

• Schema:– Equivalent of RM document– Straightforward but comprehensive– Core + extensions for specialisations– Based on RTML + STC

• Ontology– Necessary for querying and filters

• Registry– VO Registry + subscriber interface