scalable metadata definition frameworks raymond plante ncsa/nvo toward an international virtual...

Scalable Metadata Definition FrameworksRaymond Plante

NCSA/NVO

Toward an International Virtual Observatory

How do we encourage a smooth evolution of metadata standardsthat won’t eventually collapse under its own weight?

http://www.us-vo.org/metadata/http://monet.astro.uiuc.edu/~rplante/VO/metadata/fw-draft.ps.gz

Scalable

— the number of metadata terms used by an application environment can grow with a small increase in the cost of supporting them

Metadata Definition Framework

— the standards/conventions for creating and using metadata dictionaries to support interoperable exchange of information

Frameworks

— there are a number of alternative ways to build this framework

http://www.us-vo.org/metadata/

Scalable Metadata Definition Frameworks


Title (string)Definition: A name given to the resource.Comment: Typically, a Title will be a name by which the resource is formally known. Publisher (string)Definition: An entity responsible for making the resource available

Comment: Examples of a Publisher include a person, an organization, or a service.

Creator (string)Definition: An entity primarily responsible for making the content of the resource.Comment: Examples of a Creator include a person, an organization, or a service.

Description (string, free text)Definition: An account of the content of the resource.Comment: Description may include but is not limited to: an abstract, table of contents, reference to a graphical representation of content or a free-text account of the content.

Metadata Dictionaries

encode in XML



Metadata are used in a variety of different contexts

• Resource Description

• Metadata exchange with a serviceform of metadata may be different between query and result

• SQL vs. VOTable

• Data access through a data model

• Semantic analysis to transform metadata from one “basis” to another

• “radio” waveband to 1 – 30 GHz

• converting positions from one system to another

• Data Dictionarytraditionally oriented toward real people (users, developers)



Goals of the framework

• To unify the use of metadata across different contextsensure concept has same meaning/behavior in different contexts

• To clarify how metadata can be bound to various encoding formats and software interfacespossible formats: XML, SQL, UCD

• To provide a manageable framework for extending schemas or creating new ones

complete top-down definition is not necessary

can use multiple schemas in the same application

can correct mistakes later

can create new metadata when necessary

• To enable schema-independent software for using metadata

manageable =



Principles for an Approach• Leverage off of existing standards

key standards: XML Schema, WSDL, & RDF

Leverage ~ ability to use software that complies with these standardsuse standard markup directly when appropriate

allow straightforward, metadata-independent translation

• Partition metadata into small groups of related concepts

• Allow metadata from different schemas to be used in the same application

• Encourage community-based development of metadata standards– provide framework that a standards process can built upon

– don’t stifle localized specialization “outside” a standard

• Re-use of dictionary across different contexts



Re-use of dictionary across different contextsoriginal metadata dictionary can be modified slightly to …

describe a resource or service

configure a client interface



Existing Approaches to Metadata Dictionaries

• XML Schema

• RDF Schema

• DAML (DARPA Agent Markup Language)

• GridForum’s Grid Object Specification (GOS)

• FITS Tables



Components of the Metadata Dictionary

• Identification namespace, version, provenancecontext: definition, resource, service, client

• Syntactic types: new types that can be associated with metadata

• Metadata definitions:name, type, definition, allowed valuessupported operators: numeric: less than, name: last name starts with

• Semantic Relationships• Bindings:

corresponding UCD names, FITS keywords, non-trivial XML mappings

conversion to native metadata schemas

Possible Markup<VOSCHEMA context=“definition” [namespace attributes…] > <PROVENENCE> <!–- identification of responsible organization/individual --> <!–- identification of version/revision --> </PROVENANCE>

<TYPES> <!–- declare new XSD types or import them from other files --> </TYPES>

<DICTIONARY> <ELEMENT name=“Antenna” type=“integer”> <ANNOTATION> <DEFINITION xml:lang=“en”> The identifying number for the inteferometer antenna </DEFINITION> <TIPS> <TIP role=“implementer” xml:lang=“en”>...</TIP> </TIPS> </ANNOTATION>

<VALUES>  </VALUES>

<OPERATORS>  </OPERATORS> </ELEMENT>

</DICTIONARY>

<SEMANTICS>  </SEMANTICS>

<BINDINGS> <!- - This section would contain markup describing how the metadata can be rendered in some encoding scheme. In particular, conversions to native metadata schemas would be described here. --> </BINDINGS>

</VOSCHEMA>



Example Uses

• Publishing Metadata Schemasused to define metadata and operators independent of any application

standard stylesheets make it easy to produce human readable form

• Metadata Standards Developmentconformant dictionaries can be prototype using standard software

structured format aids review by standards body (style guidelines)

• Resource Descriptionoriginal definition serves as template for describing a resource

e.g. curator modifies range of metadata values to match coverage of resource

• Service Description: search serviceuse markup describe queryable columns and their ranges

allows portals to make intelligent decisions about when/how to query a resource

• Metadata access via Data Access Layerautomatic source code generation for interfaces to metadata

context=“definition”

context=“resource”

context=“service”



Example Uses• Client Configuration

dictionary used to create user interfaces on-the-fly (without new programming)

context=“client”

FlexQuery searchclient

terms from 4different schema

interface tosearch operatorsgenerated automaticallyfrom metadatadefinition

scalable metadata definition frameworks raymond plante ncsa/nvo toward an international virtual...

Documents