1. Scalable Metadata Definition Frameworks Raymond Plante NCSA/NVO Toward an International Virtual Observatory How do we encourage a smooth evolution of metadata standards that 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

2. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory 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

3. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Metadata are used in a variety of different contexts Resource Description Metadata exchange with a service form 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 Dictionary traditionally oriented toward real people (users, developers)

4. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Goals of the framework To unify the use of metadata across different contexts ensure concept has same meaning/behavior in different contexts To clarify how metadata can be bound to various encoding formats and software interfaces possible 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 =

5. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Principles for an Approach Leverage off of existing standards key standards: XML Schema, WSDL, & RDF Leverage ~ ability to use software that complies with these standards use 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

6. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Re-use of dictionary across different contexts original metadata dictionary can be modified slightly to … describe a resource or service configure a client interface

7. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Existing Approaches to Metadata Dictionaries XML Schema RDF Schema DAML (DARPA Agent Markup Language) GridForum’s Grid Object Specification (GOS) FITS Tables

8. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Components of the Metadata Dictionary Identification namespace, version, provenance context: definition, resource, service, client Syntactic types: new types that can be associated with metadata Metadata definitions: name, type, definition, allowed values supported 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

9. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Possible Markup The identifying number for the inteferometer antenna...

10. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory <!-- semantic relationships between the metadata defined here and those defined elsewhere can be put here --> <!- - 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. -->

11. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Example Uses Publishing Metadata Schemas used to define metadata and operators independent of any application standard stylesheets make it easy to produce human readable form Metadata Standards Development conformant dictionaries can be prototype using standard software structured format aids review by standards body (style guidelines) Resource Description original definition serves as template for describing a resource e.g. curator modifies range of metadata values to match coverage of resource Service Description: search service use 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 Layer automatic source code generation for interfaces to metadata context=“definition” context=“resource” context=“service”

12. Scalable Metadata Definition Frameworks Toward an International Virtual Observatory Example Uses Client Configuration dictionary used to create user interfaces on-the-fly (without new programming) context=“client” FlexQuery search client terms from 4 different schema interface to search operators generated automatically from metadata definition