• Global Astrophysics Data Resources Loosely Connected By the Internet
• Observational data archives or repositories
• Derived data products (astronomical catalogs, browse images, video)
• Data analysis packages
• Visualization/presentation packages
• Special services (bibliography, discipline-specific knowledge bases, directories)
• Distributed Storage, Processing, and Management
• Multispectral surveys (Data volume ~ terabytes)
• Islands of Information?

• Current (connections via hyperlinks): one to one
• Near Future (connections to multiple DBs all at once, via middleware): one to many
• Long Term (multiple inter-connectivity, federated databases): many to many
• Distributed Autonomous data centers
• Intelligent Agents
• User-defined Profiles and _Preferences
• Access via Multiple Interfaces

• Integrated search and discovery
• URL Registry (e.g., Yellow Pages, GLU, AstroBrowse)
• Query processor (e.g., AMASE, ISAIA)
• Browsing/visualization to support selection (ADC Data Viewer, AEQ)
• Batch queries (Feed output stream of one data service to another)
• Tools to support integration of results
• Data and software exchange
• FTP of data and software updates (pull)
• Download of Browser Plug-in (pull)
• Automated Updates (HST DB replication) (push)
• Hybrid Techniques (with data cache or aircache) (push & pull)
• Packaging of software with data (XDF)

• Data volume and network bandwidth
• Cache of pre-computed results (e.g., astronomical catalogs)
• Data filtering at data site, ship results only
• Deployment of user code (platform independent S/W)
• Data visualization for exploration and selection
• Registration, Sensitivity, Positional Accuracy
• Coordinate transformation on a large scale
• Calibration and normalization
• Query Optimization across Multiple Sites
• Query execution plan for efficient cross-correlation
• Indexing for fast access

• Content-based Searches
• Science goal driven queries instead of SQL
• Data Understanding (Domain Context)
• Human Interface —> S/W Mapping —> Object-oriented Mapping
• Data Annotation for Correct Interpretation
• Measured parameters, units, quality, range of validity
• Algorithm and calibration used, pedigree
• Theoretical models applied
• Data Organization
• File directory structure
• Database schema

• Syntax
• Directory Structure
• Size, Format, Location, URL
• Semantics
• Usage Convention (e.g., FITS)
• Extensible Standards to Encompass Different Disciplines (DTD, XML)
• Astronomical Nomenclature and Designation
• Conceptual Data Model
• Metadata Language or Representation
• FITS, ASCII, IEEE Binary
• Astronomical XML

Aspects of Metadata Usage

• Search, browse, retrieval (Human)
• Data extraction and interpretation
• Navigate among services
• Ingest, quality assurance, (re-)processing
• Science product generation pipeline
• Content analysis
• Storage, archive (Data Management)
• Information relevant for effective system design and operation
• Application to application transfer (Machine)
• Enable "context" interchange (distributed queries and transformations)

• Interface Standards for Software Tools
• Tools for Schema Mapping
• Document logical structure of database (key elements and relationship)
• Mapping of local definitions into common terminology
• Track changes and updates at other sites
• Tools for Data Integration and Fusion
• Dynamic Interface with user preferences
• Intelligent Software Agents to mediate interaction