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Discovering Geospatial Data Resources via Clearinghouse

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Discovering Geospatial Data Resources via Clearinghouse ... Community list of 'registered' data collections managed and reflected as ... Catalog Services for OGC ... – PowerPoint PPT presentation

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Title: Discovering Geospatial Data Resources via Clearinghouse


1
Discovering Geospatial Data Resources via
Clearinghouse
  • Lessons learned through a passing familiarity
    with Z39.50
  • Doug Nebert, FGDC

2
Clearinghouse expectations
  • Standard fields and operators for discovery and
    display of data
  • Distributed data and metadata resources
  • Search engine capabilities on full-text and
    fields
  • Delivery of structured documents in consistent
    form

3
Standard fields and operators
  • Ability for information provider to support well
    known semantics of fields in search
  • Support for internationalization
  • Allow custom approaches to data management and
    schema, but hidden from the end-user

4
Distributed data and metadata
  • Data and metadata are better managed locally
    rather than centrally
  • Centralized index is a significant investment
    with likely synchronization problems
  • Community list of registered data collections
    managed and reflected as Internet resource for
    distributed query

5
Search engine capabilities
  • Descriptive properties need to be made quickly
    searchable
  • Properties are stored as full-text, text, and
    numeric
  • Multiple properties can be combined with and
    and or boolean operators
  • May be local or remote

6
Structured results
  • For comparison of results from different sources,
    it is desirable to present the results in
    consistent ways
  • HTML, SGML, and text formats supported
  • Well-known subsets of data elements can be
    selected for delivery Brief, Summary, or Full
    are examples

7
More basics
  • Properties are typically aggregated to the
    dataset level for discovery and presentation,
    for distinct data products
  • Some properties are pertinent to collections of
    data products (series, collections, flightlines)
  • Specific properties may vary across a collection
    (pub date, footprint)

8
Data Management may be via
  • A database management application separate from
    the data resource
  • An index of structured information not in a
    conventional DBMS
  • Properties of spatial data managed with and
    within the geodata management system

9
A discovery view
Registry
User
Node
10
A discovery view
Registry
?
Query
User
Node
11
A discovery view
Registry
?
Query
User
Node
12
A discovery view
Registry
?
Query
User
Node
13
A discovery view
Registry
?
Response
User
Node
14
A discovery view
Registry
Data Connections
User
Node
15
NSDI Clearinghouse
  • Uses list of servers registry
  • Provides redundant WWW-Z39.50 protocol gateways
    with server list
  • Returns Brief, Summary, or Full metadata
    reports to client
  • Query of 50 servers becoming difficult
  • Pre-emptive search under consideration

16
Canada CEONet
  • Uses same Z39.50 protocol and FGDC field
    terminology
  • Requires trader-like WWW-Z39.50 gateway for all
    queries
  • Allows terminal descriptions to map to FGDC
    properties in non-standard formats

17
CEOS (NASA/ESA/NASDA)
  • Catalogue Interoperability Profile (CIP) also
    uses Z39.50 and WWW
  • Requires DCE middleware to support query routing
    and ordering
  • Requires intentional search of collections
    information then subordinate search (no product
    inventory search)

18
Scalability of Services
  • Discovery needs to occur as if via DNS
  • Multiple registries will exist, multiple
    communities may define servicespace
  • Gateways for WWW-??? protocols can be bottlenecks
  • Arbitrated queries via trader should be
    permitted, not required

19
Catalog Services for OGC
  • Should support a single common abstract query
    interface to data set properties
  • Should evaluate interfaces in terms of
    interoperability among CORBA, COM, SQL, and WWW
    implementations
  • Should support common properties and community
    differentiation and extension

20
Interactions
  • User/client interacts with a registry/ referral
    server and with data servers
  • Registry/referral server interacts with user and
    data servers
  • Data servers interact with users and forward
    information to registry/referral servers

21
Technology suggestions
  • Z39.50 ISO 23950 Search and Retrieve
  • X.500 or LDAP for aggregate properties
  • Whois for referral service
  • Uniform Resource Characteristics (URC)
  • PICS-NG ratings/metadata service
  • Extensible Markup Language (XML)
  • Resource Description Framework

22
Feature-Level Metadata
23
Hierarchies of Metadata
  • Properties are most often associated with the
    data set or minimum collection of features
    available for acquisition
  • How are feature-level properties exposed to
    search?
  • How are multi-level properties presented to the
    user?

24
One multi-level approach
  • An arbitrary set of features is associated with
    one or more properties via a unique identifier
  • Permits inheritance of properties from multiple
    sources
  • Requires a supplements or supercedes
    condition where a parent case exists

25
National Hydro Dataset
USGS DLG
EPA RF3
General Case
A
B
Basin- Specific
Quad- Specific
Supplemental
Aa
Bb
Feature-list Associations
5
1
2
3
4
4023 Bb 2,3,4,5 4024 Aa 1,2,3
26
Feature Addition and Update
USGS DLG
EPA RF3
General Case
A
B
Basin- Specific
Quad- Specific
Supplemental
Aa
Bb
4023 Bb 2,3,4,5 4024 Aa 1,2,3 4025 C
6 4026 D-b 5
5
1
2
3
4
New Feature
6
Update
C
D
27
Issues
  • Packaging and presentation of linked and
    supplemental metadata
  • Processing of updates to features and propagation
    of metadata over data lifecycle
  • Feasibility in existing data management systems,
    software, and schema
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