ACHIEVING SEMANTIC INTEROPERABILITY WITH HYDROLOGIC ONTOLOGIES FOR THE WEB

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ACHIEVING SEMANTIC INTEROPERABILITY WITH
HYDROLOGIC ONTOLOGIES FOR THE WEB
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6th International Conference on HydroScience
and Engineering
Michael Piasecki Luis Bermudez
Drexel University, College of Engineering
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Content

• Overview of metadata
• Metadata Interoperability problems
• A possible Solution Hydrologic
  Ontologies for the Web

Drexel University, College of Engineering
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Metadata

• Answers what, when, where, how, who
  and why of the described data.
• Helps to discover, access, evaluate and
  use of data.

Metadata
Creator USGS
Keyword Gage Height
Drexel University, College of Engineering
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Hydrologic Information Communities (HIC) need a
metadata agreement
What descriptors can be used ?
Which possible values?
Gage height or water elevation
Keyword or topic
Keyword or topic
Author or Creator
Author or Creator
Is there any metadata agreement available to
describe hydrologic data ?
Drexel University, College of Engineering
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Metadata Specifications related to Hydrology

• ISO-191152003
• FGDC-STD-001-1998
• Ecological Markup Language
• Geographical Markup Language
• USGS Hydrologic Markup Language
• Earth Science Markup Language
• Dublin Core Metadata Initiative

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Problem 1 Metadata specifications lack
domain specific elements

• For example
• They do not tell if area and outlet location
  should be defined when a watershed is being
  described
• For example
• They do not incorporate a list of possible
  stations and variables related to surface
  water collected by a particular HIC
• What is the problem with these ?

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HIC A creates an HTML form to collect Metadata
EX_GeographicIdentifier geographicIdentifier
MD_Identifier code Descriptive
Keywords MD_Keywords
keyword Citation
X
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Not consistent
Water elev.
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Need to incorporate domain vocabulary to get
consistent metadata
EX_GeographicIdentifier geographicIdentifier
MD_Identifier code Descriptive
Keywords MD_Keywords
keyword Citation
consistent
consistent
Drexel University, College of Engineering
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Problem 2 Metadata standards do not solve
Semantic heterogeneities
search for Stage Height
Metadata (ISO) about dataset X keyword Stage
Height thesaurusName GCMD
Metadata (FGDC) about dataset Y Theme_Keyword
Gage Height Theme_Keyword_Thesaurus USGS
Finds only data set X
and not data set Y
Metadata repository
Drexel University, College of Engineering
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Possible solutions to our Problems How to
incorporate domain vocabulary in metadata
specifications?

• Create a new metadata specification.

• Rewrite a previous one and extend

• Hardcode semantics into application

?

• Dynamic Extension with ontologies

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Extending Metadata Specifications to meet
specific needs of a HIC
Express metadata specifications and vocabularies
in ontologies. Use the knowledge inference
capabilities of ontologies to link the metadata
elements with selected vocabulary terms.
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Ontologies Specification of conceptualizations
Example 1. Properties of real world objects are
identified. 2. Similarities are identified. 3.
Concepts are created 4. and are expressed as a
class. 5. Classes are related.
Is inland body
Has a defined channel
Has water
Body of Water
Class
Subclass
River
Lake
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Web Ontology Language OWL
ltXMLgt
W3C Recommendation since 02/2004
Body of Water
River
Lake
lt/XMLgt
ltowlClassgtBody_of_Waterlt/owlClassgt ltowlClassgtRi
verlt/owlClassgt ltowlClassgtLakelt/owlClassgt
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Metadata specs expressed in ontologies
ltXMLgt
Classes
object Properties
datatype Properties
MD_Metadata
fileIdentifier0..1 CharacterString
language0..1 CharacterString
identificationInfo 1..
MD_Identification
abstract CharacterString
lt/XMLgt
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ltXMLgt
Class
Hydrologic Unit
Subclasses
lt/XMLgt
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More about knowledge Inference
Y
ltStation rdfIDA"gt lt/Stationgt ltStation
rdfIDB"gt lt/Stationgt ltStation rdfIDC"gt
lt/Stationgt
ltisPartOf rdfresourceW/gt ltisPartOf
rdfresourceW/gt ltisPartOf
rdfresourceY/gt
W
How to infer the stations that are only in W ?
Program infer
ltowlClass rdfID W-Station type of station
that has property isPartOf W
lt/owlClassgt
W-Stations A, B
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Dynamic extension with ontologies
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e.g. Restrict the descriptor code to only have
W-station values
Dynamic HTML form using the extension
Program could infer
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Ontologies provide means to resolve Semantic
Heterogeneities
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Use of ontologies to map metadata specifications
ltowlClass rdfID "isoMD_Keywords"gt ltowlequi
valentClass rdfresource "fgdcKeywords"/gt lt/
owlClassgt ltowlDatatypeProperty rdfID
"isotitle"gt ltowlequivalentProperty
rdfresource "fgdctitle/gt ltowlDatatypePro
pertygt
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Use of ontologies to solve semantic
heterogeneities among different domain
vocabularies
ltgcmdVariable "gcmdStage_Height"gt
ltowlsameAs rdfresourcenoaastage"/gt
ltowlsameAs rdfresourceusgsgage_Height"/gt
ltowldifferentFrom
rdfresourceeventsStage_Height"/gt
lt/gcmdVariablegt
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Semantic Interoperability
e.g. search for Stage Height
Finds data set X and Y
Metadata repository
Drexel University, College of Engineering
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Why is XML Schema not good enough?
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XML Schema cannot express semantics.
E.g. defining that a watershed has only one
outlet location and only one unique identifier
..ltxsdelement ref"watershed"
type"watershedType" /gt ltxsdcomplexType
name"watershedType"gt ltxsdsequencegt
ltxsdelement ref"outletLoc
type"xsdnonNegativeInteger
minOccurs"1" maxOccurs"1/gt
ltxsdelement refid"
type"xsdnonNegativeInteger minOccurs"1"
maxOccurs"1"/gt
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XML Schema cannot express semantics
ltwatershedgt ltoutletLocgt567lt/outletLocgt
ltnamegtXlt/namegt ltidgt101lt/idgt lt/watershedgt
ltwatershedgt ltoutletLocgt838lt/outletLocgt
ltnamegtXlt/namegt ltidgt101lt/idgt lt/watershedgt
?
?
Valid XML document
Valid XML document
X
Semantically they are not correct 567 ltgt 838
XML Schema is good to validate the structure of a
document, but not the semantics
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Hydrologic Ontologies will help to

• Extend standards
• Solve semantic heterogeneities
• Interoperate between systems
• e.g. Find a numerical model and data to compute
  runoff for a specific location with a specific
  resolution.
• System Engineering benefits
• Efforts are not duplicated because the conceptual
  models could be reused and shared.
• Semantics not need to be hard coded in computer
  programs.

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Acknowledgements
Drexel Team (Luis Bermudez, Saiful Islam, Bora
Beran) Stephane Fellah (Member ISO TC 211 Canada
team) will submit 19115 in OWL to ISO as a draft
document NOPP NAG 13 0040 (Web based
dissemination portal) NSF- GEO Directorate grant
from EAR division to create Hydrologic Metadata
for CUAHSI, prototype Hydrologic Information
System (HIS), in the Neuse River Basin
Discussion List Protégé, Jena, W3C
Drexel University, College of Engineering