page 1 drexel university, college of engineering achieving semantic interoperability with hydrologic...

Drexel University, College of Engineering

ACHIEVING SEMANTIC INTEROPERABILITY WITH

HYDROLOGIC ONTOLOGIES FOR THE WEB

6th International Conference on

HydroScience and

Engineering

Michael Piasecki Luis Bermudez


• Overview of metadata

• Metadata Interoperability problems

• A possible Solution:

Hydrologic Ontologies for the Web

Content


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

Creator : USGSKeyword: Gage Height

Metadata

Metadata


Hydrologic Information Communities (HIC) need a metadata agreement

What descriptors can be used ?

Keyword or topic

Author or Creator

Gage height or water elevation

Which possible values?

Is there any metadata agreement available to describe hydrologic data ?

Keyword or topic

Author or Creator


Metadata Specifications related to Hydrology

• ISO-19115:2003

• FGDC-STD-001-1998

• Ecological Markup Language

• Geographical Markup Language

• USGS Hydrologic Markup Language

• Earth Science Markup Language

• Dublin Core Metadata Initiative


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 ?


EX_GeographicIdentifier

geographicIdentifier

MD_Identifier

code

…

Descriptive Keywords

MD_Keywords

keyword

Citation …

HIC A creates an HTML form to collect Metadata

#24

Water elev.

X

Not consistent

#23

W #34

#56

=Stage height

HIC A


EX_GeographicIdentifier

geographicIdentifier

MD_Identifier

code

…

Descriptive Keywords

MD_Keywords

keyword

Citation …

Need to incorporate domain vocabulary to get consistent metadata

consistent

consistent

#23 #34 #56

discharge stage height


Problem 2: Metadata standards do not solve Semantic heterogeneities

Finds only data set X

Metadata (FGDC) about dataset Y Theme_Keyword = Gage HeightTheme_Keyword_Thesaurus = USGS

Metadata (ISO) about dataset X keyword = Stage HeightthesaurusName = GCMD

and not data set Y Metadata repository

search for: Stage Height

http://images.google.com/imgres?imgurl=sunnyhill.org/art/clip01/open-door.jpg&imgrefurl=http://sunnyhill.org/go/&h=245&w=209&prev=/images%3Fq%3Dopen%2Bdoor%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8


Possible solutions to our ProblemsHow 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


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.


Ontologies Specification of conceptualizations

Body of Water Class

RiverLake

Has water

Is inland body

Has a defined channel

Lake RiverExample:1. Properties of real

world objects are identified.

2. Similarities are identified.

3. Concepts are created4. and are expressed as

a class. 5. Classes are related.

Subclass


Web Ontology Language : OWL

Body of Water

River Lake

<XML>

</XML>

<owl:Class>Body_of_Water</owl:Class><owl:Class>River</owl:Class><owl:Class>Lake</owl:Class>

W3C Recommendation

since 02/2004


MD_Metadata+ fileIdentifier[0..1] : CharacterString+ language[0..1] : CharacterString…

MD_Identification

…+ abstract : CharacterString…

+ identificationInfo 1..*

Metadata specs expressed in ontologies<XML> Classesdatatype Propertiesobject Properties

<owl:Class>

</owl:Class>

<owl:Class>

</owl:Class>

</XML>

Hydrologic Unit

Region Subregion Accounting Unit

Cataloging Unit

Is part of

Mid Atlantic

Delaware

Lower Delaware

Schuylkill

Is part of

Is part of

Is part of

Class

Subclasses

</XML>

<XML>Is Transitive

Infer isPartOf


More about knowledge Inference

<Station rdf:ID=“A"> </Station><Station rdf:ID=“B"> </Station><Station rdf:ID=“C"> </Station>

<owl:Class rdf:ID “W-Station” type of station that has property isPartOf = W </owl:Class>

<isPartOf rdf:resource=“#W”/>

<isPartOf rdf:resource=“#W”/>

<isPartOf rdf:resource=“#Y”/>

W

A

B

C Y

How to infer the stations that are only in W ?

W-Stations = A, B

Program infer

Dynamic extension with ontologies

Restriction onProperty: code allValuesFrom : W-station

MD_Identifier_Extension+ code: CharacterString…

MD_Identifier+ code: CharacterString…

W-station isPartOf = W

Metadata Specifications Domain Vocabularies

</XML>

<XML> <XML>

</XML>

Program could infer

code AB

Dynamic HTML form using the extension

A

B

C

W

Y

e.g. Restrict the descriptor code to only have W-station values


Ontologies provide means

to resolve Semantic Heterogeneities


Use of ontologies to map metadata specifications

<owl:Class rdf:ID = "&iso;MD_Keywords"><owl:equivalentClass

rdf:resource ="&fgdc;Keywords"/></owl:Class>

<owl:DatatypeProperty rdf:ID = "&iso;title"> <owl:equivalentProperty

rdf:resource = "&fgdc;title“/><owl:DatatypeProperty>


Use of ontologies to solve semantic heterogeneities among different domain

vocabularies

<gcmd:Variable ="&gcmd;Stage_Height">

<owl:sameAs rdf:resource=“&noaa;stage"/>

<owl:sameAs rdf:resource=“&usgs;gage_Height"/>

<owl:differentFrom

rdf:resource=“&events;Stage_Height"/>

</gcmd:Variable>


Semantic Interoperability

Finds data set X and Y

Metadata repository

e.g. search for Stage Height

Metadata (FGDC) about dataset Y Theme_Keyword = Gage HeightTheme_Keyword_Thesaurus = USGS

Metadata (ISO) about dataset X keyword = Stage HeightthesaurusName = GCMD

USGS

GCMD

Mapper

Hydrologic vocabulary

Metadata specifications

FGDC

ISO

Mapper


Why is XML Schema

not good enough?


..<xsd:element ref="watershed" type="watershedType" /><xsd:complexType name="watershedType"> <xsd:sequence> <xsd:element ref="outletLoc“

type="xsd:nonNegativeInteger” minOccurs="1" maxOccurs="1“/> <xsd:element ref=“id" type="xsd:nonNegativeInteger

minOccurs="1" maxOccurs="1"/>

E.g. defining that a watershed has only one outlet location and only one unique identifier

XML Schema cannot express semantics.


XML Schema cannot express semantics

…<watershed> <outletLoc>567</outletLoc> <name>X</name> <id>101</id></watershed>…

…<watershed> <outletLoc>838</outletLoc> <name>X</name> <id>101</id></watershed>…

Valid XML document Valid XML document

Semantically they are not correct 567 <> 838X

XML Schema is good to validate the structure of a document, but not the semantics


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.


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

page 1 drexel university, college of engineering achieving semantic interoperability with hydrologic...

Documents

drexel university

college of engineeringproblem

metadata elements

metadata standards

new metadata specification

college of engineering

metadata agreement available

hydrologic data