The Semantic PDS
J. Steven Hughes
presented by
Elaine Dobinson
PV 2005
The Royal Society, Edinburgh
21-23 November 2005
steve.hughes@jpl.nasa.gov
The Semantic PDS
Topics
• Introduction
• The Planetary Data System (PDS)
• Planetary Science Ontology
• Semantic Web Tools
– Resource Description Framework (RDF)
– Metadata Browsers
• Conclusion
2
The Semantic PDS
Introduction
• The Planetary Data System (PDS) desires more powerful, flexible,
intuitive, and user friendly interfaces to its resources
– The advent of the Web has raised users expections regarding access to
information
– Users now expect “google-like” searches
• Text-based search (e.g. “Titan”)
– But desire “smarter” searches
• Facet-based search (e.g. “Target_Name = Titan”)
• Precision of Forms-based search (e.g. Latitude between 10.0 and -10.0)
• The Semantic Web and the resulting tools and languages are
making this possible
3
The Semantic PDS
Introduction
•
"The Semantic Web is an extension of the current web in
which information is given well-defined meaning, better
enabling computers and people to work in cooperation." -Tim Berners-Lee, James Hendler, Ora Lassila, "The
Semantic Web", Scientific American, May 2001
– Web technologies such as HTML, hyperlinks, and http
protocol have focused on providing information for human
consumption
– New technologies such as Extensible Markup Language
(XML), Resource Description Framework (RDF), and
software agents will provide information sufficient
for computer processing and reasoning
– The semantic web is dependent on the existence of
domain models/ontologies that provide the necessary
semantics
4
The Semantic PDS
Introduction
• In the following we will present a proof-of-concept process for
building a semantic web application
– Describe an existing knowledge-base (PDS Catalog)
• Data model (schema)
• Data (instances)
– Build an ontology from the data model
– Export the knowledge-base to a semantic web language
– Load a shareware metadata browser
– Configure a user interface that allows facet- and text-based searches
• Describe the benefits of using Semantic Web technologies
5
The Semantic PDS
The PDS acquires, preserves, and distributes the large volume of unique
and valuable data returned by Solar System Exploration missions
PDS Overview
NASA’s Planetary Data System
Salient Features (Products & Services)
•
•
•
•
•
•
•
High quality peer-reviewed science data archives
Online data search/retrieval to planetary community
Archiving expertise/standards to planetary missions
Scientific expertise and support for users
Supports mission planning, design, and research
Value-added aggregated data products
Education and outreach data products and services
Science (via Discipline Specialists)
•
•
Engineering Node provides infrastructure system engineering and development, data engineering
and standards, etc. across PDS
Discipline Nodes curates discipline-specific science datasets for use by the science community
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The Semantic PDS
The PDS Data Model
•
The PDS developed the Planetary
Science Data Model in the late 1980’s
•
The PDS data model was
implemented in a relational DBMS and
made operational in 1990.
•
•
–
Catalog of Data Sets
–
Currently ~1000 data sets in catalog
An evolved version of the original data
model remains the key standard for
collecting and organizing archive data
and metadata
–
~50 defined objects (modeled entities)
–
~1,200 data elements (attributes)
–
Maintained in the Planetary Science
Data Dictionary
Data model evolves to reflect
changing domain
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The Semantic PDS
The Planetary Science Ontology
•
The PDS Data Model was
ingested into Stanford’s Protégé
ontology tool
– PDS entities became ontology
classes
• E.g. Data Set, Target, Mission
– PDS data elements became
ontology slots
• E.g. Data_Set_Id,
Data_Set_Desc
• Constraint attributes were
maintained (e.g. Cardinality)
– Included interoperability concepts
from Object-Oriented Data
Technology research
– PDS data records become
ontology instances
• Data records extracted and
ingested
• Produces a knowledge-base
– Export to Resource Description
Framework (RDF)
8
The Semantic PDS
Semantic Web Tools
Resource Description Framework (RDF) (1 of 2)
•
The Resource Description Framework
(RDF) describes resources using
statements in the form of a subjectpredicate-object expression, called a
triple.
1. the resource or "thing" being described
2. the trait or aspect about that resource
(often a relationationship)
3. the object of the relationship or value of
that trait
•
RDF can be represented in an XML
syntax (RDF/XML) that is the standard
representation for access and
exchange of RDF across the Web
<rdf_:Data_set rdf:about="&rdf_;co-s-issna/isswa…“
dc:title="CASSINI ORBITER SATURN ISSNA…"
rdf_:reslocation="http://pdsquery/query?..."
rdf_:resclass="data.metadata.dataset"
dc:publisher="NASA.PDS"
rdf_:data_set_id="CO-S-ISSNA/ISSWA-2-EDR…">
<rdf_:target_name>
<rdf:Description rdf:about="&terms;titan">
<rdfs:label>TITAN</rdfs:label>
</rdf:Description>
</rdf_:target_name>
<rdf_:mission_name>
<rdf:Description rdf:about="&terms;cassini-huygens">
<rdfs:label>CASSINI-HUYGENS</rdfs:label>
</rdf:Description>
</rdf_:mission_name>
</rdf_:Data_set>
RDF/XML for PDS Cassini Imaging Data Set
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The Semantic PDS
Resource Description Framework (RDF) (2 of 2)
•
•
RDF properties may be thought of
as attributes of resources and in this
sense correspond to traditional
attribute-value pairs.
RDF properties also represent
relationships between resources
and an RDF model can therefore
resemble an entity-relationship
diagram.
<rdf_:Data_set rdf:about="&rdf_;co-s-issna/isswa…“
dc:title="CASSINI ORBITER SATURN ISSNA…"
rdf_:reslocation="http://pdsquery/query?..."
rdf_:resclass="data.metadata.dataset"
dc:publisher="NASA.PDS"
rdf_:data_set_id="CO-S-ISSNA/ISSWA-2-EDR…">
<rdf_:target_name>
<rdf:Description rdf:about="&terms;titan">
<rdfs:label>TITAN</rdfs:label>
</rdf:Description>
</rdf_:target_name>
<rdf_:mission_name>
<rdf:Description rdf:about="&terms;cassini-huygens">
<rdfs:label>CASSINI-HUYGENS</rdfs:label>
</rdf:Description>
</rdf_:mission_name>
</rdf_:Data_set>
RDF/XML for PDS Cassini Imaging Data Set
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The Semantic PDS
RDF Schema (RDFS)
•
RDF Schema (RDFS) allows the
definition of sets of terms for a subject
area.
– Resources classes
• Hierarchy of classes
– Resource properties
• Class Properties
– Relationships between classes and
properties
– Characteristics of properties and
classes
•
<rdfs:Class rdf:about="&rdf_;Data_set“
rdfs:label="Data_set">
<rdfs:subClassOf rdf:resource="&rdfs;Resource"/>
</rdfs:Class>
<rdf:Property rdf:about="&rdf_;data_set_id“
rdfs:label="data_set_id">
<rdfs:domain rdf:resource="&rdf_;Data_set"/>
<rdfs:range rdf:resource="&rdfs;Literal"/>
</rdf:Property>
<rdf:Property rdf:about="&rdf_;target_name“
rdfs:label="target_name">
<rdfs:domain rdf:resource="&rdf_;Data_set"/>
<rdfs:domain rdf:resource="&rdf_;Target"/>
<rdfs:range rdf:resource="&rdfs;Literal"/>
</rdf:Property>
RDFS/XML for PDS Data Set
RDFS provides the semantics about
resources, their relationship with other
resources, and their properties and
values.
11
The Semantic PDS
Metadata Browser
•
Longwell
– A suite of web-based RDF browsers
developed by the Simile Project.
– A web application designed to allow browse
and search an RDF model
– Allows browse and search of arbitrarely
complex RDF datasets
•
an end-user friendly view (where all the
complexity of RDF is hidden)
•
an RDF-aware view (where all the details are
shown)
– Written in Java that depends on the following
libraries for operation:
•
•
Apache Velocity as the template engine
•
Apache Lucene as the search engine
•
Jena as the RDF support library (parsing,
storing, querying)
SIMILE (Semantic Interoperability of Metadata and
Information in unLike Environments)
– A joint project conducted by the W3C, MIT
Libraries, and MIT CSAIL.
RDF-aware View
12
The Semantic PDS
Metadata Browser - End-User Friendly View
13
The Semantic PDS
Conclusion
Semantic Web Technology is Now Maturing
• Poweful Ontology (Data Model) Management Tools
– Ontology Capture
• Object classes, attributes, and relationships
• Rich Semantics (Cardinality, inverse relationships, …)
– Ontology Representation
• Standard and novel notations
– UML Class Diagrams
– HTML Documents
– Dynamic drill down GUIs
• New plugins being developed all the time
– Ontology Export
• RDFS/RDF, OWL, Frames, XML Schema/XML, XMI (UML),
Relational Schema
– Implementation Independent
– Promotes Interoperability
• Based on data model semantics
• Commalities between data models are easily exploited
• Inference is supported
14
The Semantic PDS
Semantic Web Technology is Now Maturing
• Ontology + Instances = Knowledge Base
– Ingest and validate domain instances (the data)
– Equally accessible metadata and data
• Browsers for Metadata/Data Navigation
– Generated semi-automatically
– Supports Text-, Facet-, and Forms-Based Search
– Graphical Notations for GUIs being developed
– Allow co-location of differing domain ontologies/knowledge bases
15
The Semantic PDS
Schedule for PDS “Google-Like” Search
•Prototypes – Built and currently evaluating
•White Paper on General Search/Technology Comparison – 12/05
•MC Decision to Proceed – 03/06
•General Data Set Search Deployed – 08/06
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The Semantic PDS
Contacts and URLs
J. Steven Hughes
steve.hughes@jpl.nasa.gov
Daniel Crichton
dan.crichton@jpl.nasa.gov
Semantic PDS Prototype
http://sempds.jpl.nasa.gov/sempds/longwell
SIMILE/Longwell project
http://simile.mit.edu/
PDS
http://pds.jpl.nasa.gov/
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The Semantic PDS
Backup
18
The Semantic PDS
Acronyms and Definitions
DBMS – Data Base Management System
E-R – Entity-Relationship
Facet – A constraint on an attribute
PDS – Planetary Data System
RDF – Resource Descripition Framework
RDFS – RDF Schema
UML – Unified Modeling Language
XMI - XML Metadata Interchange
XML - Extensible Markup Language
Ontology
• Philosophy – Ontology is the study of the existence of things.
• Information Science – An ontology is the product of an attempt
to formulate an exhaustive and rigorous conceptual model about
a specific domain
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The Semantic PDS
Protégé Class Browser
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The Semantic PDS
Protégé HTML Export
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The Semantic PDS
Benefits
Simple
Define
Search
Classify
Planetary
Science
Correlative
Search
Ontology
Data
Describe
Mining
Validate
22