ssont

Space Surveillance Ontology Captured in an XML Schema: 

Space Surveillance Ontology Captured in an XML Schema Daniel L. Brandsma May 23, 2001 Organization: D540 Project: 03004000

Outline: 

Outline Assumes everyone is aware of what XML is? Ontology task background information Ontology details What is an ontology? The ontology development process Why Space Surveillance? Our ontology approach using XML Schema Space Surveillance ontology contents Conclusions

Ontology Task Background Information: 

Ontology Task Background Information U.S. Air Force responsible for strategic defense C2 systems $1.5 Billion contract awarded in Sept. ‘00 MITRE briefed USAF on need to architect systems that satisfy current C2 requirements, but also scale to meet emerging requirements Capturing domain semantics vital to interoperability Task: Develop preliminary space surveillance ontology Provide insight into applicability of XML in space domain Develop process needed to describe space information objects using XML Use process as pathfinder for cross-community standardization of military space data Investigate and leverage related efforts

What is an ontology?: 

What is an ontology? Ontology = the definitions of the information elements, the individual data items, and the associated inter-relationships For interoperability, understanding data syntax is not enough. Must also understand what the data means.

Ontology Development Process: 

Ontology Development Process Developed preliminary ontology approach Researched relevant XML efforts Selected space surveillance as target domain Selected XML Schema rather than Document Type Definition (DTD) vocabulary Participated in XML training Developed XML ontology approach using only XML Schemas Researched XML tools Developed space surveillance schema Developed ontology demonstration approach Researched registration process of government-wide XML Registry Documented Space Surveillance Ontology

Why Space Surveillance?: 

Why Space Surveillance? Key mission for United States Space Command (USSPACECOM) Prerequisite for all other operations that use space assets A current catalog of where things are in space is a foundation for the military space domain Data content and usage well understood Effort not complicated by trying to define how data to be used Data content, although vital, does not have stringent delivery time requirements XML tags add overhead Didn’t want value of XML based approach obscured by stringent performance requirements Same mission area as related XML demonstration effort

Space Surveillance Ontology Approach: 

Space Surveillance Ontology Approach Decided to use newer XML schema vocabulary over DTDs Document Type Definitions (DTDs) in wide use today but being supplanted by emerging World Wide Web Consortium (W3C) standard called XML Schema XML Schema supports strong data typing, “inheritance”, and cross-namespace linking Invented new approach for developing the space surveillance ontology using only XML Schema Approach could be implemented across broad spectrum of domains

Space Surveillance Ontology XML Schema Approach : 

Space Surveillance Ontology XML Schema Approach

Space Surveillance Ontology Contents: 

Space Surveillance Ontology Contents XML Validator Data Meta-data XSL Processor Data View 1 Definitions Meta- data Data View 2 Data structure Meta-data Definitions .xsd .html .txt .html .html Instance of data content .xml .xml Data Transformations Data Presentations XML Schema PredefinedQuery (e.g., XSQL) Database

Space Surveillance Ontology Contents: 

Space Surveillance Ontology Contents Architecture SpaceSurveillancesData container element holds 5 major elements Each major element in separate file Contains relevant element and attribute declarations Contains relevant type definitions SpaceSurveillanceGlobals file holds type definitions and attribute declarations that apply across all major elements To facilitate reuse To isolate items that may change as schema evolves Metrics 93 elements 39 user defined types 34 attributes (1 attribute group used 16 times) Schema developed in only 2-3 weeks

Space Surveillance Schema Major Element Relationships: 

Space Surveillance Schema Major Element Relationships Satellite Sensor Element Set Tasking Observation Satellite and Elset data are used to generate tasking Elsets and tasking info are sent to sensors Sensors collect observations Observations are used to update Elsets

Ontology DemoSensor Tasking Schema: 

Ontology Demo Sensor Tasking Schema

Ontology DemoSensor Tasking Element Descriptions: 

Ontology Demo Sensor Tasking Element Descriptions

Lessons Learned During Development: 

Lessons Learned During Development An ontology can capture needed data semantics The most difficult part of XML schema development is determining the major information objects XML is not about terseness Our ontology approach is “pushing the technology envelope” XML Schemas are superior to DTDs Schema development is relatively easy with strong domain knowledge available Reuse is powerful and easy to do with XML schemas XML Schema definition language is flexible Incremental integration eased development Use of optional elements can be powerful It is relatively easy to transform XML tagged data

Conclusions: 

Conclusions XML is a technology of choice for interoperability - but it is only one aspect of the total solution Internet standard for data structure and data exchange Enjoys tremendous commercial support (e.g., Sun, MS,…) Provides data transparency Does not define semantics or address data storage Capturing domain semantics is vital to interoperability MITRE analyzed ability of XML to capture semantics and developed results applicable across many domains XML Schema vocabulary preferred approach (over DTDs) Namespaces enable of standard data definitions Expect near-term USAF guidance to C2 programs requiring definition of information objects using XML Schema and registration of tags in XML Registry