A Two Minute Intro to XML: A Two Minute Intro to XML Roger L. Costello David B. Jacobs The MITRE Corporation (The creation of this tutorial was sponsored by DARPA)


XML is an Acronym: XML is an Acronym … standing for: eXtensible Markup Language


You have data … How should you structure it? : You have data … How should you structure it? medium-altitude, long-endurance unmanned aerial vehicle 14.7 meters 512 kilograms 70 knots Here's some data about an aircraft: 400 nautical miles


The XML approach is to "wrap" each data item in start/end tags: The XML approach is to "wrap" each data item in start/end tags 14.8 meters 512 kilograms 70 knots 400 nautical miles medium-altitude, long-endurance unmanned aerial vehicle RQ-1.xml


XML Terminology: XML Terminology 14.8 meters Start tag End tag Data Element


Why use XML?: Why use XML? It is a universally accepted standard way of structuring data (syntax). It is a W3C recommendation (W3C = World Wide Web Consortium) The marketplace supports it with a lot of free/inexpensive tools. The alternative to using XML is to define your own proprietary data syntax, and then build your own proprietary tools to support the proprietary syntax (Not a very appealing idea).


Why use OWL?: Why use OWL? Roger L. Costello David B. Jacobs The MITRE Corporation (The creation of this tutorial was sponsored by DARPA)


Why use OWL?: Why use OWL? The purpose of this document is to describe the role that OWL plays in data interoperability. [Note: this is not the only use of OWL, but it is an important one.] Contents: Understanding Syntax versus Semantics An example that shows why standardizing syntax is necessary but not sufficient Migrating from defining semantics on a per-application basis to standardized semantics


Syntax versus Semantics: Syntax versus Semantics Syntax: the structure of your data e.g., XML mandates that you structure your data by "wrapping" each data item within a start tag and an end tag pair, with the end tag being preceded by / and both tags in brackets. That is, XML specifies the syntax of your data. Semantics: the meaning of your data Two conditions necessary for interoperability: 1. Adopt a common syntax:this enables applications to parse the data. XML provides a common syntax, and thus is a critical first step. 2. Adopt a means for understanding the semantics: this enables applications to use the data. OWL provides a standard way of expressing the semantics.


What is this XML snippet talking about, i.e., what are the semantics?: What is this XML snippet talking about, i.e., what are the semantics? … What is a Predator?


Predator - which one?: Predator - which one? Predator: a medium-altitude, long-endurance unmanned aerial vehicle system. Predator : one that victimizes, plunders, or destroys, especially for one's own gain. Predator : an organism that lives by preying on other organisms. Predator: a company which specializes in camouflage attire. Predator: a video game. Predator: software for machine networking. Predator: a chain of paintball stores.


Resolving Semantics: Resolving Semantics The next few slides presents an approach that applications can take for understanding the meaning of data. This approach is often taken today. We will then examine the disadvantages of the approach, and then offer a better approach.


Meaning (semantics) applied on a per-application basis: Meaning (semantics) applied on a per-application basis … application Semantics: A Predator is type of Aircraft. Actions: These actions must be performed on the Predator data: - identify ground control station. - determine onboard sensors. - determine ordnance.


Meaning (semantics) applied on a per-application basis: Meaning (semantics) applied on a per-application basis XML app#1 Semantics: Code to interpret the data Action: Code to process the data app#2 Semantics: Code to interpret the data Action: Code to process the data


Problem with attaching semantics on a per-application basis: Problem with attaching semantics on a per-application basis application Semantics: Code to interpret the data Action: Code to process the data Problems with burying semantic definitions within each application: - Duplicate effort - Each application must express the semantics - Variability of interpretation - Each application can take its own interpretation - Example: Mars probe disaster - one application interpreted the data in inches, another application interpreted the data in centimeters. - No ad-hoc discovery and exploitation - Applications have the semantics pre-wired. Thus, when new data (e.g., new type of aircraft) is encountered an application may not be able to effectively process it. This makes for brittle applications. What's a better approach?


Better approach:(1) Extricate semantic definitions from applications (2) Express semantic definitions in a standard vocabulary: Better approach: (1) Extricate semantic definitions from applications (2) Express semantic definitions in a standard vocabulary XML app#1 Action: Code to process the data app#2 Action: Code to process the data OWL Document Semantic Definitions


Recap: Recap Suppose that an application is looking for Aircraft information, and encounters Predator data. Consider the steps the application takes to process the data: (1) Parse the data (this is a syntax issue). (2) Determine the relationship between Predator and Aircraft (this is a semantic issue). Somewhere the following relationship must be made known: (2.1) Predator is a type of Aircraft. Once this information is made known to the application it can then do the following (action) step: (3) If the document contains Aircraft data then do ... Else do ... Issue: Should the semantic definition (2.1) be: (a) hardcoded and buried within each application? or, should it be: (b) declaratively stated in a separate document, using an agreed-upon, well-defined vocabulary (i.e., OWL)? Better approach


OWL provides an agreed-upon vocabulary for expressing semantics: OWL provides an agreed-upon vocabulary for expressing semantics A Sampling of the OWL Vocabulary: subClassOf: this OWL element is used to assert that one class of items is a subset of another class of items. Example: Predator is a subClassOf Aircraft. FunctionalProperty: this OWL element is used to assert that a property has a unique value. Example: sensorID is a FunctionalProperty, i.e., sensorID has a unique value. equivalentClass: this OWL element is used to assert that one Class is equivalent to another Class. Example: Platform is an equivalentClass to Aircraft.


Slide19: OWL Enables Machines to Understand Data! XML/DTD/XML Schemas OWL Syntax Semantics OWL enables machine-processable semantics!


Slide20: Ontology (definition) An Ontology is the collection of semantic definitions for a domain. Example: an Aircraft Ontology is the set of semantic definitions for the Aircraft domain, e.g., Predator is a subClassOf Aircraft. sensorID is a FunctionalProperty. Platform is an equivalentClass to Aircraft.


Why use OWL?: Why use OWL? Benefits to application developers: Less code to write (save $$$). Less chance of misinterpretation (save $$$). Benefits to community at large: Everyone can understand each other's data's semantics, since they are in a common language. OWL uses the XML syntax to express semantics, i.e., it builds on an existing technology. Don't have to learn new syntax. Common XML tools (e.g., parsers) can work on OWL. OWL will soon be a W3C recommendation.


OWL Tutorial: OWL Tutorial Roger L. Costello David B. Jacobs The MITRE Corporation (The creation of this tutorial was sponsored by DARPA)


Location of the Tutorial: Location of the Tutorial http://www.xfront.com/owl/


Layout of the OWL Material: Layout of the OWL Material owl examples example01 example02 labs lab01 lab02 lab03 OWL.ppt Why-use-OWL.ppt OWL-quick-intro.ppt Summary-of-OWL-Capabilities.ppt license.html README.ppt TheRobberAndTheSpeeder.ppt Camera.ppt This Powerpoint document contains the OWL Tutorial. We recommend that you read this document first. A "cheat sheet" that lists (briefly) all of the OWL capabilities. Read this document last. NaturallyOccurringWaterSource Ontology Camera Ontology We recommend that you read this document second. Interesting examples using OWL!


Slide25: Acknowledgment Many thanks to Joe Rockmore for his excellent insight and input into the creation of this document. Thanks Joe!