THE PURPOSE OF AN ONTOLOGY • To provide a comprehensive description of a certain concept and its relations to other concepts in the same ontology or another ontology WHAT IS AN ONTOLOGY? • Usually an ontology is described as a tree and why should we use it? • But a network is better since more relations can be used cc Per Flensburg 2 1 2 CLASSICAL EXAMPLE BUT WHAT ABOUT THIS? Vehicle Vehicle Land- Water- Land- Water- Airvehicles Airvehicles vehicles vehicles vehicles vehicles Helicopters Airplanes Baloons Helicopters Airplanes Baloons Propeller- Rocket- Jetplanes Passenger- Freight- Sports- Military- planes planes planes planes planes planes Two Four Subsonic- Supersonic- One engine Reconnaissa Bomb- Pursuit- engines engines planes planes nceplanes planes planes cc Per Flensburg 3 cc Per Flensburg 4 3 4 CONFUSING? CLASSICAL EXAMPLE Vehicle Travelling ground • Every level is guided by a principle for distinguish between the Land- Water- Airvehicles objects below. vehicles vehicles • They seem not to be consistent. Lifting principle • This is hidden in a tree diagram, but in a network it can be Helicopters Airplanes Baloons described, since a node in a network has more than one Used for connection. Passenger- Freight- Sports- Military- planes planes planes planes • So let’s see what are the principles in our examples! Used for Reconnaissa Bomb- Pursuit- nceplanes planes planes cc Per Flensburg 5 cc Per Flensburg 6 5 6 BUT WHAT ABOUT THIS? CF A DATA MODEL Vehicle Travelling ground Airplanes Object Land- Water- Airvehicles vehicles vehicles Type of propelling Attribute Lifting principle The Helicopters Airplanes Baloons attributes Number of Attribute Propelling principle are the engines Propeller- Rocket- Jetplanes principles Max planes planes Numbers velocity Attribute of engines Velocity for division! Two Four Subsonic- Supersonic- One engine Used for engines engines planes planes Attribute The principles must be made explicit! cc Per Flensburg 7 cc Per Flensburg 8 7 8 THE DOMAIN OF THE DATA MODEL ONE SUGGESTION Airplanes Civil version Military version Propeller Civil Military But what about airplanes airplanes Type of Rocket Propeller Propeller propelling the military use? Type of Type of Rocket Rocket Jet propelling propelling Number of Jet Jet 1-8 engines Number of Number of 1-8 1-8 engines engines Subsonic Max Subsonic Subsonic velocity Max Max Supersonic velocity velocity Supersonic Supersonic Used for Passenger Used for Used for Passenger Reconaissance Freight Freight Bombing Sport Sport Pursuit Military Note: The data model is the same! cc Per Flensburg 9 cc Per Flensburg 10 9 10 DIFFERENCE BETWEEN THE SIMPLE DATA MODEL TWO VERSIONS • The data model is the same M M Customer Order Parts • The content in the fields belongs to different contexts • Today super-sonic planes are always military planes • We have to describe the contexts in some way! This is in fact a short story saying ”Customers • NOTE: In my communication model I suggest storytelling! order Parts”. A further analysis and normalisation reveals the traditional data model on next slide! • In order to describe the contexts we need more sophisticated description techniques. • Semantic networks is a such group of descriptions cc Per Flensburg 11 cc Per Flensburg 12 11 12 NORMALISED MODEL AIRPLANES I 1 M M Civil Airplane has type Customer place Order airplanes 1 I has Military M has type M airplanes Part is on Orderline 1 M One airplane has type many civil airplanes. One customer places many orders. One order has One airplane has type many military airplanes many orderlines. One part is on many orderlines. The story should say something about the domain This makes no sense! we are modelling. It should be correct! cc Per Flensburg 13 cc Per Flensburg 14 13 14 IT DOES NOT MAKE SENSE BECAUSE OF • One plane can only be of one type! • In the model ”Airplane” is a superior class of ”civil airplane” HOW TO CREATE AN and ”military airplane” and this can not be modelled in a database. Or...? ONTOLOGY • The sets of attributes to civil and military airplanes are partly Based upon: Ontology Development 101: A Guide to Creating overlapping (inheritance!) Your First Ontology • So how do you tell a story about this? cc Per Flensburg 15 15 16 ORIGIN OF THE ONTOLOGY AI AND ONTOLOGIES CONCEPT 1. From philosophy Will be discussed later • Explicit formal specifications of the terms in the domain and 2. From data base theory Was discusssed earlier relations among them (Gruber 1993) 3. From artificial intelligence • Synonyms: Taxonomy, thesaurus, word list 4. From systems integration Will be discussed later • Purpose: Make people understand what is written in the database or on the web page • The WWW Consortium (W3C) is developing the Resource Description Framework (Brickley and Guha 1999), a language for encoding knowledge on Web pages to make it understandable to electronic agents searching for information. cc Per Flensburg 17 cc Per Flensburg 18 17 18 WHY DEVELOP AN FORMAL DEFINITION IN THIS ONTOLOGY? GUIDE • To share common understanding of the structure of • An ontology is a formal explicit description of concepts in a information among people or software agents domain of discourse (classes (sometimes called concepts)), • To enable reuse of domain knowledge properties of each concept describing various features and attributes of the concept (slots (sometimes called roles or • To make domain assumptions explicit properties)), and restrictions on slots (facets • To separate domain knowledge from the operational (sometimes called role restrictions)). knowledge (control and meta information) • An ontology together with a set of individual instances of • To analyse domain knowledge classes constitutes a knowledge base. In reality, there is a fine line where the ontology ends and the knowledge base begins. cc Per Flensburg 19 cc Per Flensburg 20 19 20 TO DEVELOP AN ONTOLOGY EXAMPLE • define classes in the ontology, • A class of wines represents all wines. Specific wines are • arrange the classes in a taxonomic (subclass–superclass) instances of this class. The Bordeaux wine I drank last week- hierarchy, end is an instance of the class of Bordeaux wines. • define slots and describing allowed values for these slots, • A class can have subclasses that represent concepts that are more specific than the superclass. For example, we can divide • fill in the values for slots for instances. the class of all wines into red, white, and rosé wines. • Alternatively, we can divide a class of all wines into sparkling This was exactly what we did in the airplane example! and non-sparkling wines • Here I will use French wines as example. cc Per Flensburg 21 cc Per Flensburg 22 21 22 FRANCE DATA MODEL M 1 Wine is made by Winery M M is of 1 1 Type Produces Many wines is made by one winery. Many wineries produces one type. Many wines is of one type cc Per Flensburg 23 cc Per Flensburg 24 23 24 INSTANCE BUT WHAT ABOUT Chateux Lafite Chateux Lafite Rotschild Rotschild Rotschild is made by Rotschild is made by is of is of Bordeaux Produces Pauillac Produces cc Per Flensburg 25 cc Per Flensburg 26 25 26 RESOLUTION AND YET MORE Chateux Lafite is made by Rotschild Chateux Lafite Rotschild Rotschild Rotschild is made by is of is of Pauillac grand vin Produces Pauillac Produces is of is of Mouton- Bordeaux Latour Bordeaux Rotschild cc Per Flensburg 27 cc Per Flensburg 28 27 28 BORDEAUX MEDOC WINES WINE DISTRICTS cc Per Flensburg 29 cc Per Flensburg 30 29 30 WINE ONTOLOGY NOTE: • There is no one correct way to model a domain • Ontology development is necessarily an iterative process. • Concepts in the ontology should be close to objects (physical or logical) and relationships in your domain of interest. These are most likely to be nouns (objects) or verbs (relationships) in sentences that describe your domain. Some classes, instances, and relations among them in the wine domain. We used black for classes and red for instances. Direct links represent slots and internal links such as instance-of and subclass-of. cc Per Flensburg 31 cc Per Flensburg 32 31 32 STEPS DOMAIN AND SCOPE • Step 1. Determine the domain and scope of the ontology •What is the domain that the ontology will cover? • Step 2. Consider reusing existing ontologies •For what we are going to use the ontology? • Step 3. Enumerate important terms in the ontology •For what types of questions the information in the ontology • Step 4. Define the classes and the class hierarchy should provide answers? • Step 5. Define the properties of classes—slots •Who will use and maintain the ontology? • Step 6. Define the facets of the slots • Step 7. Create instances cc Per Flensburg 33 cc Per Flensburg 34 33 34 EXAMPLE COMPETENCY QUESTIONS • Which wine characteristics should I consider when choosing a • Domain: Representation of food and wines wine? • Application: Suggest good combinations of wines and food • Is Bordeaux a red or white wine? • If the ontology will be used to assist in natural language • Does Cabernet Sauvignon go well with seafood? processing of articles in wine magazines, it may be important to include synonyms • What is the best choice of wine for grilled meat? • If the ontology will be used to help restaurant customers • Which characteristics of a wine affect its appropriateness for decide which wine to order, we need to include retail-pricing a dish? information • Does a bouquet or body of a specific wine change with • If it is used for wine buyers in stocking a wine cellar, wholesale vintage year? pricing and availability may be necessary. • What were good vintages for Napa Zinfandel? cc Per Flensburg 35 cc Per Flensburg 36 35 36 REUSING EXISTING WINE ONTOLOGIES ONTOLOGIES • Many ontologies are available in electronic form and can be • http://www.daml.org/ontologies/76 imported into an ontology-development environment • Gives names of classes and of properties • The formalism in which an ontology is expressed often does • http://www.dmoz.org/Home/Cooking/Beverages/Wine/ not matter, since many knowledge-representation systems can • import and export ontologies.