Software Agents and Multiagent Systems Ontologies

Transcription

1 Software Agents and Multiagent Systems Ontologies Viviana Mascardi SIIT Master, University of Genoa (DISI) SIIT Master, University of Genoa Software Agents and MASs 1 / 84

2 Disclaimer This presentation may contain material protected by copyright laws. In particular, many lessons are based on the material that Russel and Norvig made available on the Web, as part of their book Artificial Intelligence: A Modern Approach We made this material available on the Web only to ensure timely dissemination among the students of the SIIT Master, and is meant only for students personal use. Any use different from the students personal use is prohibited. SIIT Master, University of Genoa Software Agents and MASs 2 / 84

3 1 Introduction to ontologies Definition 2 Ontology Development Foundamental Steps 3 Development tools Protégé SIIT Master, University of Genoa Software Agents and MASs 3 / 84

4 Figure: This is Aristotle! SIIT Master, University of Genoa Software Agents and MASs 4 / 84 Introduction to ontologies Definition What is an ontology? - Aristotle s definition The term ontology comes from the field of philosophy that is concerned with the study of being or existence. In philosophy, one can talk about an ontology as a theory of the nature of existence (e.g., Aristotle s ontology offers primitive categories, such as substance and quality, which were presumed to account for All That Is).

5 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 1993 Explicit specification of a conceptualization Tom Gruber, A Translation Approach to Portable Ontology Specifications, Knowledge Acquisition, 5(2): , Figure: This is Tom Gruber! SIIT Master, University of Genoa Software Agents and MASs 5 / 84

6 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 In the context of computer and information sciences, an ontology defines a set of representational primitives with which to model a domain of knowledge or discourse. SIIT Master, University of Genoa Software Agents and MASs 6 / 84

7 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 In the context of computer and information sciences, an ontology defines a set of representational primitives with which to model a domain of knowledge or discourse. The representational primitives are typically classes (or sets), attributes (or properties), and relationships (or relations among class members). SIIT Master, University of Genoa Software Agents and MASs 6 / 84

8 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 In the context of computer and information sciences, an ontology defines a set of representational primitives with which to model a domain of knowledge or discourse. The representational primitives are typically classes (or sets), attributes (or properties), and relationships (or relations among class members). The definitions of the representational primitives include information about their meaning and constraints on their logically consistent application. SIIT Master, University of Genoa Software Agents and MASs 6 / 84

9 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 In the context of database systems, ontology can be viewed as a level of abstraction of data models, analogous to hierarchical and relational models, but intended for modeling knowledge about individuals, their attributes, and their relationships to other individuals. SIIT Master, University of Genoa Software Agents and MASs 7 / 84

10 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 In the context of database systems, ontology can be viewed as a level of abstraction of data models, analogous to hierarchical and relational models, but intended for modeling knowledge about individuals, their attributes, and their relationships to other individuals. Ontologies are typically specified in languages that allow abstraction away from data structures and implementation strategies; in practice, the languages of ontologies are closer in expressive power to first-order logic than languages used to model databases. SIIT Master, University of Genoa Software Agents and MASs 7 / 84

11 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 In the context of database systems, ontology can be viewed as a level of abstraction of data models, analogous to hierarchical and relational models, but intended for modeling knowledge about individuals, their attributes, and their relationships to other individuals. Ontologies are typically specified in languages that allow abstraction away from data structures and implementation strategies; in practice, the languages of ontologies are closer in expressive power to first-order logic than languages used to model databases. For this reason, ontologies are said to be at the semantic level, whereas database schema are models of data at the logical or physical level. SIIT Master, University of Genoa Software Agents and MASs 7 / 84

12 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 Due to their independence from lower level data models, ontologies are used for integrating heterogeneous databases, enabling interoperability among disparate systems, and specifying interfaces to independent, knowledge-based services. SIIT Master, University of Genoa Software Agents and MASs 8 / 84

13 Introduction to ontologies Definition What is an ontology? - Tom Gruber s Definition, 2008 Due to their independence from lower level data models, ontologies are used for integrating heterogeneous databases, enabling interoperability among disparate systems, and specifying interfaces to independent, knowledge-based services. In the technology stack of the Semantic Web standards, ontologies are called out as an explicit layer. There are now standard languages and a variety of commercial and open source tools for creating and working with ontologies. Tom Gruber, Ontology, to appear in the Encyclopedia of Database Systems, Ling Liu and M. Tamer Özsu (Eds.), Springer-Verlag, SIIT Master, University of Genoa Software Agents and MASs 8 / 84

14 An Example Introduction to ontologies Definition Figure: Wine Ontology SIIT Master, University of Genoa Software Agents and MASs 9 / 84

15 Introduction to ontologies Ontologies and Databases Definition Figure: Ontologies and Databases SIIT Master, University of Genoa Software Agents and MASs 10 / 84

16 Introduction to ontologies Definition Ontologies and Databases Purpose Ontologies: Sharing, reuse, defining semantics. Databases: storing large amounts of structured data. Expressive power of modelling languages Ontologies: close first order logic; description logics. Databases: not as powerful as FOL. SIIT Master, University of Genoa Software Agents and MASs 11 / 84

17 Introduction to ontologies Definition Ontologies and Databases Standards for making queries Ontologies: no standards, few proposals, for example SPARQL. Databases: consolidated standards, for example SQL. Management systems Ontologies: Protégé, Jena (not commercial). Databases: Many solid, commercial tools and environments (Oracle, etc). SIIT Master, University of Genoa Software Agents and MASs 12 / 84

18 Ontology Development Foundamental Steps Methodology for ontology development Natalya F. Noy and Deborah L. McGuinness, Ontology Development 101: A Guide to Creating Your First Ontology, Knowledge Systems Laboratory, March, development/ontology101-noy-mcguinness.html SIIT Master, University of Genoa Software Agents and MASs 13 / 84

19 Ontology Development Foundamental Steps Methodology for ontology development Natalya F. Noy and Deborah L. McGuinness, Ontology Development 101: A Guide to Creating Your First Ontology, Knowledge Systems Laboratory, March, development/ontology101-noy-mcguinness.html Determine the domain and scope of the ontology Consider reusing existing ontologies Enumerate important terms in the ontology Define the classes and the class hierarchy Define the properties of classes-slots Define the facets of the slots Create instances SIIT Master, University of Genoa Software Agents and MASs 13 / 84

20 Ontology Development Foundamental Steps 1. Determine the domain and scope of the ontology Answer several basic questions: What is the domain that the ontology will cover? For what we are going to use the ontology? For what types of questions the information in the ontology should provide answers? Who will use and maintain the ontology? One of the ways to determine the scope of the ontology is to sketch a list of competency questions, namely, questions that a knowledge base, based on the ontology, should be able to answer. SIIT Master, University of Genoa Software Agents and MASs 14 / 84

21 Ontology Development Foundamental Steps 1. Determine the domain and scope of the ontology Once defined, the consistency of the ontology, w.r.t the initial requirements, can be verified by asking: SIIT Master, University of Genoa Software Agents and MASs 15 / 84

22 Ontology Development Foundamental Steps 1. Determine the domain and scope of the ontology Once defined, the consistency of the ontology, w.r.t the initial requirements, can be verified by asking: Does the ontology contain enough information to answer these types of questions? SIIT Master, University of Genoa Software Agents and MASs 15 / 84

23 Ontology Development Foundamental Steps 1. Determine the domain and scope of the ontology Once defined, the consistency of the ontology, w.r.t the initial requirements, can be verified by asking: Does the ontology contain enough information to answer these types of questions? Do the answers require a particular level of detail or representation of a particular area? These competency questions are just a sketch and do not need to be exhaustive SIIT Master, University of Genoa Software Agents and MASs 15 / 84

24 Ontology Development Foundamental Steps Domain and scope of the ontology - Example Let s consider a ontology describing different types of wines, main food types, the notion of a good combination of wine and food, a bad combination etc. Let s see some of the possible competency questions: SIIT Master, University of Genoa Software Agents and MASs 16 / 84

25 Ontology Development Foundamental Steps Domain and scope of the ontology - Example Let s consider a ontology describing different types of wines, main food types, the notion of a good combination of wine and food, a bad combination etc. Let s see some of the possible competency questions: Which wine characteristics should I consider when choosing a wine? Is Bordeaux a red or white wine? Is Cabernet Sauvignon suitable for accompanying seafood? What is the best choice of wine for grilled meat? Does a bouquet or body of a specific wine change with vintage year? What were good vintages for Napa Zinfandel? SIIT Master, University of Genoa Software Agents and MASs 16 / 84

26 Ontology Development Foundamental Steps 2. Consider reusing existing ontologies Reusing existing ontologies may be a requirement if our system needs to interact with other applications that have already committed to particular ontologies or controlled vocabularies. Many ontologies are already available in electronic form and can be imported into an ontology-development environment that you are using. There are libraries of reusable ontologies on the Web and in the literature. For example, we can use the Ontolingua ontology library ( or the DAML ontology library ( SIIT Master, University of Genoa Software Agents and MASs 17 / 84

27 Ontology Development Foundamental Steps 3. Enumerate important terms in the ontology Write down a list of all terms you would like either to make statements about or to explain to a user. What are the terms you would like to talk about? What properties do those terms have? What would you like to say about those terms? SIIT Master, University of Genoa Software Agents and MASs 18 / 84

28 Ontology Development Foundamental Steps 3. Enumerate important terms in the ontology Write down a list of all terms you would like either to make statements about or to explain to a user. What are the terms you would like to talk about? What properties do those terms have? What would you like to say about those terms? For example, important wine-related terms will include wine, grape, winery, location, a wine s color, body, flavor and sugar content; different types of food, such as fish and red meat; subtypes of wine such as white wine, and so on. Initially, it is important to get a comprehensive list of terms without worrying about overlaps between concepts they represent, relations among the terms, or any properties that the concepts may have, or whether the concepts are classes or slots. SIIT Master, University of Genoa Software Agents and MASs 18 / 84

29 Ontology Development Foundamental Steps 4. Define the classes and the class hierarchy Top-down: definition of the most general concepts in the domain and subsequent specialization of the concepts. Bottom-up: definition of the most specific classes, the leaves of the hierarchy, with subsequent grouping of these classes into more general concepts. Middle Out: We define the more salient concepts first and then generalize and specialize them appropriately. From the list created in the previous step, we select the terms that describe objects having independent existence rather than terms that describe these objects and then we organize the classes into a hierarchical taxonomy. If a class A is a superclass of class B, then every instance of B is also an instance of A SIIT Master, University of Genoa Software Agents and MASs 19 / 84

30 Ontology Development 4. Define the class hierarchy Foundamental Steps Figure: Class Hierarchy SIIT Master, University of Genoa Software Agents and MASs 20 / 84

31 Ontology Development Foundamental Steps 5. Define the properties of classes slots Once we have defined some of the classes, we must describe the internal structure of concepts. In general, there are several types of object properties that can become slots in an ontology: intrinsic properties such as the flavor of a wine; extrinsic properties such as a wine s name, and area it comes from; parts, if the object is structured; these can be both physical and abstract parts (e.g., the courses of a meal); relationships to other individuals; these are the relationships between individual members of the class and other items (e.g., the maker of a wine, representing a relationship between a wine and a winery, and the grape the wine is made from.) SIIT Master, University of Genoa Software Agents and MASs 21 / 84

32 Ontology Development Foundamental Steps 5. Define the properties of classes slots Figure: Properties of the class Wine SIIT Master, University of Genoa Software Agents and MASs 22 / 84

33 Ontology Development Foundamental Steps 6. Define the facets of the slots For each slot we define facets describing the features of the value that it can take. Cardinality. How many values a slot can have. Value type. What types of values can fill in the slot: String Number Boolean Enumerated Istance-type Domain and range. Allowed classes for slots of type Instance are often called a range of a slot. The classes to which a slot is attached or a classes which property a slot describes, are called the domain of the slot. SIIT Master, University of Genoa Software Agents and MASs 23 / 84

34 Ontology Development 6. Define the facets of the slots Foundamental Steps Figure: Facets of the property maker SIIT Master, University of Genoa Software Agents and MASs 24 / 84

35 7. Create Instance Ontology Development Foundamental Steps Choose a class, Create an individual instance of class, and Fill its slot values. Figure: Instance of a class SIIT Master, University of Genoa Software Agents and MASs 25 / 84

36 Development tools Protégé Protégé Protégé is a free, open source ontology editor and knowledge-base framework. Developed by the Stanford University, Protégé is based on Java, is extensible, and provides a plug-and-play environment that makes it a flexible base for rapid prototyping and application development. The Protégé platform supports two main ways of modeling ontologies: The Protégé-Frames editor enables users to build and populate ontologies that are frame-based. The Protégé-OWL editor enables users to build ontologies for the Semantic Web, in particular in the W3C s. For more details: SIIT Master, University of Genoa Software Agents and MASs 26 / 84

37 4 Semantic Web 5 Ontology Languages for the Semantic Web RDF DAML+OIL OWL 6 Ontology and JADE 7 WordNet Definition The WordNet ontology SIIT Master, University of Genoa Software Agents and MASs 27 / 84

38 Semantic Web What is the Semantic Web? The Semantic Web is not a separate Web but an extension of the current one, in which information is given a well-defined meaning, better enabling computers and people to work in cooperation. Tim Berners-Lee, James Hendler and Ora Lassila; Scientific American, May 2001 Automatic discovery of web resources and web services Automatic composition of web resources and web services Automatic execution and monitoring of web services SIIT Master, University of Genoa Software Agents and MASs 28 / 84

39 Semantic Web What we expect from the Semantic Web? The Semantic Web aims to provide a common framework that allows data to be shared and reused across application. Ontologies plays therefore a crucial role in the development of the Semantic Web because they are suitable to process and to share knowledge. SIIT Master, University of Genoa Software Agents and MASs 29 / 84

40 Semantic Web What we expect from the Semantic Web? The Semantic Web aims to provide a common framework that allows data to be shared and reused across application. Ontologies plays therefore a crucial role in the development of the Semantic Web because they are suitable to process and to share knowledge. To add semantics to the contents of the Web, a language that allows to express data and rules for reasoning is needed. SIIT Master, University of Genoa Software Agents and MASs 29 / 84

41 Ontology Languages for the Semantic Web Languages Evolution Figure: Languages Evolution SIIT Master, University of Genoa Software Agents and MASs 30 / 84

42 Ontology Languages for the Semantic Web RDF - RDF Model and Syntax & RDF Schema RDF RDF is a W3C recommendation and provides a general, flexible method to decompose any knowledge into small pieces, called triples, with some rules about the semantics (meaning) of those pieces. The RDF data model provides three object types: A resource may be either entire Web page, a part of it, a whole collections of pages, or an object that is not directly accessible via the Web; A property is a specific aspect, characteristics, attribute, or relation used to describe a resource. A statement is a triple consisting of two nodes and a connecting edge. These basic elements are all kinds of RDF resources SIIT Master, University of Genoa Software Agents and MASs 31 / 84

43 Ontology Languages for the Semantic Web RDF Statement RDF Basic Idea: triple (O, A, V ) more frequently written as A(O, V ). Meaning: an object O has an attributes A with value V. Figure: An RDF Graph SIIT Master, University of Genoa Software Agents and MASs 32 / 84

44 Example Ontology Languages for the Semantic Web RDF <?xml v e r s i o n = 1.0?> <r d f : RDF xmlns : r d f = h t t p : / /www. w3. org /1999/02/22 r d f syntax ns# xmlns : a= h t t p : / / domain name / author schema/ > <r d f : D e s c r i p t i o n about= h t t p : / / domain name / example. html > <a : author > Mario R o s s i </a : author > </ r d f : D e s c r i p t i o n > </ r d f : RDF> The description is represented by the tag rdf:description and its attribute about identifies the resource to which it refers. The property of the statements is described using the tag a:author. SIIT Master, University of Genoa Software Agents and MASs 33 / 84

45 RDF Schema Ontology Languages for the Semantic Web RDF RDF schemas are used to define the structure of the metadata that are used to describe WWW resources (i.e. WWW pages or parts of WWW pages, referenced by an URL). The RDF Schema Specification consists of some basic classes and properties, and can be extended by others to fit possibly any given domain. Classes are arranged hierarchically, and the use of properties can be constrained to members of certain classes. The root of the class hierarchy is rdfs:resource, rdfs:class is subclass of rdfs:resource. Properties are defined by the rdf:property class and can be seen as attributes, that are used to describe resources by assigning values to them. Properties are resources themselves. SIIT Master, University of Genoa Software Agents and MASs 34 / 84

46 Example RDFS Ontology Languages for the Semantic Web RDF <r d f s : C l a s s r d f : ID= Teacher > <r d f s : comment>teacher C l a s s </r d f s : comment> <r d f s : s u b C l a s s O f r d f : r e s o u r c e= #Person /> </ r d f s : C l a s s> <r d f s : C l a s s r d f : ID= Course > <r d f s : comment>course C l a s s </r d f s : comment> <r d f s : subclassof r d f : resource= http : / /www. w3. org /1999/02/22 rdf syntax ns#resource /> </ r d f s : C l a s s> <r d f : P r o p e r t y r d f : ID= t e a c h e r > <r d f s : comment>teacher o f a c o u r s e </r d f s : comment> <r d f s : domain r d f : r e s o u r c e= #Course /> <r d f s : r a n g e r d f : r e s o u r c e= #Teacher /> </r d f : P r o p e r t y> <r d f : P r o p e r t y r d f : ID= name > <r d f s : comment>name o f a Person o r Course </r d f s : comment> <r d f s : domain r d f : r e s o u r c e= #Person /> <r d f s : domain r d f : r e s o u r c e= #Course /> <r d f s : r a n g e r d f : r e s o u r c e = h t t p : / /www. w3. org /1999/02/22 r d f s yntax ns#l i t e r a l /> </r d f : P r o p e r t y> SIIT Master, University of Genoa Software Agents and MASs 35 / 84

47 DAML+OIL Ontology Languages for the Semantic Web DAML+OIL DAML+OIL is the result of a merger between DAML-ONT, a language developed as part of the US DARPA Agent Markup Language (DAML) and OIL (the Ontology Inference Layer), developed by a group of (mostly) European researchers. DAML+OIL is designed to describe the structure of a domain; it takes an object oriented approach, describing the structure in terms of classes and properties. An ontology consists of a set of axioms that assert, e.g., subsumption relationships between classes or properties. SIIT Master, University of Genoa Software Agents and MASs 36 / 84

48 Ontology Languages for the Semantic Web DatatypeProperty DAML+OIL DAML+OIL allows property values to be restricted to the data types defined in XSDL or to user-defined data types. Define a new property: DatatypeProperty <r d f s : P r o p e r t y r d f : ID= productnumber > <r d f s : l a b e l >Product Number</ r d f s : l a b e l > <r d f s : domain r d f : r e s o u r c e= #Product /> <r d f s : range r d f : r e s o u r c e= h t t p : / /www. w3. org /2000/01/ r d f schema#l i t e r a l /> </ r d f s : Property > SIIT Master, University of Genoa Software Agents and MASs 37 / 84

49 Ontology Languages for the Semantic Web DatatypeProperty DAML+OIL DAML+OIL allows property values to be restricted to the data types defined in XSDL or to user-defined data types. Define a new property: DatatypeProperty <daml : D a t a t y p e P r o p e r t y r d f : ID= productnumber > <r d f s : l a b e l >Product Number</ r d f s : l a b e l > <r d f s : domain r d f : r e s o u r c e= #Product /> <r d f s : range r d f : r e s o u r c e= h t t p : / /www. w3. org /2000/10/XMLSchema#n o n N e g a t i v e I n t e g e r /> </daml : DatatypeProperty > SIIT Master, University of Genoa Software Agents and MASs 38 / 84

50 Ontology Languages for the Semantic Web DatatypeProperty DAML+OIL DAML+OIL allows property values to be restricted to the data types defined in XSDL or to user-defined data types. You can also specify that a property be unique <daml : D a t a t y p e P r o p e r t y r d f : ID= productnumber > <r d f s : l a b e l >Product Number</ r d f s : l a b e l > <r d f s : domain r d f : r e s o u r c e= #Product /> <r d f s : range r d f : r e s o u r c e= h t t p : / /www. w3. org /2000/10/XMLSchema#n o n N e g a t i v e I n t e g e r /> <r d f : t y p e r d f : r e s o u r c e= h t t p : / /www. w3. org /2001/10/ daml+o i l#u n i q u e P r o p e r t y /> </daml : DatatypeProperty > SIIT Master, University of Genoa Software Agents and MASs 39 / 84

51 DAML+OIL Ontology Languages for the Semantic Web DAML+OIL daml:class The class daml:class is deifned as a subclass of the class rdf:class, and it adds some new features. For example a new features is about the enumeration. <r d f s : C l a s s r d f : ID= M a r i t a l S t a t u s /> <M a r i t a l S t a t u s r d f : ID= Married /> <M a r i t a l S t a t u s r d f : ID= D i v o r c e d /> <M a r i t a l S t a t u s r d f : ID= S i n g l e /> <M a r i t a l S t a t u s r d f : ID= Widowed /> The problem of RDF is that we can add items to the enumerations without restrictions. DAML+OIL proposes to structure the enumerations. SIIT Master, University of Genoa Software Agents and MASs 40 / 84

52 DAML+OIL Ontology Languages for the Semantic Web DAML+OIL <daml : C l a s s ID= M a r i t a l S t a t u s > <daml : oneof parsetype= daml : c o l l e c t i o n > <daml : Thing r d f : ID= Married > <r d f s : l a b e l >Married </ r d f s : l a b e l > </daml : Thing> <daml : Thing r d f : ID= D i v o r c e d > <r d f s : l a b e l >Divorcedd </ r d f s : l a b e l > </daml : Thing> <daml : Thing r d f : ID= S i n g l e > <r d f s : l a b e l >S i n g l e </ r d f s : l a b e l > </daml : Thing> <daml : Thing r d f : ID= Widowed > <r d f s : l a b e l >Widowed</ r d f s : l a b e l > </daml : Thing> </daml : oneof> </daml : C l a s s > The element daml:oneof defines an enumeration using the constructor (daml:collection) that allows to define closed lists. SIIT Master, University of Genoa Software Agents and MASs 41 / 84

53 Ontology Languages for the Semantic Web OWL OWL (Ontology Web Language) OWL is an extension of RDF Schema, in the sense that OWL would use the RDF meaning of classes and properties ( rdfs:class, rdfs:subclassof, etc), and would add language primitives to support a richer expressiveness. OWL Full: It uses all the OWL languages primitives. It also allows to combine these primitives in arbitrary ways with RDF and RDF Schema. The advantage of OWL Full is that it is fully upward compatible with RDF. The disadvantage of OWL Full is that the language has become so powerful as to be undecidable. SIIT Master, University of Genoa Software Agents and MASs 42 / 84

54 Ontology Languages for the Semantic Web OWL OWL (Ontology Web Language OWL DL: It is a sublanguage of OWL Full which restricts the way in which the constructors from OWL and RDF can be used. The advantage of this is that it permits efficient reasoning support. The disadvantage is that we loose full compatibility with RDF. OWL Lite: An ever further restriction limits OWL DL to a subset of the language constructors. The advantage of this is a language that is both easier to grasp (for users) and easier to implement (for tool builders). The disadvantage is of course a restricted expressivity. SIIT Master, University of Genoa Software Agents and MASs 43 / 84

55 OWL Syntax Ontology Languages for the Semantic Web OWL <r d f : RDF xmlns : owl = h t t p : / /www. w3. org /2002/07/ owl# xmlns : r d f = h t t p : / /www. w3. org /1999/02/22 r d f syntax ns# xmlns : r d f s = h t t p : / /www. w3. org /2000/01/ r d f schema# xmlns : xsd = h t t p : / /www. w3. org /2001/XLMSchema# > <owl : Ontology r d f : about= > <r d f s : comment>an example OWL o n t o l o g y </ r d f s : comment> <owl : p r i o r V e r s i o n r d f : r e s o u r c e = h t t p : / /www. mydomain. org / uni ns o l d /> <owl : i m p o r t s r d f : r e s o u r c e = h t t p : / /www. mydomain. org / p e r s o n s /> <r d f s : l a b e l >U n i v e r s i t y Ontology </ r d f s : l a b e l > </owl : Ontology> owl:imports it includes other ontologies whose content is assumed to be part of the current document. Also note that owl:imports is a transitive property: if ontology A imports ontology B, and ontology B imports ontology C, then ontology A also imports ontology C. SIIT Master, University of Genoa Software Agents and MASs 44 / 84

56 Classes in OWL Ontology Languages for the Semantic Web OWL Classes are defined using the element owl:class <owl : C l a s s r d f : ID= Male > <r d f s : s u b C l a s s O f r d f : r e s o u r c e= #Person /> </owl : C l ass > SIIT Master, University of Genoa Software Agents and MASs 45 / 84

57 Classes in OWL Ontology Languages for the Semantic Web OWL Classes are defined using the element owl:class <owl : C l a s s r d f : ID= Male > <r d f s : s u b C l a s s O f r d f : r e s o u r c e= #Person /> </owl : C l ass > For example We can add the information that this class is disjoint with the class Femmine through the element owl:disjointwith. SIIT Master, University of Genoa Software Agents and MASs 45 / 84

58 Classes in OWL Ontology Languages for the Semantic Web OWL Classes are defined using the element owl:class <owl : C l a s s r d f : ID= Male > <r d f s : s u b C l a s s O f r d f : r e s o u r c e= #Person /> </owl : C l ass > For example We can add the information that this class is disjoint with the class Femmine through the element owl:disjointwith. <owl : C l a s s r d f : about= Male > <owl : d i s j o i n t W i t h r d f : r e s o u r c e= #Female /> </owl : C l ass > There are two predefined classes: owl:thing and owl:nothing. SIIT Master, University of Genoa Software Agents and MASs 45 / 84

59 Property in OWL Ontology Languages for the Semantic Web OWL Two types of property: Object properties link individuals to individuals. Datatype properties link individuals to data values. <owl : D a t a t y p e P r o p e r t y r d f : ID= age > <r d f s : range r d f : r e s o u r c e = h t t p : / /www. w3. org /2001/XMLSchema #n o n N e g a t i v e I n t e g e r /> <owl : domain r d f : r e s o u r c e= #Person /> </owl : DatatypeProperty > <owl : O b j e c t P r o p e r t y r d f : ID= m a r r i e d > <owl : domain r d f : r e s o u r c e= #Person /> <owl : range r d f : r e s o u r c e= #Person /> </owl : O b j e c t P r o p e r t y > SIIT Master, University of Genoa Software Agents and MASs 46 / 84

60 Credits Ontology Languages for the Semantic Web OWL RDF RDFS DAML+OIL OWL SIIT Master, University of Genoa Software Agents and MASs 47 / 84

61 Ontology and JADE Why Ontology in JADE? Inside the ACL message, I is represented as a content expression consistent with a proper content language (e.g. SL) and encoded in a proper format (e.g. string). For example the information: there is a person whose name is Giovanni and who is 33 years old could be represented as (Person :name Giovanni :age 33) Both A and B have their own (possibly different) way of internally representing I. SIIT Master, University of Genoa Software Agents and MASs 48 / 84

62 Ontology and JADE Why Ontology in JADE? For example representing the above information about Giovanni as an instance (a Java object) of an application-specific class class Person { String name; int age; } public String getname() {return name; } public void setname(string n) {name = n; } public int getage() {return age; } public void setage(int a) {age = a; }... initialized with name = Giovanni ; age = 33; would allow to handle it very easily. SIIT Master, University of Genoa Software Agents and MASs 49 / 84

63 Ontology and JADE Why Ontology in JADE? 1 A needs to convert his internal representation of I into the corresponding ACL content expression representation and B needs to perform the opposite conversion. 2 Moreover B should also performs a number of semantic checks to verify that I is a meaningful piece of information, i.e. that it complies with the rules (for instance that the age of Giovanni is actually an integer value) of the ontology by means of which both A and B ascribe a proper meaning to I. SIIT Master, University of Genoa Software Agents and MASs 50 / 84

64 Ontology in JADE Ontology and JADE JADE provides extensive support for ontologies. The agents communicate using standard FIPA ontolgies. JADE provides support for user defined ontolgies as well. JADE support for user ontolgies is in the package jade.content and its sub-packages. The package jade.content (and its sub-packages) allows to create application-specific ontologies and to use them independently of the adopted content language: the code that implements the ontology and the code that sends and receives messages do not depend on the content language. SIIT Master, University of Genoa Software Agents and MASs 51 / 84

65 Ontology and JADE Creating an Application-Specific Ontology An ontology defines a vocabulary and a set of relationships between the elements of the vocabulary. The relationships can be: 1 structural, e.g. the predicate fatherof is defined over two parameters, a father and a set of children because we want to use it to say fatherof(john, (Mary,Lisa)); 2 semantic, e.g., a concept belonging to the class Man also belongs to the class Person. SIIT Master, University of Genoa Software Agents and MASs 52 / 84

66 Ontology and JADE Creating an Application-Specific Ontology An application-specific ontology is implemented through one object of class jade.content.onto.ontology and it is characterized by: 1 one name; 2 one base ontology at most, i.e., an ontology that it extends; 3 set of element schemata. SIIT Master, University of Genoa Software Agents and MASs 53 / 84

67 Ontology and JADE Creating an Application-Specific Ontology An application-specific ontology is implemented through one object of class jade.content.onto.ontology and it is characterized by: 1 one name; 2 one base ontology at most, i.e., an ontology that it extends; 3 set of element schemata. Element schemas are objects describing the structure of concepts, actions, and predicates. For example, People ontology contains an element schema called Person. This schema states that a Person is characterized by a name and by an address SIIT Master, University of Genoa Software Agents and MASs 53 / 84

68 Ontology and JADE Creating an Application-Specific Ontology public class PeopleOntology extends Ontology { // The name of this ontology. public static final String ONTOLOGY_NAME = "PEOPLE_ONTOLOGY"; // Concepts, i.e., objects of the world. public static final String PERSON = "PERSON"; public static final String MAN = "MAN"; public static final String WOMAN = "WOMAN"; public static final String ADDRESS = "ADDRESS"; // Slots of concepts, i.e., attributes of objects. public static final String NAME = "NAME"; public static final String STREET = "STREET"; public static final String NUMBER = "NUMBER"; public static final String CITY = "CITY"; SIIT Master, University of Genoa Software Agents and MASs 54 / 84

69 Ontology and JADE Creating an Application-Specific Ontology // Predicates public static final String FATHER_OF = "FATHER_OF"; public static final String MOTHER_OF = "MOTHER_OF"; // Roles in predicates, i.e., names of arguments for predicates public static final String FATHER = "FATHER"; public static final String MOTHER = "MOTHER"; public static final String CHILDREN = "CHILDREN"; // Actions public static final String MARRY = "MARRY"; // Arguments in actions public static final String HUSBAND = "HUSBAND"; public static final String WIFE = "WIFE"; SIIT Master, University of Genoa Software Agents and MASs 55 / 84

70 Ontology and JADE Creating an Application-Specific Ontology private static PeopleOntology theinstance = new PeopleOntology(); public static PeopleOntology getinstance() { return theinstance; } public PeopleOntology(Ontology base) { super(ontology_name, ACLOntology.getInstance()); // Add definitions of schemata here.... } } SIIT Master, University of Genoa Software Agents and MASs 56 / 84

71 Ontology and JADE Creating an Application-Specific Ontology The definition of the ontology in the example is not complete, we have to substitute dots with the definition of the element schemata. Element schemata are objects describing the structure of concepts, actions, predicate, etc. that we allow in our messages. In the People ontology they describe what a person is, what an address is, what a father is, etc. The following is the element schema for the concept of Person. This schema states that a Person is characterized by a name and an address: SIIT Master, University of Genoa Software Agents and MASs 57 / 84

72 Ontology and JADE Creating an Application-Specific Ontology // Get the element schema for strings from BasicOntology PrimitiveSchema stringschema = (PrimitiveSchema)getSchema(BasicOntology.STRING); // Define the concept of Person ConceptSchema personschema = new ConceptSchema(PERSON); personschema.add(name, stringschema); personschema.add(address, addressschema, ObjectSchema.OPTIONAL); // Add the schema to the ontology add(personschema); // Define and add the concept of Man ConceptSchema manschema = new ConceptSchema(MAN); manschema.addsuperschema(personschema); SIIT Master, University of Genoa Software Agents and MASs 58 / 84

73 Ontology and JADE Creating an Application-Specific Ontology // Get the element schema for strings from BasicOntology PrimitiveSchema stringschema = (PrimitiveSchema)getSchema(BasicOntology.STRING); // Define the concept of Person ConceptSchema personschema = new ConceptSchema(PERSON); personschema.add(name, stringschema); personschema.add(address, addressschema, ObjectSchema.OPTIONAL); // Add the schema to the ontology add(personschema, Person.class); // Define and add the concept of Man ConceptSchema manschema = new ConceptSchema(MAN); manschema.addsuperschema(personschema); SIIT Master, University of Genoa Software Agents and MASs 59 / 84

74 Ontology and JADE Creating an Application-Specific Ontology public class Person extends Concept { private String name = null; private Address address = null; public void setname(string name) { this.name = name; } public void setaddress(address address) { this.address = address; } public String getname() { return name; } public Address getaddress() { return address; } } SIIT Master, University of Genoa Software Agents and MASs 60 / 84

75 Ontology and JADE Creating an Application-Specific Ontology // Add the schema to the ontology add(personschema, Person.class); In order to associate a class with a schema, the class must: 1 extend a class in jade.content, e.g., Person extends Concept because we want to associate it with a concept schema; 2 provide public get/set methods for each attribute (you can use basic types like int or boolean); 3 provide a constructor with no parameters, i.e., the default contructor. SIIT Master, University of Genoa Software Agents and MASs 61 / 84

76 Ontology and JADE Creating an Application-Specific Ontology // Define a schema for the set of children AggregateSchema childrenschema = new AggregateSchema(BasicOntology.SET); // Define the schema for fatherof predicate PredicateSchema fatherofschema = new PredicateSchema(FATHER_OF); fatherofschema.add(father, manschema); fatherofschema.add(children, childrenschema); // Add the predicate to the ontology add(fatherofschema, FatherOf.class); SIIT Master, University of Genoa Software Agents and MASs 62 / 84

77 Ontology and JADE Creating an Application-Specific Ontology public class FatherOf extends Predicate { private List children = null; private Man father = null; } public void setchildren(list children) { this.children = children; } public void setfather(man father) { this.father = father; } public Man getfather() { return father; } public List getchildren() { return children; } SIIT Master, University of Genoa Software Agents and MASs 63 / 84

78 Ontology and JADE Sending and Receiving Messages In order to send and receive messages, we need 1 an ontology to provides the vocabulary and 2 a codec (coder/encoder) to handle the syntax of the content language. These are registered with JADE through the content manager. The content manager provides methods for encoding and decoding the content of messages exploiting the registered ontologies and codecs. getcontentmanager().registerontology(peopleontology.getinstance()); getcontentmanager().registerlanguage(new JCodec()); SIIT Master, University of Genoa Software Agents and MASs 64 / 84

79 Ontology and JADE Sending and Receiving Messages In order to send a message, we have two possibilities: through concrete objects or through abstract descriptors. The first approach is the easiest to use, but it is limited: we create our content in terms of objects that belongs to the classes that we associated with schemas in the ontology, e.g., Person and FatherOf classes; we use fillcontent() in ContentManager to fill the content of the message. SIIT Master, University of Genoa Software Agents and MASs 65 / 84

80 Ontology and JADE Sending and Receiving Messages through concrete objects ACLMessage message = new ACLMessage(ACLMessage.INFORM); // Set the fields of the ACL message... // Create the concrete object representing the content Man john = new Man(); Man bill = new Man(); john.setname("john"); bill.setname("bill"); Address johnaddress = new Address(); johnaddress.setcity("london"); john.setaddress(johnaddress); Address billaddress = new Address(); billaddress.setcity("paris"); bill.setaddress(billaddress); SIIT Master, University of Genoa Software Agents and MASs 66 / 84

81 Ontology and JADE Sending and Receiving Messages through concrete objects FatherOf fatherof = new FatherOf(); fatherof.setfather(john); List children = new ArrayList(); children.add(bill); fatherof.setchildren(children); getcontentmanager().fillcontent(message, fatherof); SIIT Master, University of Genoa Software Agents and MASs 67 / 84

82 Ontology and JADE Sending and Receiving Messages through concrete objects FatherOf fatherof = new FatherOf(); fatherof.setfather(john); List children = new ArrayList(); children.add(bill); fatherof.setchildren(children); getcontentmanager().fillcontent(message, fatherof); For example, consider the following problem: we want to query an agent for the names of John s children. (iota?x fatherof(john,?x)) SIIT Master, University of Genoa Software Agents and MASs 67 / 84

83 Ontology and JADE Sending and Receiving Messages through abstract descriptors An abstract descriptor is an object that describes an instantiation of a schema, e.g., the following is the abstract descriptor that describes the concept John : AbsConcept absjohn = new AbsConcept(PeopleOntology.MAN); absjohn.set(peopleontology.name, "John"); SIIT Master, University of Genoa Software Agents and MASs 68 / 84

84 Ontology and JADE Sending and Receiving Messages through abstract descriptors ACLMessage message = new ACLMessage(ACLMessage.QUERY_REF); // Set the fields of the message... // Create the abstract descriptor representing the content AbsConcept absjohn = new AbsConcept(PeopleOntology.MAN); absjohn.set(peopleontology.name, "John"); AbsVariable absx = new AbsVariable("X") AbsPredicate absfatherof = new AbsPredicate(PeopleOntology.FATHER_OF); absfatherof.set(peopleontology.father, absjohn); absfatherof.set(peopleontology.children, absx); AbsIRE absire = new AbsIRE(absX, absfatherof); getcontentmanager().fillcontent(message, absire); SIIT Master, University of Genoa Software Agents and MASs 69 / 84

85 Ontology and JADE Sending and Receiving Messages ACLMessage msg = blockingreceive(aclmessage.inform); // The content of informs do not contain variables Proposition p = (Proposition)getContentManager().extractContent(msg); // Handle the content if(p instanceof FatherOf) {... } ACLMessage msg = blockingreceive(aclmessage.query_ref); // The content of query-refs do contain variables AbsIRE absire = (AbsIRE)getContentManager().extractAbsContent(msg); // Handle the content AbsVariable absx = absire.getvariable(); AbsProposition absp = absire.getproposition(); SIIT Master, University of Genoa Software Agents and MASs 70 / 84

86 Contents WordNet Definition 4 Semantic Web 5 Ontology Languages for the Semantic Web RDF DAML+OIL OWL 6 Ontology and JADE 7 WordNet Definition The WordNet ontology SIIT Master, University of Genoa Software Agents and MASs 71 / 84

87 WordNet Definition What is WordNet - Wikipedia Definition WordNet is a semantic lexicon for the English language. It groups English words into sets of synonyms called synsets, provides short, general definitions, and records the various semantic relations between these synonym sets SIIT Master, University of Genoa Software Agents and MASs 72 / 84

88 WordNet Definition What is WordNet - Wikipedia Definition WordNet is a semantic lexicon for the English language. It groups English words into sets of synonyms called synsets, provides short, general definitions, and records the various semantic relations between these synonym sets WordNet was created and is being maintained at the Cognitive Science Laboratory of Princeton University under the direction of psychology professor George A. Miller. Development began in Over the years, the project received about $3 million of funding, mainly from government agencies interested in machine translation. SIIT Master, University of Genoa Software Agents and MASs 72 / 84

89 Basic lexical relations: WordNet Definition Synonymy: is WordNet s basic relation. Synonymy is a symmetric relation between word forms. Homonymy: not related meaning; e.g. bank (river) and bank (financial institution) Hyponymy: (sub-name) and its inverse, Hypernymy (super-name), are transitive relations between synsets. Because there is usually only one hypernym, this semantic relation organizes the meanings of nouns into a hierarchical structure. SIIT Master, University of Genoa Software Agents and MASs 73 / 84

90 Basic lexical relations: WordNet Definition Antonymy: (opposing-name) is also a symmetric semantic relation between word forms, especially important in organizing the meanings of adjectives and adverbs. Meronymy: (part-name) and its inverse, Holonymy (whole-name), are complex semantic relations. WordNet distinguishes component parts, substantive parts, and member parts. Troponymy: (manner-name) is for verbs what hyponymy is for nouns, although the resulting hierarchies are much shallower. Entailment: relations between verbs are also coded in WordNet. SIIT Master, University of Genoa Software Agents and MASs 74 / 84

91 Basic lexical relations: WordNet Definition Semantic Relation Syntactic Category Examples Synonymy N,V,Aj,Av pipe,tube rise,ascend sad, unhappy rapidly, speedily Antonymy Aj,Av,(N,V) wet, dry powerful, powerless friendly, unfriendly rapidly, slowly Hyponymy N maple,tree tree, plant Meronymy N ship, fleet gin, martini Troponymy V march, walk whisper, speak Entailment V drive, ride divorce, marry SIIT Master, University of Genoa Software Agents and MASs 75 / 84

92 Contents WordNet The WordNet ontology 4 Semantic Web 5 Ontology Languages for the Semantic Web RDF DAML+OIL OWL 6 Ontology and JADE 7 WordNet Definition The WordNet ontology SIIT Master, University of Genoa Software Agents and MASs 76 / 84

93 WordNet The WordNet ontology The WordNet ontology lexical categories: (hierarchy) nouns (3-level hierarchy) verbs adjective and adverbs language: English #nouns: #synsets: #verbs: #adjectives: #adverbs: fine granularity (version 2.0) : too much? SIIT Master, University of Genoa Software Agents and MASs 77 / 84

94 The WordNet ontology WordNet The WordNet ontology Access to WordNet (data base of lexical relations): library functions on-line (browser): SIIT Master, University of Genoa Software Agents and MASs 78 / 84

95 WordNet The WordNet ontology The WordNet ontology - library functions Part Of Speech (POS): noun, verb, adj, adv index file: index.pos e.g. plant n 4 #m %s %p n: noun 4 senses 5 lexical relations: hypernymy, hyponymy, member of, substance of, part of synset addresses SIIT Master, University of Genoa Software Agents and MASs 79 / 84

96 WordNet The WordNet ontology The WordNet ontology - library functions data file: data.pos e.g n 03 plant 0 flora 0 plant life 0 n ? n 0000 a living organism lacking the power of locomotion n: noun 3: number of lexemes (0 separator) 27: number of lexical relations SIIT Master, University of Genoa Software Agents and MASs 80 / 84

97 WordNet The WordNet ontology The WordNet ontology - on the web SIIT Master, University of Genoa Software Agents and MASs 81 / 84

98 WordNet The WordNet ontology The WordNet ontology - library functions classpath (is-a relationship) of sense #7 of bass (the member with the lowest range of a family of musical instruments) SIIT Master, University of Genoa Software Agents and MASs 82 / 84

99 WordNet The WordNet ontology The WordNet ontology - versions EuroWordNet version (not available on-line) for different European languages: Spanish French German Dutch Czech Estonian Italian (CNR-Pisa)... MultiWordNet: Italian (IRST-Trento, B. Magnini) (available on-line SIIT Master, University of Genoa Software Agents and MASs 83 / 84

100 WordNet EuroWordNet vs MultiWordNet The WordNet ontology There are at least two models for building a multilingual wordnet. The first model, adopted within the EuroWordNet project, consists of building language specific wordnets independently from each other, trying in a second phase to find correspondences between them (Vossen, 1998). The second model, adopted within MultiWordNet (MWN), consists of building language specific wordnets keeping as much as possible of the semantic relations available in the Princeton WordNet (PWN). SIIT Master, University of Genoa Software Agents and MASs 84 / 84