1. Semantic Web for the Working Ontologist Dean Allemang Jim Hendler SNU IDB laboratory

2. Semantic Web for the Working OntologistDean Allemang, Jim Hendler Working Ontology Contents 2 ■ Chapter 1 What is the Semantic Web? ■ Chapter 2 Semantic Modeling ■ Chapter 3 RDF-The Basis of the semantic Web ■ Chapter 4 Semantic Web Application Architecture ■ Chapter 5 RDF and Inferencing ■ Chapter 6 RDF Schema ■ Chapter 7 RDFS-Plus ■ Chapter 8 Using RDFS-Plus in the Wild ■ Chapter 9 Basic OWL ■ Chapter 10 Counting and Sets in OWL ■ Chapter 11 Using OWL in the Wild ■ Chapter 12 Good and Bad Modeling Practices ■ Chapter 13 OWL Levels and Logic

3. Semantic Web for the Working OntologistDean Allemang, Jim Hendler Chapter 2 Semantic Modeling ■ 1. Modeling for Human Communication ■ 2. Explanation and Prediction ■ 3 Mediating Variability 3.1. Variation and Classes 3.2. Variation and Layers ■ 4. Expressivity in Modeling 3

4. Semantic Web for the Working OntologistDean Allemang, Jim Hendler Introduction ■ The Semantic Web Uses AAA Slogan, open world assumption, nonunique naming for Network Effect These ideas are good for Information gathering and sharing But they make confusion, disagreement, and conflict ■ Web infrastructure have to solve these problem for information sharing, cooperation and collaboration The answer is Modeling! 4 Semantic Web Modeling Confusion Disagreement Conflict Information sharing Cooperation Collaboration

5. Semantic Web for the Working OntologistDean Allemang, Jim Hendler Introduction: Modeling ■ Modeling is the process of organizing information for community use ■ Modeling supports this in three ways ■ 1) Framework for human communication (→Section 1) It allows people to collaborate on their understanding ■ 2) Explain and make predictions (→ Section 2) It helps individuals make their own judgments ■ 3) Structure for managing varying viewpoints (→ Section 3) It is essential to fostering understanding in a web environment 5

6. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Modeling for Human Communication 6 1) Framework for human communication It allows people to collaborate on their understanding 2) Explain and make predictions It helps individuals make their own judgments 3) Structure for managing varying viewpoints It is essential to fostering understanding in a web environment 3 Functions of Modeling

7. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Modeling for Human Communication ■ Human Communication is a goal for Modeling It is the fundamental requirement for building a Semantic Web It allows people to contribute to a growing body of knowledge and then draw from it 7 Semantic Web Model Human Communication contribute knowledge draw from it

8. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Modeling for Human Communication ■ Formality of Modeling There are 2 types of Model for Human Communication Formal Model, Informal Model ■ example 8 Informal ModelFormal Model private agreements National law

9. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Modeling for Human Communication ■ Informal Models Community tagging: a more collaborative style of document modeling 9 Community tagging style Informal Model It provides an informal organization to a large body of heterogeneous information

10. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Modeling for Human Communication ■ Heavily layered Models Informal model have the risk that its meaning will not be clear, so further modeling must be done to clarify that Further models are required to provide common context to explicate the shared meaning 10 Informal Model Informal Model Heavily Layered Models Because of the inherent ambiguity of natural language Need next layer of commentary Repeat until it clarifies the meaning

11. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Explanation and Prediction 11 1) Framework for human communication It allows people to collaborate on their understanding 2) Explain and make predictions It helps individuals make their own judgments 3) Structure for managing varying viewpoints It is essential to fostering understanding in a web environment 3 Functions of Modeling

12. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Explanation and Prediction ■ Models are used to organize human thought in the form of explanations ■ Explanation Explanation makes it easier to reuse a model in whole or in part Explanation relates a phenomenon to “first principles” ■ Formalism Objective form, and the rules that govern how it works Formal modes are the bread and butter of mathematical modeling 12 Formal Model Mathematical modeling Explanation

13. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Explanation and Prediction ■ Prediction Formalisms can also be used for predictions Given a description of a situation in some formalism, the same rules that govern transformations in proofs can be used to make predictions 13 Formal Modeling 1 + 2 = 3 Formal Modeling 1 + 1 = 2 1 + 1 + 1 = 3 Prediction

14. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Explanation and Prediction ■ Therefore, Formal modeling has vary different social dynamic than informal modeling Because there is an objective reference to the model(the formalism) There is no need for the layers of interpretation 14 Informal Model Heavily Layered Models Formal Model Informal ModelFormal Model Need layers of interpretation to avoid ambiguity vs Need to follow formalism for explanation and prediction

15. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3. Mediating Variability 15 1) Framework for human communication It allows people to collaborate on their understanding 2) Explain and make predictions It helps individuals make their own judgments 3) Structure for managing varying viewpoints It is essential to fostering understanding in a web environment 3 Functions of Modeling

16. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3. Mediating Variability ■ Variability The dynamics of the network effect require the ability to represent a variety of opinions A good model organizes those opinions so that the things that are common can be represented together, while the things that are distinct can be represented as well 16 IAU 8 planets astrologers 9 planets website 8 planets 9 planets

17. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3. Mediating Variability ■ Ways to accommodate these different view points ■ 1) Control the Web so that only that position is supported Where a small group or even a single person acts as the db admin Not appropriate for the Web because it does not allow for the AAA slogan 17 IAU 8 planets astrologer s 9 planets website 8 planets 9 planets admin

18. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3. Mediating Variability ■ 2) Allow each one to be represented separately, with no reference to one another at all Basis of an informal approach, and it indeed describes the state of the document web as it is today It would be the responsibility of the information consumer to understand Model must allow for each of these differing viewpoints to be expressed 18 website 8 planets website 9 planets astrologers 9 planets consumers IAU 8 planets

19. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.1. Variation and Classes ■ The Semantic Web standards also use this idea of class hierarchy for representing commonality and variability (OOP) Organizing commonality and variability in components But, Unlike OOP, Semantic Web isn’t focused on s/w representation ▶ Classes are not defined in terms of behaviors of functions But the notion of classes and subclasses remains, and it plays much the same role 19 High-level classes lower-level classes Represent commonality among a large variety of entities Represent commonality among a small, specific set of things

20. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.1. Variation and Classes: Examples ■ Solar System Body ■ The 2006 IAU definition of planet 1. It is in orbit around the sun 2. It has sufficient mass to be nearly round 3. It has cleared the neighborhood around its orbit ■ By IAU definition, Planet: satisfies conditions 1 + 2 + 3 Pluto(dwarf planet) : satisfies conditions 1 + 2 (not 3!) SSSB(small solar system body): satisfies condition 1 20 SSB IAU:Planet IAU

21. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.1. Variation and Classes: Examples ■ Twentieth-century astronomy Not quite as organized as IAU definition ■ Astrology Not quite as organized as IAU definition 21 astro:Planethoro:Planet astrologers SSB IAU:Planet astro:Planethoro:Planet

22. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.1. Variation and Classes: Examples ■ We can go further in this modeling when we observe that there are only eight IAU:Planets, and each one is also a horo:Planet and an astro:Planet ■ Thus, we can say that IAU:Planet is a subclass of both horo:Planet and astro:Planet ■ In this way, we can model the commonality among entities (at the high level) while respecting their variation (at a low level) 22 SSB astro:Planet horo:Planet IAU:Planet

23. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.2. Variation and Layers ■ If we can’t structure the entities they are describing into a class model? ■ The Semantic Web provides an elegant solution to this problem The basic idea is that any model can be built up from contributions from multiple sources The entire model is the combination of all the layers 23

24. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.2. Variation and Layers: Examples 24 RegenerationRebirthPluto NitrogenMethane signifies prefSymbol madeOf Information about Pluto of astrologersInformation about Pluto of astronomers

25. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3.2. Variation and Layers: Examples ■ The simplest way is to simply merge the two models into a single one that includes all the information from each model ■ But merging models has a draw back: machine can’t figure out inconsistency between “ prefSymbol” and “ prefSymbol” This is the reason why we need to publish models on the Semantic Web 25 Regeneration Rebirth Pluto Nitrogen Methane signifies prefSymbol madeOf

26. Semantic Web for the Working OntologistDean Allemang, Jim Hendler ■ Trade-off when we model People Need different tool: This difference is one of Level of expressivity ■ More expressive model is not superior one Different expressive model are just used for different purposes 4. Expressivity in Modeling 26 H2OH2OH O H least expressivemost expressive 1. Two (H), One (O) 2. It can break into (H), (OH) But not (HH) 1. Two (H), One (O) 2. It can break into (H), (OH) But not (HH) 3. Shows chemical & physical structure Simple, but widely used More expressive, but more complex

27. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 4. Expressivity in Modeling ■ The Semantic Web providing a number of modeling languages that differ in their level of expressivity 27 least expressivemost expressive RDF RDFSRDF-PLUSOWL

28. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 4. Expressivity in Modeling ■ RDF(Resource Description Framework) ch3, ch4, ch5 The basic framework providing a mechanism for ▶ Allowing anyone to make a basic statement about anything ▶ Layering these statements into a single model Having been a recommendation from the W3C since 2003 ■ RDFS(RDF Schema Language) ch6 A language with the expressivity ▶ to describe the basic notions of commonality and variability ▶ Familiar form object languages and other class systems-namely classes, subclasses, and properties RDFS has been a W3C recommendation since 2003 28

29. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 4. Expressivity in Modeling ■ RDF-PLUS ch7, ch8 A subset of OWL More expressive than RDFS Without the complexity of OWL ■ OWL(Web Ontology Language) ch9, ch10, ch11, ch12, ch13 Brings the expressivity of logic to the Semantic Web To allow modelers to express detailed constraints between classes, entities, and properties Being adopted as a recommendation by the W3C in 2003 29