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the development complexity is increased, and the usability of the tools is reduced. Finally, only the KB framework supports deduction and update of the knowledge with dedicated components and design patterns. The last table category summarizes the architectural aspects of the tools. All the tools have methodological support, but except the KB framework, they are difficult to extend mainly because they base on two-tier architecture. The KB framework is open to extensibility by means of custom units. Extensions may occur either at the framework logic level providing a new functionality upon the existing inference system, at the business logic level giving access to the knowledge base, or at both. In Table 6.2 a second comparison is made upon the expressive power of knowledge representation languages (OWL and the language underlying the KB Framework). Both languages are mapped to formalisms from the Description Logics family. Such comparison focuses on the main features of each language in knowledge modeling in order to highlight their differences and their limitations. All of them support the notion of class and class hierarchy; although the KB Framework Language does not support exhaustive decomposition and partitioning, due to implementation problems encountered using Pellet. In fact, UML considers completeness upon generalization sets; therefore, we plan to resolve this limitation in future releases. Similar is the support of property hierarchies in the languages. Derived support indicates that the language does not provide a construct for the feature in question, but it supports it through a combination of other constructs. Attributes that characterize the class are covered through workarounds: both in OWL and in the KB Framework Language, class attributes are defined once in the class definition for all the instances of the class. Finally, enumeration of classes is not yet supported in KB Framework Language, although it is provided in UML. We plan to extend the implementation to cover this aspect too. 90
OWL DL KB Framework CLASS HIERARCHIES subclass Yes Yes Yes disjointness Yes Yes Yes completeness Yes Yes No partition Yes Yes No PROPERTY HIERARCHIES subproperty Yes Yes Yes disjointness Yes Yes Yes completeness Yes Yes No partition Derived Yes No OTHER FEATURES instance attributes class attributes cardinality constraints instance enumeration of classes Yes Yes Yes Workaround Yes Workaround Yes Yes Yes Yes Yes Yes Yes Yes No Table 6.2: Comparison of knowledge-representation languages expressive power 91
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POLITECNICO DI MILANO V Facoltà di
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Table of Contents Abstract ........
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1. Introduction At present the Web
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• Definition of the formal repres
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This approach overcomes the develop
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Both the teleological and the ontol
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consists of a data schema, describi
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high-level business rules, written
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Thanks to the automatic generation
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2.4.2 RDF Resource Description Fram
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Third, besides the aforementioned r
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The XMI serialization of UML [33] e
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2.9.2.1 Pellet Pellet 1 [47] is an
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3. Semantics Web based Recommendati
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them by invoking respectively the c
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etrieves the properties by their ca
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Figure 3.6: Instance Component 3.1.
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3.1.8 Add Components The Add compon
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Add Class Component ClassDisjointOf
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Page 43 and 44: Figure 3.17: Remove Datatype Compon
Page 45 and 46: 3.1.19 Remove Instance component Th
Page 47 and 48: 3.2.4 Export-XMI-from-KB component
Page 49 and 50: 3.3.1.2 Properties of a class patte
Page 51 and 52: 3.3.1.5 Instances of a class assumi
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Page 55 and 56: 3.3.2.2 Remove property value for a
Page 57 and 58: 3.4.2 Application Specification In
Page 59 and 60: Action • View Notification: Group
Page 61 and 62: Send Group Invitation Actor: Group
Page 63 and 64: A user can recommend friend as Frie
Page 65 and 66: In the figure 3.37, a User browsing
Page 67 and 68: Through the entry unit in figure 4.
Page 69 and 70: Figure 4.2: Example of WebML hypert
Page 71 and 72: Description Classes Hierarchy Unit
Page 73 and 74: Add PropertyValueAxiom Input: manda
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Page 77 and 78: page otherwise it will go to the er
Page 79 and 80: We are showing current user’s inf
Page 81 and 82: current user is sending a friend in
Page 83 and 84: The information of a particular gro
Page 85 and 86: Figure 4.20: HTML view to Post New
Page 87 and 88: the application domain as extended
Page 89: Knowledge Instances Yes Yes Yes Yes
Page 93 and 94: of a specific group members of the
Page 95 and 96: [22] OMG UML (2007), Unified Modeli
Page 97: [56] BRAMBILLA, M., CERI, S., FRATE
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