TOP INTRO TO MULTIMEDIA NTWRK
TOP INTRO TO MULTIMEDIA NTWRK CS 410
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This 15 page Class Notes was uploaded by Orrin Rutherford on Wednesday September 2, 2015. The Class Notes belongs to CS 410 at Portland State University taught by Staff in Fall. Since its upload, it has received 12 views. For similar materials see /class/168283/cs-410-portland-state-university in ComputerScienence at Portland State University.
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Date Created: 09/02/15
Example Taxonomy of Organisms Hierarchy of categories Kingdom phylum class order family genus species Chordates Arthropods Vertebrates I insects I I spiders I Icrustaceans I birds I I reptiles I ImammalsI How would you design a relational schema for this Relational Schema for Taxonomy Adjacency list Idea each tuple has a parent id name Parentid Animal null Chordates Animal Arthropods Animal Vertebrates Chordates Insects Arthropods Spiders Arthropods Birds Vertebrates Reptiles Vertebrates Problem Recursive Queries Find all ancestorsdescendants of X Find all arthropods that are not crustaceans Print the whole tree Solutions may require many lines of code and may not be very robust Another Solution nested sets Idea traverse entire tree assign each object in tree a eftid and a rightid Each child eftid and rightid are between parent s eftid and rightid Label entire tree using depthfirst traversal of tree Nested sets example Animals Chordates 11 Arthropods vertEbrates I insects I I spiders I Icrustaceans 2 00 4I birds I56I reptiles I7 8ImammalsI9 name Leftid Rightid Animal 1 20 Chordates 2 11 Vertebrates 3 10 Birds 4 5 Challenges Need a script to traverse database Script must be rerun every time database is updated Update time linear in size of table More costly than Btrees Multidimensional Arrays How would you store an array in a database One option x y 2 values as columns A512 253 becomes x y 2 value 5 1 2 253 Problems High storage overhead each index is now stored as an integer value Queries more complex Lose proximity information what is near an array element Iterating over arrays takes longer A512 and A513 may not be stored near each other Should I use a RDBMS Advantages Leverage years of research and practice Eg indexes query optimization Many commercial and opensource products available Should I use a RDBMS Disadvantages May be difficult to express dataqueries using relational model eg arrays hierarchical data Performance issues Need to consider these tradeoffs Welldesigned database can help Augment database to support domain Chapter 3 What are OWL Ontologies Ontologies are used to capture knowledge about some domain of interest An ontology describes the concepts in the domain and also the relationships that hold between those concepts Di erent ontology languages provide di erent facilities The most recent development in standard ontology languages is OWL from the World Wide Web Consortium WSC1i Like Prot g OWL makes it possible to describe concepts but it also provides new facilities It has a richer set of operators eigi and7 or and negationi It is based on a di erent logical model which makes it possible for concepts to be de ned as well as described Complex concepts can therefore be built up in de nitions out of simpler concepts Furthermore7 the logical model allows the use of a reasoner which can check whether or not all of the statements and de nitions in the ontology are mutually consistent and can also recognise which concepts t under which de nitions The reasoner can therefore help to maintain the hierarchy correctly This is particularly useful when dealing with cases where classes can have more than one parent 31 The Three Species Of OWL OWL ontologies may be categorised into three species or sub languages OWLLite7 OWLDL and OWL Fulli A de ning feature of each sub language is its expressiveness OWLLite is the least expressive sub langaugei OWLFull is the most expressive sub languagei The expressiveness of OWLDL falls between that of OWLLite and OWLFull OWLDL may be considered as an extension of OWLLite and OWLFull an extension of OWLDLi 311 OWLLite OWLLite is the syntactically simplest sub languagei It is intended to be used in situations where only a simple class hierarchy and simple constraints are needed For example7 it is envisaged that OWLLite will provide a quick migration path for existing thesauri and other conceptually simple hierarchies 1httpwwwrwSrorgTRowliguide 312 OWLDL OWLDL is much more expressive than OWLLite and is based on Descm ption Logics hence the suf x DL Description Logics are a decidable fragment of First Order Logic2 and are therefore amenable to automated reasoning It is therefore possible to automatically compute the classi cation hierarchy8 and check for inconsistencies in an ontology that conforms to OWLDL This tutorial focuses on OWL DL 313 OWLFull OWLFull is the most expressive OWL sublanguage It is intended to be used in situations where very high expressiveness is more important than being able to guarantee the decidability or computational completeness of the language It is therefore not possible to perform automated reasoning on OWLFull ontologies 314 Choosing The SubLanguage To Use For a more detailed synopsis of the three OWL sub languages see the OWL Web Ontology Language Overview4 Although many factors come into deciding the appropriate sub language to use there are some simple rules of thumb o The choice between OWLLite and OWLDL may be based upon whether the simple constructs of OWLLite are suf cient or not 0 The choice between OWLDL and OWLFull may be based upon whether it is important to be able to carry out automated reasoning on the ontology or whether it is important to be able to use highly expressive and powerful modelling facilities such as metaclasses classes of classes The Prot g OWL plugin does not make the distinction between editing OWLLite and OWLDL on tologies It does however offer the option to constrain the ontology being edited to OWLDL or allow the expressiveness of OWLFull 7 See section 71 for more information on how to constrain the ontology to OWLDL 32 Components of OWL Ontologies OWL ontologies have similar components to Prot g frame based ontologies However the terminology used to describe these components is slightly different from that used in Prot g An OWL ontology consists of Individuals Properties and Classes which roughly correspond to Prot g lnstances Slots and Classes 2Logiee are decidable if computationsalgorithms based on the logic will terminate in a nite time 3Also known as anbanmptz an reasoning 4httpwwww3orgTRow1efeatures O E d 0 Italy ng an 0 USA W0 0 Fluffy ltgt Gemma ltgt Fido Matthe Figure 31 Representation Of Individuals 321 Individuals Individuals represent objects in the domain that we are interested in5 An important di erence between Prot g and OWL is that OWL does not use the Unique Name Assumption This means that two different names could actually refer to the same individual For example Queen Elizabeth The Queen and Elizabeth Windsor might all refer to the same individual In OWL it must be explicitly stated that individuals are the same as each other or different to each other 7 otherwise they might be the same as each other or they might be di erent to each other Figure 31 shows a representation of some individuals in some domain 7 in this tutorial we represent individuals as diamonds in diagrams Vocabulary Individuals are also known as instances Individuals can be referred to as being instances of classes 322 Properties Properties are binary relations6 on individuals ie properties link two individuals together7 For example the property hasSiinng might link the individual Matthew to the individual Gemma or the property hasChild might link the individual Peter to the individual Matthew Properties can have inverses For example the inverse of hasOWner is isOWnedBy Properties can be limited to having a single value 7 ie to being functional They can also be either transitive or symmetric These property characteristics are explained in detail section 48 Figure 32 shows a representation of some properties linking some individuals together Vocabulary Properties are roughly equivalent to slots in Prot g They are also known as roles in description logics and relations in UML and other object oriented notions In GRAIL and some other formalisms they are called attributes 5Also known as the domain of discourse 6A binary relation is a relation between two thin s 7Strictly speaking we should speak of instances of properties7 linking individuals but for the sake of brevity we will keep it simple England 425 Matthewltgt hasSiblin Gemma Figure 32 Representation Of Properties Figure 33 Representation Of Classes Containing Individuals 323 Classes OWL classes are interpreted as sets that contain individuals They are descm bed using formal math ematical descriptions that state precisely the requirements for membership of the class For example the class Cat would contain all the individuals that are cats in our domain of interest8 Classes may be organised into a superclass subclass hierarchy which is also known as a taxonomy Subclasses specialise are subsumed by their superclasses For example consider the classes Animal and Cat 7 Cat might be a subclass of Animal so Animal is the superclass of Cat This says that All cats are animals All members of the class Cat are members of the class Animal Being a Cat implies that you re an Animal and Cat is subsumed by Animal s One of the key features of OWLDL is that these superclass subclass relationships subsumption relationships can be computed automatically by a Teosoner 7 more on this ateri Figure 33 shows a representation of some classes containing individuals 7 classes are represented as circles or ovals rather like sets in Venn diagrams Vocabulary The word concept is sometimes used in place of class Classes are a concrete A representation of concepts In OWL classes are built up of descriptions that specify the conditions that must be satis ed by an individual for it to be a member of the class How to formulate these descriptions will be explained as 81ndividuals may belong to more than one class the tutorial progresses
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