Semantics & data mining & document processing

1. Semantics & data mining & document processing Nima Kaviani School of Interactive Arts and Technology Simon Fraser University - SURREY

2. Towards Semantic Web Mining[5] • The idea is to combine two fast-developing research areas, Semantic Web, and Web Mining. • Semantic Web can be used to improve the results of web mining by exploiting new semantic structures in the web • Web mining is useful to enhance the concepts and instances by learning the definition of structures for knowledge organization and to provide the population of such knowledge organization

3. Web Mining • Definition: the application of data mining techniques to the content, structure and usage of web resources • Web Content Mining: a form of text mining to extract data from content of the web page • Web Structure Mining: extracts information reside in the structure of hypertext (the idea behind links and also the usage for page rankings) • Web Usage Mining: the web resource that is being mined is the record of the requests made by the user to capture the user behaviors

4. Semantic Web • Definition: to add semantic annotation to web documents so that they can be easily understand by human and read by machines for further inferences • Ontology Learning: semi-automatic extraction of semantics from the web to create an ontology. • Mapping and Merging Ontologies: to merge different ontologies and build a new domain specific ontology (described by Davis) • Instance Learning: automatic or semi-automatic methods to extract information from web-related documents, either to help in annotating new documents or to extract additional information from existing unstructured or partially structured documents.

5. Creating an Ontology • Ontology is a conceptualization of domain into human understandable but machine readable formats. A quadruple of entities, attributes, relationships and axioms. [3] • Steps in creating an ontology for the data [8]: • determining the scope of the ontology • reusing existing Ontologies • enumerating all the concepts needed • defining the taxonomy • defining the properties • defining facets of the concepts • defining instances Are normally Performed by Ontology Engineer Can be performed semi-automatically

6. Ontology Learning • Why do we try to make the ontology learning automatic (semi-automatic)? • The source data is usually stored as unstructured, semi-structured (HTML, XML) or structured (Data Bases) format and should be processed in order to be used in creating the ontology[3]. • Laborious and cumbersome task • Time consuming • Dynamic nature of available domains • Lack of tools and guidelines [1]

7. Semi-Automatic Ontology Learning • It aims to integrate multitude of disciplines in order to facilitate the construction of Ontologies[12]. because of tacit information available, human intervention is always required [5]. • Steps in Building an ontology automatically • Acquisition of concepts • Establishment of concept taxonomies • Discovering of non-taxonomic conceptual relations • Pruning the generated ontology

8. Acquisition of concepts and establishing taxonomic relations • Using IR and NLP techniques, concepts can be extracted quite efficiently. • Techniques are normally a combination of methods below with a tendency to consider one of them more effectively. • Computational Linguistic • Information Retrieval

9. Methods used in acquiring the concepts-1 Computational linguistic approach • Pre-processing the text to extract dependencies and single-word nouns • POS-tagger [11] (part-of-speech dependency parser) [2, 4] • Minipar (State-of-the-art dependency) [1] • Extracting multi-word noun phrases [2] • Shallow parse the text • Filter out word phrases with interesting POS-tag patterns • Decide for each phrase whether it is a noun phrases • Extracting taxonomical relations[14] • Uses regular expressions to find ISA relations • Defining regular expression relations like: • NP {, NP}* {,} or other NP • Bruises, wounds, broken bones, or other injuries • The overall process is a combination of the tools below[12] • Tokenizer: Regular expressions to find nouns • Lexicon: as a big repository for stems • Lexical analyzer: mixes results from the two methods above and extracts new concepts • Chunk parse: works on phrases to generate syntactic dependency relations-uses POS-tagger. • Heuristics: includes correlations beside linguistic-base dependency relations. • more terms • Low precision • High recall (it’s more important in learning) • Regular expressions to extract taxonomies

10. Methods used in acquiring the concepts-2 An information retrieval method using term weightings [12] • Counting relevant terms and extract the more frequent ones as concepts • lefl,d: the frequency of appearance of term l in the document d • dfl: the number of documents in the corpus D that term l occurs in • cfl: the total number of occurrences of term l in the corpus D • Methods to find the taxonomy • Clustering (starts from scratch and uses distributional data about words) • Classification (uses an available hierarchy and refines it) • Lexico-Syntactic (regular expressions)

11. Methods used in acquiring the concepts-3 Combines information extraction with Ontologies and bootstraps[9] • ontology is used to improve the quality of extraction • extracted information is used to improve the ontology • the idea is to use indicative terms to find informative terms and then to use informative terms to find new indicators • it is trying to extract a pattern to make indicators and informative concepts relevant

12. Methods used in acquiring the concepts-4 Specific purpose concept and taxonomy extraction [7] • Methodology: neighborhood of initial keywords • The anterior word of a word classifies it (in English) • The posterior word of a word represents the domain (in English) • coronary heart disease • Sends the query to the search engine and extracts anterior and posterior words of a word and decides on if the word is an instance or subclass. • Clustering is performed according to the coincidence amount • Synonymy is satisfied by using constraints and omitting the initial word

13. Current Status • Results • IR and Computational Linguistic can solve the problem • Current methods are trying to derive concepts and form taxonomical relations using the biggest available corpus, World Wide Web. • Problems to be solved • Current efforts are mostly using hand-crafted concept hierarchies • Hardly can find synonyms for a set of available concepts. • Hardly can make the process of discovering synonyms automatic using currently found synonyms

14. Establishment of non-taxonomic relations between concepts • The most important and challenging task in building an ontology. • Finding data concepts and taxonomic relations are simpler in comparison to construct non-taxonomic relation between concepts. • These approaches are generally a combination of Natural Language Processing and Machine Learning

15. Methods proposed to establish relations-1 Clustering [13] • ASIUM: a software designed based on unsupervised clustering method • Does not require any annotation of texts by hand • Learns knowledge in the form of • Subcategorization frames • <to travel> <subject: human> <by: vehicle> • subject is the syntactic role • by is the proposition • human and vehicle are restrictions of their selection • Ontologies

16. Methods proposed to establish relations-1 • Pre-Processing the text • SYLEX provides training text which is attachment of verbs to noun phrases and clauses. • The first step is done by getting the training text as input and generating instantiated Subcategorization frames as output. • <verb> • <subject> • <object>

17. Methods proposed to establish relations-1 • Clustering Algorithm • Factorizing similar instantiated subcategorization frames • Clustering algorithm used in ASIUM • Links represent generality relations • Breadth-First • Bottom-up clustering • Two classes are aggregated • Distance is defined as the portion of common head words in the two clusters taking into account their frequencies • Clusters with a distance less than the threshold are aggregated • The threshold doesn’t change in different levels • Available clusters, only in the same level, are taken into account

18. Methods proposed to establish relations-1 • card(c1) and card(c2): the number of different head words in cluster C1 and C2 • Ncomm the number of different common head words between C1 and C2 • is the sum of the frequencies of the head words of Cj • wordiCj is the i-th head word of cluster Cj • f(wordiCj) is its frequency • minimizes the influences of word frequencies

19. Methods proposed to establish relations-1 • This generality results in change of instantiated Subcategorization frames into Subcategorization frames • Cooperation of user in the process of building the ontology is required • User labels the clusters • User validates the new clusters • Rejects those words that restrict the given verbs • Partitions new clusters into sub-clusters which would not have been identified before • Clusters in each level must get validated before proceeding to the next level • User can partition the clusters and label sub-concepts if he find the newly generated classes useless or meaningless

20. Example father neighbor father mother Passenger Subjects verbs travel drive proposition using by by Objects train motorbike car car bicycle factorizing car, train, motorbike car, bicycle car, train, motorbike, bicycle clustering Motorized vehicle

21. Methods proposed to establish relations-2 Generalized association rules [10] • A set of transactions are defined • Each transaction consists of a set of items where each item is from a set of concepts • Two factors are considered in estimating amount of relevancy of two different concepts Xkand Ykin an association rule: • Support: percentage of transactions that contain Xkand Ykas a subset • Confidence: percentage of transactions that Ykis seen when Xkappears in a transaction • Some changes have been applied to the basic association rule algorithm to make it suitable for associations at the right level of the taxonomy

22. Methods proposed to establish relations-3 Fuzzy Formal Concept Analysis (FFCA)[3] • FCA is based on lattice theory and is used for conceptual knowledge discovery • Hierarchical relationship of concepts is organized as a lattice rather than a tree • The method uses a citation database to generate concepts • Steps in generating ontology using this method are: • FFCA • Concept Clustering • Ontology generation

23. Current Status • Results • Methods proposed have reduced the amount of effort by a human engineer • Problems to be solved • They all consider a single-layer generalization, however, in many case a multi-layer generalization would result in a better hierarchy • Still human plays a key role in designing the ontology and the quality of the design depends on his works

24. Pruning the generated hierarchy • The generated ontology contains concepts that are not interesting and should be removed. • Methods used to remove uninteresting nodes are: • Using a rule based method according to the following condition [6] • Nodes without a domain node are removed • Intermediate nodes with the following properties are removed • Nodes without siblings • It’s not the root of any concept • Conditions which are held in the ontology • Using IR techniques[12] • Considering term frequencies, comparing the frequency of the current term with the frequency in a generic corpus, and removing the term if its frequency in the domain is lower than that of the term in a generic corpus

25. Conclusion • A progress in building ontologies with web-pages rather than static texts as their instances is seen. • There is not a clear and defined way to evaluate automatically built ontologies and these ontologies are compared with hand-crafted ones. • The above fact hampers the comparison between two semi-automatically built ontologies

26. References • Sabou, M., Wroe, C., Goble, C., and Mishne, G. Learning domain ontologies for Web service descriptions: an experiment in bioinformatics. In Proceedings of the 14th international Conference on World Wide Web (Chiba, Japan, May 10 - 14, 2005). WWW '05. ACM Press, New York, NY, 2005. • van Hage, W. R., de Rijke, M., Marx M., Information Retrieval Support for Ontology Construction and Use. In Proceedings of the 3rd International Semantic Web Conference, Jan 2004, Pages 518 – 533, LNCS, Springer 2004. • Quan, T. T. , Hu,i S. C., Fong, A.C.M., Cao, T. H. Automatic Generation of Ontology for Scholarly Semantic Web. In Proceedings of the 3rd International Semantic Web Conference, Jan 2004, Pages 726 – 740, LNCS, Springer 2004. • Sabou, M., Wroe, C., Goble, C., and Mishne, G. Learning domain ontologies for Web service descriptions: an experiment in bioinformatics. In Proceedings of the 14th international Conference on World Wide Web (Chiba, Japan, May 10 - 14, 2005). WWW '05. ACM Press, New York, NY, 2005. • Berendt, B., Hotho, A., and Stumme, G. Towards semantic web mining. In I. Horrocks and J. Hendler (Eds.), The Semantic Web - ISWC 2002. In Proceedings of the 1st International Semantic Web Conference, June 9-12th, 2002, Sardinia, Italy, pages 264--278. LNCS, Heidelberg, Germany: Springer, 2002.

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