Semantic Word Clouds

Transcription

1 Seman&c Analysis in Language Technology Semantic Word Clouds Marina San(ni Department of Linguis(cs and Philology Uppsala University, Uppsala, Sweden Spring 2016

2 Previous lecture: Ontologies 2

3 Semantic Web & Ontologies The goal of the Seman(c Web is to allow web informa(on and services to be more effec(vely exploited by humans and automated tools. Essen(ally, the focus of the seman(c web is to share data instead of documents. This data must be meaningful both for human and for machines (ie automated tools and web applica(ons) Q: How are we going to represent meaning and knowledge on the web? A: via annota&on. Knowledge is represented in the form of rich conceptual schemas/formalisms called ontologies. Therefore, ontologies are the backbone of the Seman(c Web. Ontologies give formally defined meanings to the terms used in annota&ons, transforming them into seman&c annota&ons. 3

4 concepts that are hierarchically organized Ontologies are Tree of Porphyry, III AD Wordnet, XXI AD (see Lect 5, ex similarity measures) 4

5 Reasoning: RDF/OWL vs Databases (and other data structures) OWL axioms behave like inference rules rather than database constraints.! Class: Phoenix!!SubClassOf: ispetof only Wizard!! Individual: Fawkes! Types: Phoenix! Facts: ispetof Dumbledore! Fawkes is said to be a Phoenix and to be the pet of Dumbledore, and it is also stated that only a Wizard can have a pet Phoenix. In OWL, this leads to the implica(on that Dumbledore is a Wizard. That is, if we were to query the ontology for instances of Wizard, then Dumbledore would be part of the answer. In a database se[ng the schema could include a similar statement about the Phoenix class, but in this case it would be interpreted as a constraint on the data: adding the fact that Fawkes ispetof Dumbledore without Dumbledore being already known to be a Wizard would lead to an invalid database state, and such an update would therefore be rejected by a database management system as a constraint viola(on. 5

6 So, what is an ontology for us? An ontology is a FORMAl, EXPLICIT specifica&on of a SHARED conceptualiza&on Machine-readable Consensual Knowledge Concepts, properties relations, functions, constraints, axioms, are explicitly defined Abstract model and simplified view of some phenomenon in the world that we want to represent Studer, Benjamins, Fensel. Knowledge Engineering: Principles and Methods. Data and Knowledge Engineering. 25 (1998) An ontology is an explicit specification of a conceptualization 6 Gruber, T. A translation Approach to portable ontology specifications. Knowledge Acquisition. Vol

7 How to build an ontology Generally speaking (and roughly said), when designing an ontology, four main components are used: 1. Classes 2. Rela(ons 3. Axioms 4. Instances 7

8 Prac(cal Ac(vity: emo(ons Your remarks: Emo(ons are ambiguous: eg. happiness can be also ill- directed The polarity of some emo(ons cannot be assessed etc. Classes Rela(ons Axioms Instances etc. 8

9 Occupa(onal psychology (wikipedia) Industrial and organiza(onal psychology (also known as I O psychology, occupa(onal psychology, work psychology, WO psychology, IWO psychology and business psychology) is the scien$fic study of human behavior in the workplace and applies psychological theories and principles to organiza(ons and individuals in their workplace. I- O psychologists are trained in the scien(st prac((oner model. I- O psychologists contribute to an organiza(on's success by improving the performance, mo(va(on, job sa(sfac(on, occupa(onal safety and health as well as the overall health and well- being of its employees. An I O psychologist conducts research on employee behaviors and a[tudes, and how these can be improved through hiring prac(ces, training programs, feedback, and management systems. 9

10 In summary Why to build an ontology? To share common understanding of the structure of informa(on among people or machines To make domain assump$ons explicit Ojen based on controlled vocabulary To analyze domain knowledge To enable reuse of domain knowledge 10

11 Ontologies and Tags Ontologies and tagging systems are two different ways to organize the knowledge present in Web. The first one has a formal fundamental that derives from descrip(ve logic and ar(ficial intelligence. Domain experts decide the terms. The other one is simpler and it integrates heterogeneous contents, and it is based on the collabora(on of users in the Web 2.0. User- generated annota(on. 11

12 Folksonomies Tagging facili(es within Web 2.0 applica(ons have shown how it might be possible for user communi$es to collabora$vely annotate web content, and create simple forms of ontology via the development of loosely- hierarchically organised sets of tags, onen called folksonomies. 12

13 Folksonomy=Social Tagging Folksonomies (also known as social tagging) are user- defined metadata collec(ons. Users do not deliberately create folksonomies and there is rarely a prescribed purpose, but a folksonomy evolves when many users create or store content at par(cular sites and iden(fy what they think the content is about. Tag clouds pinpoint the frequency of certain tags. 13

14 A common way to organize tags is in tag clouds 14

15 Automa(c folksonomy construc(on The collec(ve knowledge expressed though user- generated tags has a great poten(al. However, we need tools to efficiently aggregate data from large numbers of users with highly idiosyncra$c vocabularies and invented words or expressions. Many approaches to automa(c folksonomy construc(on combine tags using sta(s(cal methods... Ample space for improvement 15

16 Ontology, taxonomy, folksonomy, etc. Many different defini(ons A good summary and interpreta(on is here: hpp:// ontologies

17 Today We will talk more generally about word clouds 17

18 Further Reading Seman&c Similarity from Natural Language and Ontology Analysis by Sébas(en Harispe, Sylvie Ranwez, Stefan Janaqi, and Jacky Montmain Synthesis Lectures on Human Language Technologies, May 2015, Vol. 8, No. 1 The two state- of- the- art approaches for es(ma(ng and quan(fying seman(c similari(es/relatedness of seman(c en((es are presented in detail: the first one relies on corpora analysis and is based on Natural Language Processing techniques and seman(c models while the second is based on more or less formal, computer- readable and workable forms of knowledge such as seman(c networks, thesauri or ontologies. 18

19 Previous lecture: the end 19

20 Acknowledgements This presenta(on is based on the following paper: Barth et al. (2014). Experimental Comparison of Seman(c Word Cloud. In Experimental Algorithms, Volume 8504 of the series Lecture Notes in Computer Science pp Link: hpps:// Some slides have been borrowed from Sergey Pupyrev. 20

21 Today Experiments on seman&cs- preserving word clouds, in which seman(cally related words are close to each other. 21

22 Outline What is a Word Cloud? 3 early algorithms 3 new algorithms Metrics & Quan(ta(ve Evalua(on 22

23 Word Clouds Word clouds have become a standard tool for abstrac(ng, visualizing and comparing texts We could apply the same or similar techniques to the huge amonts of tags produced by users interac(ng in the social networks 23

24 Comparison & conceptualiza(on Tool Word Clouds as a tool for conceptualizing documents. Cf Ontologies Ex: 2008, comparison of speeches: Obama vs McCain Cf. Lect 10: Extrac(ve summariza(on & Abstrac(ve summariza(on 24

25 Word Clouds and Tag Clouds are ojen used to represent importance among terms (ex, band popularity) or serve as a naviga(on tool (ex, Google search results). 25

26 The Problem How to compute seman(c- preserving word clouds in which seman(cally- related words are close to each other? 26

27 Wordle hpp:// Prac(cal tools, like Wordle, make word cloud visualiza(on easy. They offer an appealing way to SUMMARIZE text Shortoming: they do not capture the rela(onships between words in any way since word placement is independent of context 27

28 Many word clouds are arranged randomly (look also at the scapered colours) 28

29 Paperns and Vicinity/Adjacency Humans are spontaneously papern- seekers: if they see two words close to each other in a word cloud, they spontaneously think they are related 29

30 In Linguis(cs and NLP This natural tendency in linking spacial vicinity to seman&c relatedness is exploited as evidence that words are seman(cally related or seman(cally similar Remember? : You shall know a word by the company it keeps (Firth, J. R. 1957:11) 30

31 So, it makes sense to place such related words close to each other (look also at the color distribu(on) 31

32 Seman(c word clouds have higher user sa(sfac(on compared to other layouts 32

33 All recent word cloud visualiza(on tools aim to incoprorate seman(cs in the layout 33

34 but none of them provide any guarantee about the quality of the layout in terms of seman(cs 34

35 Early algorithms: Force- Directed Graph Most of the exis(ng algorithms are based on force- directed graph layout. Force- directed graph drawing algorithms are a class of algorithms for drawing graphs in an aesthe(cally pleasing way Aprac(ve forces between pairs to reduce empty space Repulsive forces ensure that words do not overlap Final force preserve seman(c rela(ons between words. Some of the most flexible algorithms for calcula(ng layouts of simple undirected graphs belong to a class known as force- directed algorithms. Such algorithms calculate the layout of a graph using only informa(on contained within the structure of the graph itself, rather than relying on domain- specific knowledge. Graphs drawn with these algorithms tend to be aesthe(cally pleasing, exhibit symmetries, and tend to produce crossing- free layouts for planar 35 graphs.

36 Newer Algorithms: rectangle representa(on of graphs Vertex- weighted and edge- weighed graph: The ver(ces of the graph are the words Their weight correspond to some measure of importance (eg. word frequencies) The edges capture the seman(c relatedness of pair of words (eg. co- occurrence) Their weight correspond to the strength of the rela(on Each vertex can be drawn as a box (rectangle) with a dimension determing by its weight A realized adjacency is the sum of the edge weights for all pairs of touching boxes. The goal is to maximize the realized adjacencies. 36

37 Purpose of the experiments that are shown here: Seman(cs preserva(on in terms of closeness/ vicinity/adjacency 37

38 Example A contact of 2 boxes is a common boundary. The contact of two boxes is interpredet as seman(c relatedness The contact of 2 boxes can be calculated, so the adjacency can be computed and evaluated. 38

39 Preprocessing: 1) Term Extrac(on 2) Ranking 3) Similarity/Dissimilarity Computa(on 39

40 Similarity/dissimilarity matrix 40

41 cos( v, w) = Lect 6: Repe((on v w v w = v w w v = Which pair of words is more similar? cosine(apricot,informa(on) = N i=1 N 2 v i=1 i v i w i N 2 w i i=1 large data computer apricot digital informa(on = =.16 cosine(digital,informa(on) = = =.58 cosine(apricot,digital) = = 0 41

42 Lect 06: Other possible similarity measures 42

43 Input - Output The input for all algorithms is a collec(on of n rectangles, each with a fixed width and height propor(onal to the rank of the word A similarity/dissimilarity matrix The output is a set of non- overlapping posi(ons for the rectangles. 43

44 Early Algorithms 1. Wordle (Random) 2. Context- Preserving Word Cloud Visualiza(on (CPWCV) 3. Seam Carving 44

45 Wordle à Random The Wordle algorithm places one word at a (me in a greedy fashion, ie aiming to use space as efficiently as possible. First the words are sorted by weight/rank in decreasing order. Then for each word in the order, a posi(on is picked at random. 45

46 1: Random 46

47 2: Random 47

48 3: Random 48

49 4: Random 49

50 5: Random 50

51 6: Random 51

52 Context- Preserving Word Cloud Visualiza(on (CPWCV) First, a dissimilarity matrix is computed and Mul(dimensional Scaling (MDS) is performed Mul(dimensional Scaling (MDS) aims at detec(ng meaningful underlying dimensions in the data. Second, effort to create a compact layout 52

53 1: Context- Preserving 53

54 2: Context- Preserving : repulsive force 54

55 3: Context- Preserving : aprac(ve force 55

56 Seam Carving Basically, an algorithm for image resizing It was invented at Mitsubishi s 56

57 1: Seam Carving 57

58 2: Seam Carving : space is divided into regions 58

59 3: Seam Carving : empty paths trimmed out itera(vely 59

60 4: Seam Carving 60

61 5: Seam Carving 61

62 6: Seam Carving: space divided into regions 62

63 7: Seam Carving 63

64 3 New Algorithms 1. Inflate and Push 2. Star Forest 3. Cycle Cover 64

65 Inflate- and- Push Simple heuris(c method for word layout, which aims to preserve seman(c rela(ons between pair of words. Based on 1. Heuris(cs: scaling down all word rectangles by some constant; 2. Compu(ng MDS (mul(dimensional scaling) on the dissimilarity matrix 3. Iteretavely increase the size of rectangles by 5% (ie inflate words; 4. When words overlaps, apply a force- directed algorithm to push words away. 65

66 Inflate: star(ng point 66

67 Inflate : scaling down 67

68 Inflate : seman(cally- related words are placed close to each other. Apply inflate words (5%) itera(vely. 68

69 Inflate: push words : repulsive force to resolve overlaps 69

70 Inflate: final stage 70

71 Star Forest A star is a tree A star forest is a forest whose connected components are all stars. 71

72 Repe((on: trees and graphs A tree is special form of graph i.e. minimally connected graph and having only one path between any two ver(ces. In a graph there can be more than one path i.e. graph can have uni- direc(onal or bi- direc(onal paths (edges) between nodes. 72

73 Three steps 1. Extrac(ng the star forest: par&&on a graph into disjoint stars 2. Realising a star: build a word cloud for every star 3. Pack all the stars together 73

74 Star Forest : star = tree 1. Extract stars greedily from a dissimilarity matrix à disjoint stars = star forest 2. Compute the op(mal stars, ie the best set of words to be adjacent 3. Aprac(ve force to get a compact layout 74

75 Cycle Cover This algorithm is based on a similarity matrix. First, a similarity path is created Then, the op(mal level of compact- ness is computed 75

76 Quan(ta(ve Metrics 1. Realized Adjacenies how close are similar words to each other? 2. Distor(on how distant are dissimilar words? 3. Uniform Area U(liza(on uniformity of the distribu(on (overpopulated vs sparse areas in the word cloud) 4. Comptactness how well u(lized is the drawing area? 5. Aspect Ra(o width and height of the bounding box 6. Running Time execu(on (me 76

77 2 datasets (1) WIKI, a set of 112 plain- text ar(cles extracted from the English Wikipedia, each consis(ng of at least 200 dis(nct words (2) PAPERS, a set of 56 research papers published in conferences on experimental algorithms (SEA and ALENEX) in

78 Cycle Cover wins 78

79 Seam Carving wins 79

80 Random wins 80

81 Inflate wins 81

82 Random and Seam Carving win 82

83 All ok except Seam Carving 83

84 Demo 84

85 The end 85