Structured Environment - Computer and Information Science - Lecture Slides, Slides of Applications of Computer Sciences

Download Structured Environment - Computer and Information Science - Lecture Slides and more Slides Applications of Computer Sciences in PDF only on Docsity!

Dynamic Element Retrieval IN A

Structured Environment

CONTENTS

Introduction

Retrieval Environment

• The Vector Space Model
• INEX Environment
• Flexible Retrieval System

Method Used for Retrieval

• Document Tree – Construction
• Ranking of Elements
• Output

Experiments

Conclusions

RETRIEVAL ENVIRONMENT

• 2 Factors – Issues when focus moves from documents to components and Salton’s Vector Space Model
• Vector Space Model – Weight number of times a term occurs in the document
• Fox’s Extended Vector Space Model – Incorporation of objective identifiers
• Document vector consists of subvectors
• Contain text independently indexed, weighted, searched and retrieved
• Term Weighting – weighting within subjective vectors
• Smart Experimental Retrieval System

INEX ENVIRONMENT

• Content Only (CO) – ignore document structure, like typical queries, specify only content of search
• Content and Structure (CAS) – explicitly refer to structure, exhaustive and specific
• CO query directly to user, CAS additional filtering and search of body portion
• CAS returns rank ordered list of elements
• INEX-EVAL – uses measures of recall and precision

( fig, exhaustivity, specificity mapped to a single relevance) results are ranked

METHOD FOR FLEXIBLE RETRIEVAL

• Input – Query Q given and paragraph, retrieve rank ordered list, terminal modes
• N top ranked paragraphs as input selected
• Set of paragraphs used to identify documents – elements generated and returned as output
• Document Tree – Needs information of structure

Terminal nodes Pre-order traversal Terminal nodes found in paragraph index

CONSTRUCTION OF DOCUMENT TREE

• For query Q, n top ranked paras used to build trees
• Leaf elements or terminal nodes - paragraph nodes
• Each leaf represented by term-freq weighted frequency vector
• 1 st^ – gather all leaf nodes, terminal nodes done
• 2 nd^ – merge children vectors for parents
• Document schema determine merging
• Parent – unique terms of children, term – freq weighted parent vector( has content of children)
• Process in recursive manner done

• Ltu weighting – N collection size, nk no of elements

((1+log(term_freq))/log(N/nk))/ ((1-slope)+slope*(no_unique_terms)/pivot))

• N,nk element dependent, should be known through indexing
• We move up; N – count elements of each type
• Nk – inverted file entry in paragraph index, mapping identifiers and xpaths (given)

OUTPUT OF FLEXIBLE RETRIEVAL

• Select another leaf node, gather siblings, construct document tree, calculate Lnu term weights, Ltu weighted query; produce another rank ordered list
• After n top ranked exhausted, last list produced, merge lists
• Single set of elements rank ordered – correlation Q
• Comparison – flexible retrieval & all-element index

identical – set of n paragraphs i/p to flexible retrieval have all paragraphs same values used for Lnu-ltu

FACTORS OF INTEREST

• Slope, pivot for Lnu-ltu
• Effective structure retrieval
• Can be determined – empirically, applied from one collection to other; Generic
• N- no of paragraphs input, sets upper bound on number per query
• Actual trees depend on number of paragraphs having same group or same document

EXPERIMENTS DONE

• All-element and dynamic/flexible retrieval experiments and results
  • body-only retrieval
• Correlation between element and query vector produced – correlation of body elements only

Table 1

DISCUSSIONS AND CONCLUSIONS

• Flexible retrieval dynamically, rank ordered list of elements, single indexing at level - basic indexing node (paragraph)
• Basic functions- SMART; extended vector model
• Results – flexible capabilities
• Attempt to incorporate other subvectors, internal node, weight
• INEX – exhaustivity and specificity; results exhaustive; specificity research going on; results are reflection
• It is the better way of retrieval than all-indexing