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| 4 |
The structure of the book The introduction presents some basic background material,demarcates the subject and discusses loosely some of the problems in IR
...The two major chapters are those dealing with automatic classification and evaluation
...Outline Chapter 2:Automatic Text Analysis contains a straightforward discussion of how the text of a document is represented inside a computer
...Chapter 3:Automatic Classification looks at automatic classification methods in general and then takes a deeper look at the use of these methods in information retrieval
...Chapter 4:File Structures here we try and discuss file structures from the point of view of someone primarily interested in information retrieval
...Chapter 5:Search Strategies gives an account of some search strategies when applied to document collections structured in different ways
...Chapter 6:Probabilistic Retrieval describes a formal model for enhancing retrieval effectiveness by using sample information about the |
| 186 |
behaviour of any one of the components depends in only an aggregate way on the behaviour of the other components
...2
...On the file structure chosen and the way it is used depends the efficiency of an information retrieval system
...Inverted files have been rather popular in IR systems
...There are many more problems in this area which are of interest to IR systems
...3
...So far fairly simple search strategies have been tried
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| 134 |
which from a computational point of view would simplify things enormously
...An alternative way of using the dependence tree Association Hypothesis Some of the arguments advanced in the previous section can be construed as implying that the only dependence tree we have enough information to construct is the one on the entire document collection
...The basic idea underlying term clustering was explained in Chapter 2
...If an index term is good at discriminating relevant from non relevantdocuments then any closely associated index term is also likely to begood at this
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| 184 |
Eight THE FUTURE Future research In the preceding chapters I have tried to bring together some of the more elaborate tools that are used during the design of an experimental information retrieval system
...1
...Substantial evidence that large document collections can be handled successfully by means of automatic classification will encourage new work into ways of structuring such collections
...It is therefore of some importance that using the kind of data already in existence,that is using document descriptions in terms of keywords,we establish that document clustering on large document collections can be both effective and efficient
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| 133 |
3
...It must be emphasised that in the non linear case the estimation of the parameters for g x will ideally involve a different MST for each of P x w 1 and P x w 2
...There is a choice of how one would implement the model for g x depending on whether one is interested in setting the cut off a prior or a posteriori
...If one assumes that the cut off is set a posteriori then we can rank the documents according to P w 1 x and leave the user to decide when he has seen enough
...to calculate estimate the probability of relevance for each document x
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| 9 |
Sparck Jones has carried on this work using measures of association between keywords based on their frequency of co occurrence that is,the frequency with which any two keywords occur together in the same document
...The term information structure for want of better words covers specifically a logical organisation of information,such as document representatives,for the purpose of information retrieval
...The organisation of these files is produced by an automatic classification method
...Evaluation of retrieval systems has proved extremely difficult
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| 5 |
frequency of occurrence and co occurrence of index terms in the relevant and non relevant documents
...Chapter 7:Evaluation here I give a traditional view of the measurement of effectiveness followed by an explanation of some of the more promising attempts at improving the art
...Chapter 8:The Future contains some speculation about the future of IR and tries to pinpoint some areas of research where further work is desperately needed
...Information retrieval Since the 1940 s the problem of information storage and retrieval has attracted increasing attention
...In principle,information storage and retrieval is simple
...When high speed computers became available for non numerical work,many thought that a computer would be able to read an entire document collection to extract the relevant documents
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| 109 |
retrieval
...Anew classic paper on the limitations of a Boolean search is Verhoeff et al
...References 1
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| 32 |
If we think of a simple retrieval strategy as operating by matching on the descriptors,whether they be keyword names or class names,then expanding representatives in either of these ways will have the effect of increasing the number of matches between document and query,and hence tends to improve recall
...Recall is defined in the introduction
...Jones [41]has reported a large number of experiments using automatic keyword classifications and found that in general one obtained a better retrieval performance with the aid of automatic keyword classification than with the unclassified keywords alone
...Unfortunately,even here the evidence has not been conclusive
...The discussion of keyword classifications has by necessity been rather sketchy
...Normalisation It is probably useful at this stage to recapitulate and show how a number of levels of normalisation of text is involved in generating document representatives
...Index term weighting can also be thought of as a process of normalisation,if the weighting scheme takes into account the number of different index terms per document
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