Dimitrios Dervos

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The current study considers the superimposed coding variation of the signature file method (SC-SF). A number of issues which are not clearly specified in the literature are addressed by adopting a unified approach which makes possible the comparison of two SC-SF models. Heuristic analytic derivations of earlier studies are shown to be valid by analysis and(More)
Today, two classes of indexing methods enjoying wide applicability are the Inverted Index and the Superimposed Coding based Signature File (SC-SF). The former is most efficient in query processing but utilizes extra storage of size comparable to that of the textbase, whereas the latter is most efficient in storage utilization. The present study builds upon(More)
The f-value is a new indicator that measures the importance of a research article by taking into account all citations received, directly and indirectly, up to depth n. The f-value considers all information present in a Citation Graph in order to produce a ranking of the articles. Apart from the mathematical equation that calculates the f-value, we also(More)
A new methodology is introduced, where blocks of text are replaced by a compressed, fully reversible, signature pattern. Full reversibility implies zero information loss, thus the new method is termed Perfect Encoding. The method’s analytical model is produced and, where applicable, contrasted with the current practice in signature file organizations.(More)
In this presentation the audience will be: (a) introduced to the aims and objectives of the DBTechNet initiative, (b) briefed on the DBTech EXT virtual laboratory workshops (VLW), i.e. the educational and training (E&T) content which is freely available over the internet and includes vendor-neutral hands-on laboratory training sessions on key database(More)
A new method for ranking the output of the superimposed variation of the signature file method (SC/SF) is presented. The method is termed 'Binary Ranking' and assigns a value ('B-rank value') to each block candidacy of the signature file output in a way which reflects the credibility of the signature to stand in place of the corresponding real text. In(More)
DBTechNet is a network of teachers, trainers and professionals from HE institutions, VET institutions, and ICT companies. To synchronize the coverage of basic database topics in VET and HE curricula, DBTechNet has conducted a survey in a number of European VET institutions. The survey has revealed the absence of SQL transactions in many of today's VET(More)
Here we report on our implementation of a hybrid-indexing scheme (bitmap-tree) that combines the advantages of bitmap indexing and file inversion. The results we obtained are compared to those of the compressed inverted file index. Both storage overhead and query processing efficiency are taken into consideration. The proposed new method is shown to excel(More)