Analysis of Multiterm Queries in Partitioned Signature File Environments

The concern of this study is the signature files which are used for information storage and retrieval in both formatted and unformatted databases. The analysis combines the concerns of signature extraction and signature file organization which have usually been treated as separate issues. Both the uniform frequency and single term query assumptions are relaxed and a comprehensive analysis is presented for multiterm query environments where terms can be classified based on their query and database occurrence frequencies. The performance of three superimposed signature generation schemes is explored as they are applied to a dynamic signature file organization based on linear hashing: Linear Hashing with Superimposed Signatures (LHSS). First scheme (SM) allows all terms set the same number of bits regardless of their discriminatory power whereas the second and third methods (MMS and MMM) emphasize the terms with high query and low database ooccurrence frequencies. Of these three schemes, only MMM takes the probability distribution of the number of query terms into account in finding the optimal mapping strategy. The main contribution of the study is the derivation of the performance evaluation formulas which is provided together with the analysis of various experimental settings. Results indicate that MMM outperforms the other methods as the gap between the discriminatory power of the terms gets larger. The absolute value of the savings provided by MMM reaches a maximum for the high query weight case. However, the extra savings decline sharply for high weight and moderately for the low weight queries with the increase in database size. The applicability of the derivations to other partitioned signature organizations is discussed and a detailed analysis of Fixed Prefix Partitioning (FPP) is provided as an example. An approximate formula that is shown to estimate the performance of both FPP and LHSS within an acceptable margin of error is also modified to account for the multiterm case

Signature Files: An Integrated Access Method for Formatted and Unformatted Databases

The signature file approach is one of the most powerful information storage and retrieval techniques which is used for finding the data objects that are relevant to the user queries. The main idea of all signature based schemes is to reflect the essence of the data items into bit pattern (descriptors or signatures) and store them in a separate file which acts as a filter to eliminate the non aualifvine data items for an information reauest. It provides an integrated access method for both formattid and formatted databases. A complative overview and discussion of the proposed signatnre generation methods and the major signature file organization schemes are presented. Applications of the signature techniques to formatted and unformatted databases, single and multiterm query cases, serial and paratlei architecture. static and dynamic environments are provided with a special emphasis on the multimedia databases where the pioneering prototype systems using signatnres yield highly encouraging results

Analysis of Signature Generation Schemes for Multiterm Queries In Partitioned Signature File Environments

Our analysis explores the performance of three superimposed signature generation schemes as they are applied to a dynamic sigrtature file organization based on linear hashing: Linear Hashing with Superinzposed Signatures (LHSS). First scheme (SM) allows all terms set the same number of bits whereas the second and third methods (MMS and MMM) emphasize the terms with hlgh discriminatory power. In addition, M Mco nsiders the probaOiZity distribution of the number of query terms. The main contribution of the study is the combination of signature generation and signature file organization concepts together with the relaxation of the single term query and uniform frequency assumptions. The derivation of the performance evaluation formulas are provided as well as the analysis of various experimental settings. Results indicate that MMM outperforms the others as terms become more distinctive in their discriminatory power. MMM accomplishes the highest savings in retrieval eficiency for the high query weight case. We also discuss the applicability of the derivations to other partitioned signature organizations providing a detailed analysis of Fixed Prefix Partitioning (FPP) as an example. Finally, an appro.ximate perfortnance evaluation formula that works for both FPP and LHSS is modijied to account for the multiterm case

Dynamic Signature File Partitioning Based on Term Characteristics

Signature files act as a filter on retrieval to discard a large number of non-qualifying data items. Linear hashing with superimposed signatures (LHSS) provides an effective retrieval filter to process queries in dynamic databases. This study is an analysis of the effects of reflecting the term query and occurrence characteristics to signatures in LHSS. This approach relaxes the unrealistic uniform frequency assumption and lets the terms with high discriminatory power set more bits in signatures. The simulation experiments based on the derived formulas show that incorporating the term characteristics in LHSS improves retrieval efficiency. The paper also discusses the further benefits of this approach to alleviate the potential imbalance between the levels of efficiency and relevancy

Signature File Hashing Using Term Occurrence and Query Frequencies

Signature files act as a filter on retrieval to discard a large number of non-qualifying data items. Linear hashing with superimposed signatures (LHSS) provides an effective retrieval filter to process queries in dynamic databases. This study is an analysis of the effects of reflecting the term occurrence and query frequencies to signatures in LHSS. This approach relaxes the unrealistic uniform frequency assumption and lets the terms with high discriminatory power set more bits in signatures. The simulation experiments based on the derived formulas explore the amount of page savings with different occurrence and query frequency combinations at different hashing levels. The results show that the performance of LHSS improves with the hashing level and the larger is the difference between the term discriminatory power values of the terms, the higher is the retrieval efficiency. The paper also discusses the benefits of this approach to alleviate the imbalance between the levels of efficiency and relevancy in unrealistic uniform frequency assumption case

Effect of Hepatosteatosis on the Virological Response in Entecavir and Tenofovir Therapies

Objective: Both chronic hepatitis B (CHB) and hepatosteatosis may lead to necroinflammation in liver. Therefore, the presence of hepatosteatosis might negatively affect the efficacy of antiviral therapy. We aimed to determine the effect of hepatosteatosis on virological response in patients with CHB receiving entecavir (ETV) and tenofovir (TDF) treatment

Awareness Of Hepatitis B Virus Reactivation Among Physicians Administering Immunosuppressive Treatment And Related Clinical Practices

Objective: This study aimed to evaluate the awareness and knowledge levels of all physicians administering immunosuppressive treatment concerning hepatitis B virus (HBV) reactivation, and draw attention to the importance of the subject through evaluation. Methods: The study was carried out by infectious diseases and clinical microbiology specialists in 37 health centers, and it was performed in Turkey between January and March 2017. All specialists providing a written consent and working in the departments of Medical Oncology, Hematology, Dermatology and Venereology, Physical Medicine and Rehabilitation, and Rheumatology of each study center were included in the study. Results: A total of 430 physicians participated in the study. Their mean age was 39.87 +/- 7.42 years, and 47.9% of them were males. During their career, 39.3% of these physicians had encountered patients developing HBV reactivation while receiving immunosuppressive treatment. The rate of encountering patients who died due to HBV reactivation was 6.5%. 97% of physicians who participated, considered the risk of HBV reactivation to be important. 70.2% of physicians stated that guidelines related to HBV reactivation and antiviral treatment for these patients were discussed in the congresses they participated, regarding their specialties. The rate of performing hepatitis screening among physicians whose patients developed HBV reactivation was statistically significantly higher than those physicians who had no patients with HBV reactivation (p<0.05). Physicians who used the guidelines related to HBV reactivation in their specialties performed screening for the HBV infection much more often than physicians who did not use the guidelines (p=0.002). Conclusions: According to the results obtained in our study, the rates of conducting screening and awareness of HBV reactivation among physicians administering immunosuppressive treatment were higher compared with similar studies; however, their awareness that HBV DNA and anti-HBc should be utilized much more frequently among the serological tests they use for screening of HBV infection, should be increased.WoSScopu