A new interpretation for null values in the weak instance model

AbstractA new definition of the weak instance model for relational databases is presented, which does not consider the missing values as existent though unknown, but just assumes that no information is available about them. It is possible to associate with the new definition logical theories that do not contain existentially quantified variables. The new model enjoys various desirable properties of the classic weak instance model, with respect to dependency satisfaction, query answering, and associated logical theories

Canonical queries as a query answering device (Information Science)

Issued as Annual reports [nos. 1-2], and Final report, Project no. G-36-60

Trust, Commitment, Fidelity, and Condom Use among Young Adults in Tanzania

With an estimated 7 percent of Tanzanian adults HIV positive and no cure or vaccine available, preventing HIV infection remains central to fighting the AIDS epidemic. For sexually active individuals there are two ways to avoid HIV infection: fidelity with an uninfected partner or consistent condom use. Trust and commitment play a complex but critical role in both fidelity and condom use. Research on the link between trust and condom use is emerging, yet the relationship between trust, commitment, and fidelity has yet to be explored. Of the three standard methods of AIDS prevention--abstinence, fidelity, and condom use--fidelity remains relatively under-researched. This dissertation aims to improve our understanding of trust and commitment in Tanzania and the relationship that trust and commitment have with fidelity and condom use using multiple theories and multiple methods (semi-structured in-depth interviews and in-person survey interviews). Analysis of in-depth interviews with young residents of Mtoni, Dar es Salaam suggests that the youth place an important value on satisfaction with their relationship, feeling that their partners understand them, being able to rely on their partners for instrumental and emotional support, and their partner's sexual fidelity. The youth in Mtoni often found it difficult to differentiate trust from commitment and trust from fidelity. Path analysis suggests that equity theory and investment theory do not accurately describe the development of commitment among Tanzanian youth. Identity theory, however, may accurately explain the development of trust and commitment among Tanzanian youth. We found associations in our data that are consistent with the identity theory model. Analysis of the in-depth interviews suggested that sexual fidelity, trust, and commitment are important to stable relationships yet that once sexual fidelity, trust, and commitment are established, the couple is unlikely to use condoms. However, the associations expected between these variables were not clearly evident in the quantitative data. A generalized trust in one's partner was not found to be associated with a lower level of condom use. Similarly, we did not find that a general trust in a partner or a general feeling of commitment was related to fidelity