Valid Time and Transaction Time Proposals: Language Design Aspects

Several proposals (such as [5], [6]) have been presented to ISO for consideration as temporal extensions to SQL. These proposals are based on approaches to valid time and transaction time, wherein the regular syntax for invocation of SQL operators on tables is interpreted in a special manner, based on the existence of "hidden" timestamps. Concerns about such an approach, with reference to these specific proposals, have been expressed ([8]). Those concerns have been responded to ([4]). We further clarify our concerns and align them with stated language design principles that we believe to be generally agreed upon. We respond to [4] in the context of these principles. Although this discussion is taking place in the specific context of proposals for international standardization, we believe its import is of wider concern than that, meriting the attention of the temporal database community in general. Furthermore, [5] and [6] appear to be the most precise specifications to date to be based on the approach in question; for that reason, we invite people who are not interested in standardization to examine the wider issues that might be emerging from discussions based on those proposals.